Pregnancy, Childbirth & Puerperium

Gestational diabetes: screening, diagnosis, management

Clinical Overview and When to Suspect Gestational Diabetes

— Maternal: preeclampsia, polyhydramnios, cesarean delivery, future T2DM (~50% lifetime risk).

— Fetal/neonatal: macrosomia, shoulder dystocia, birth trauma, neonatal hypoglycemia, hyperbilirubinemia, RDS, stillbirth.

— Long-term offspring: childhood obesity, metabolic syndrome.

— BMI ≥25 (≥23 in Asian Americans) plus ≥1 risk factor

— Prior GDM, prior macrosomic infant (≥4000–4500 g), prior unexplained stillbirth

— First-degree relative with diabetes

— PCOS, hypertension, dyslipidemia, cardiovascular disease

— A1c ≥5.7%, prior IGT/IFG, or acanthosis nigricans

— High-risk ethnicity

Board pearl: A woman with risk factors who screens negative early in pregnancy still needs the routine 24–28 week screen — early-negative does not exempt her. Conversely, a positive early screen meeting overt-DM criteria is managed as pregestational diabetes, not GDM.

Definition: Gestational diabetes mellitus (GDM) = glucose intolerance with onset or first recognition during pregnancy, typically diagnosed in the second or third trimester, that is not clearly overt (pregestational) diabetes.

Epidemiology: Affects ~6–9% of US pregnancies; rising with obesity epidemic and advanced maternal age. Higher prevalence in Hispanic, South/East Asian, Native American, and Black populations.

Pathophysiology: Placental hormones (human placental lactogen, progesterone, cortisol, GH) drive insulin resistance peaking at 24–28 weeks. GDM emerges when maternal β-cell reserve cannot compensate.

Why it matters on Step 3:

When to suspect early (first prenatal visit): Screen for undiagnosed overt diabetes at intake if any high-risk feature:

Universal screening: All pregnant women between 24–28 weeks regardless of risk factors (ACOG, ADA, USPSTF Grade B).

Clinical clues mid-pregnancy: Fundal height greater than dates, glycosuria on routine dip (insensitive but suggestive), polyhydramnios on US, accelerated fetal growth.

Presentation Patterns and Key History

— 28-year-old G2P1 at 26 weeks with BMI 31, prior 4.2 kg infant → due for 1-hour GCT.

— 32-year-old at 12 weeks with PCOS, A1c 6.0% → early screening required.

— 30-year-old at 30 weeks with fundal height 4 cm > dates and polyhydramnios on US → screen even if earlier test was normal.

— Recurrent monilial vaginitis or UTIs in pregnancy → consider undiagnosed hyperglycemia.

— Obstetric history: prior GDM (recurrence ~50%), prior macrosomia, shoulder dystocia, unexplained stillbirth, congenital anomalies (suggests pregestational), preeclampsia.

— Family history: first-degree relative with T2DM.

— Personal medical: PCOS, chronic HTN, dyslipidemia, prior steroid exposure, atypical antipsychotics, HIV protease inhibitors.

— Lifestyle/social: diet quality, physical activity, weight gain pattern, food insecurity (affects management plan), language and literacy for nutrition counseling.

— Current pregnancy: gestational weight gain (excessive early gain is a risk factor), prior 1st-trimester A1c, prior abnormal random glucose.

— Fasting plasma glucose ≥126, random ≥200 with symptoms, or A1c ≥6.5% at <20 weeks → overt (pregestational) DM, not GDM.

— These patients need anomaly screening (fetal echo, detailed anatomy at 18–22 weeks) because hyperglycemia at organogenesis raises congenital heart disease and neural tube defect risk.

Key distinction: GDM does NOT cause congenital anomalies because hyperglycemia onset is after organogenesis; pregestational diabetes does. If a stem features anomalies, the underlying diagnosis is pregestational DM mislabeled as GDM.

Asymptomatic is the rule. GDM is overwhelmingly detected by routine screening, not symptoms. A stem describing classic polyuria/polydipsia/weight loss in pregnancy should push you toward overt/pregestational diabetes rather than typical GDM.

Typical Step 3 vignette patterns:

Key history to elicit:

Distinguish from overt diabetes in pregnancy using initial labs:

Physical Exam Findings (and Obstetric Assessment)

— Acanthosis nigricans (posterior neck, axillae) — insulin resistance marker.

— Skin tags, central obesity, elevated BMI.

— Hirsutism, male-pattern alopecia → suggests PCOS background.

— Elevated blood pressure → screen for chronic HTN and superimposed preeclampsia.

— Fundal height > dates by ≥3 cm → suspect macrosomia, polyhydramnios, or multiple gestation; order ultrasound.

— Tense, globular uterus with difficult fetal palpation → polyhydramnios.

— Estimated fetal weight ≥90th percentile or asymmetric growth (abdominal circumference > head) on US — classic GDM growth pattern reflecting fetal hyperinsulinemia driving truncal adiposity.

— Decreased fundal height or oligohydramnios in the setting of vasculopathy → think pregestational DM rather than GDM.

— BP ≥140/90 with headache, RUQ pain, visual changes → preeclampsia evaluation.

— Decreased fetal movement → NST.

— Polyuria/polydipsia, nausea, abdominal pain, Kussmaul breathing → check for DKA, which can occur at lower glucose levels in pregnancy (euglycemic DKA at glucose <200).

Step 3 management: A GDM patient at 32 weeks with fundal height 36 cm → order growth ultrasound and amniotic fluid index, not just reassurance. Macrosomia and polyhydramnios change delivery planning.

Maternal exam is usually unremarkable. Findings, when present, reflect either risk factors or downstream complications.

Risk-factor signs:

Obstetric exam clues to hyperglycemia or its complications:

Blood pressure and edema: Document at every visit; GDM raises preeclampsia risk ~2-fold. Reassess for proteinuria if BP rises.

Funduscopic and foot exam: Generally not part of routine GDM care, but if patient is reclassified as having overt diabetes early in pregnancy, perform dilated eye exam in 1st trimester and foot exam because retinopathy can progress rapidly with rapid glycemic correction in pregnancy.

Hemodynamic red flags requiring urgent workup:

Diagnostic Workup — Screening and Diagnostic Glucose Testing

— Step 1: 1-hour 50 g GCT (non-fasting) at 24–28 weeks.

— Threshold: ≥130, 135, or 140 mg/dL (institution-dependent; 140 is most common).

— If <threshold → screen complete.

— If ≥threshold → proceed to step 2.

— A 1-hour value ≥200 mg/dL is often treated as diagnostic of GDM without 3-hour testing.

— Step 2: 3-hour 100 g OGTT (fasting).

— Carpenter–Coustan criteria (mg/dL): fasting ≥95, 1 hr ≥180, 2 hr ≥155, 3 hr ≥140.

— Diagnosis: ≥2 abnormal values = GDM. One abnormal value → repeat in 4 weeks or treat as impaired (varies by institution; some treat as GDM).

— 75 g 2-hour OGTT at 24–28 weeks, fasting.

— Thresholds (mg/dL): fasting ≥92, 1 hr ≥180, 2 hr ≥153.

— Any single abnormal value = GDM.

— Fasting ≥126, random ≥200 with symptoms, A1c ≥6.5%, or 2-hr 75 g OGTT ≥200 → overt DM.

— Sub-diabetic-range hyperglycemia early may be labeled "early GDM" and treated similarly.

— A1c (informative but not diagnostic for GDM mid-pregnancy due to red cell turnover changes; lower normal range in pregnancy).

— Baseline urine protein/creatinine, TSH if symptomatic, LFTs/BMP if hypertensive.

— Eye exam only if reclassified as overt DM.

Board pearl: The 1-hour GCT does not require fasting. If a stem says the patient "skipped breakfast" before the 50 g test, that's irrelevant — but for the 3-hour 100 g and the 2-hour 75 g, fasting overnight is mandatory or the test is invalid.

Two acceptable US strategies (know both for Step 3):

Two-step approach (most common in US, ACOG-preferred):

One-step approach (ADA-acceptable, IADPSG):

Early screening (<20 weeks) for high-risk women uses standard nonpregnant criteria:

Adjunct labs at diagnosis:

Diagnostic Workup — Fetal Surveillance and Confirmatory Studies

— Self-monitored blood glucose (SMBG) 4×/day: fasting + 1- or 2-hour postprandial after each meal.

— Targets:

— Fasting <95 mg/dL

— 1-hour postprandial <140 mg/dL

— 2-hour postprandial <120 mg/dL

— Urine ketones if poor weight gain, illness, or caloric restriction (starvation ketosis worsens fetal outcomes).

— A1c every trimester if on pharmacotherapy; target <6.0–6.5% if achievable without hypoglycemia.

— Detailed anatomy scan at 18–22 weeks, with fetal echocardiogram added only for women with pregestational diabetes (or early-diagnosed GDM with A1c ≥6.5%), not standard GDM.

— Growth ultrasound at 32–36 weeks to estimate fetal weight and screen for macrosomia/polyhydramnios.

— GDMA1 (diet-controlled, well-controlled): No mandatory antenatal testing in many protocols; some begin twice-weekly NSTs at 36 weeks. Local guidelines vary.

— GDMA2 (medication-requiring) or poorly controlled: Twice-weekly NST ± AFI starting at 32 weeks, earlier if comorbidities (HTN, prior stillbirth).

— Daily fetal kick counts from ~28 weeks for all.

— Review SMBG log every 1–2 weeks.

— If ≥30–50% of values above target over 1–2 weeks despite diet/exercise → escalate to pharmacotherapy.

— Estimate fetal weight near term.

— If EFW ≥4500 g in GDM (≥4000 g in pregestational DM) → discuss scheduled cesarean to reduce shoulder dystocia risk.

CCS pearl: When you diagnose GDM on CCS, order in this cluster: glucometer + test strips, nutrition consult (medical nutrition therapy), diabetes education, A1c, growth US around 32 weeks, NST schedule if GDMA2, then advance the clock 1–2 weeks to recheck logs.

After GDM diagnosis, baseline workup:

Fetal anatomic and growth surveillance:

Antepartum testing (NST/BPP):

Reassessment for treatment escalation:

Delivery planning evaluation:

Risk Stratification and First-Line Management Logic

— GDMA1: controlled with medical nutrition therapy (MNT) and exercise alone.

— GDMA2: requires pharmacologic therapy to meet glucose targets.

— Referral to registered dietitian within 1 week of diagnosis.

— Caloric target individualized; typical ~30 kcal/kg/day for normal BMI, reduced for obesity (~25 kcal/kg) — never <1600–1800 kcal/day to avoid ketosis.

— Macronutrient distribution: ~40% complex carbs, 20% protein, 40% fat, with carbs spread across 3 meals + 2–3 snacks (bedtime snack to prevent overnight fasting hypoglycemia/ketosis).

— Limit simple sugars; emphasize low-glycemic-index foods, fiber.

— 30 minutes moderate activity most days (walking after meals especially effective at blunting postprandial peaks).

— Contraindications: placenta previa with bleeding, preterm labor, severe preeclampsia, ruptured membranes.

— Continue MNT alone if majority of values at target.

— Initiate pharmacotherapy if:

— Fasting ≥95 mg/dL persistently, OR

— 1-hour postprandial ≥140 / 2-hour ≥120 persistently, OR

— Macrosomia/polyhydramnios on US despite "in-target" SMBG (consider unrecognized hyperglycemia).

— Underweight: 28–40 lb

— Normal: 25–35 lb

— Overweight: 15–25 lb

— Obese: 11–20 lb

Step 3 management: A GDM patient at 30 weeks with fasting glucose 88 but 1-hour postprandial 165 most days despite MNT for 2 weeks → start insulin (do not just "intensify diet again"). Persistent postprandial elevations are an indication to escalate.

Classification drives management intensity:

Step 1 — Medical nutrition therapy (first-line for ALL GDM):

Step 2 — Exercise:

Step 3 — SMBG and 1–2 week reassessment:

Weight gain targets (IOM, by prepregnancy BMI):

Pharmacotherapy — Insulin as First-Line, Oral Agents as Alternatives

— Failure to meet glucose targets after 1–2 weeks of MNT.

— Severe initial hyperglycemia (fasting ≥110, random ≥200, A1c ≥6.5%) — start at diagnosis.

— Elevated fasting only: bedtime NPH or detemir (long-acting basal). Start ~0.1–0.2 U/kg.

— Elevated postprandial only: rapid-acting (lispro or aspart) before that meal. Start ~2 U and titrate.

— Mixed pattern: basal-bolus regimen — typical starting total daily dose 0.7–1.0 U/kg/day (rising across trimesters: 0.7 in 1st, 0.8 in 2nd, 0.9–1.0 in 3rd), split ~50% basal / 50% bolus divided across meals.

— Adjust every 3–7 days by 10–20% based on patterns.

— Aspart, lispro (rapid) — well-studied.

— NPH, detemir (basal) — extensive safety data.

— Glargine — acceptable; less pregnancy-specific data but commonly used.

— Avoid regular insulin SC as first-line bolus due to slower onset and higher hypoglycemia risk.

— Metformin: crosses placenta; useful when insulin refused or unaffordable. ~25–40% will still need insulin added. Long-term offspring effects under study.

— Glyburide: crosses placenta more than once thought; higher rates of neonatal hypoglycemia and macrosomia vs insulin — not first-line.

— Counsel patient on insulin's preferred status; document shared decision-making if oral chosen.

Board pearl: A stem giving you GDM with isolated fasting hyperglycemia despite diet → answer is bedtime NPH (or detemir), not prandial insulin and not metformin. Match the regimen to the abnormal time point.

Insulin is the gold-standard pharmacotherapy in pregnancy (ACOG, ADA): does not cross the placenta, most predictable, titratable.

When to start insulin:

Regimen selection based on pattern:

Preferred insulins in pregnancy:

Oral agents (second-line, ACOG-acknowledged but no longer preferred):

Hypoglycemia management: 15 g fast carbs, recheck in 15 min; patient and family trained on glucagon if on insulin.

Intrapartum Management and Delivery Timing

— GDMA1, well-controlled: expectant management; deliver by 40 0/7–40 6/7 weeks (do not exceed 41 weeks).

— GDMA2, well-controlled on meds: deliver 39 0/7–39 6/7 weeks.

— Poorly controlled GDM: individualize 37 0/7–38 6/7 weeks; earlier (34–36 wks) only with additional indications (preeclampsia, abnormal testing) — give antenatal corticosteroids if <37 wks and monitor glucose closely.

— Offer scheduled cesarean if EFW ≥4500 g in GDM (≥4000 g in pregestational DM) to reduce shoulder dystocia/brachial plexus injury.

— Otherwise, vaginal delivery is appropriate; counsel on shoulder dystocia signs.

— Target maternal glucose 70–110 mg/dL (some institutions 70–125) to minimize neonatal hypoglycemia.

— GDMA1: check glucose every 4–6 h in labor; usually no insulin needed.

— GDMA2 / pregestational DM: check every 1–2 h; use insulin drip + D5 infusion protocol if glucose >110–120.

— Hold long-acting insulin on morning of induction/elective cesarean; manage with sliding scale or drip.

— Causes hyperglycemia for 5–7 days — increase insulin ~25% during this window and check glucose q2–4h; consider IV insulin if severe.

— Discontinue all GDM insulin/orals immediately after delivery of placenta — insulin resistance falls precipitously.

— Resume only if glucose remains elevated (>180) — suggests undiagnosed type 2.

— Check fasting glucose during postpartum hospitalization.

— Check neonatal glucose at 30 min, then q1h × several hours; treat hypoglycemia per nursery protocol.

— Early feeding (breast or formula) within first hour.

— Monitor for polycythemia, hyperbilirubinemia, hypocalcemia, RDS.

CCS pearl: On CCS for a GDMA2 patient in labor: order fingerstick glucose q1h, IV access, fetal monitoring, hold subQ insulin, start D5LR + insulin drip if glucose >110, anesthesia consult, neonatology to be present at delivery.

Delivery timing (ACOG):

Mode of delivery:

Intrapartum glucose management:

Steroids for fetal lung maturity (<37 wks):

Postpartum immediate care:

Neonatal care:

Special Populations — Renal/Hepatic Impairment and Comorbidity

— Pregestational DM with nephropathy carries higher GDM-mimicking patterns; differentiate by early A1c and pre-pregnancy records.

— Avoid metformin if eGFR <30; caution between 30–45 (rarely an issue in young pregnant patients but relevant in older gravidas or with diabetic nephropathy).

— Adjust insulin downward as pregnancy advances if eGFR declines — renal clearance of insulin falls, risking hypoglycemia.

— Monitor urine protein/Cr ratio at each visit; nephropathy raises preeclampsia and IUGR risk.

— Low-dose aspirin 81 mg starting at 12–16 weeks for preeclampsia prophylaxis in CKD or prior preeclampsia.

— Rare in reproductive-age women but consider in patients with NAFLD, prior cholestasis.

— Acute fatty liver of pregnancy and HELLP can mimic worsening GDM with hypoglycemia — check LFTs, platelets, LDH if new RUQ pain or unexplained hypoglycemia in 3rd trimester.

— Metformin generally safe with mild hepatic dysfunction; avoid with active liver disease.

— Higher GDM prevalence and higher rates of chronic HTN, preeclampsia, cesarean.

— Counsel about combined risks; intensify surveillance.

— Post–bariatric surgery patients: GCT/OGTT can cause dumping syndrome; use alternative — fasting glucose + 1- and 2-hour postprandial SMBG for 1 week at 24–28 weeks, or A1c + fructosamine. Document the deviation.

— Higher insulin doses (often >1 U/kg/day late pregnancy).

— Higher GDM risk; same screening timing.

— Caloric needs higher; delivery typically earlier (37–38 wks dichorionic).

— Anticipate hyperglycemia; preemptive insulin adjustment.

Key distinction: New-onset hypoglycemia in a previously well-controlled insulin-requiring patient in late pregnancy is a red flag — consider placental insufficiency, preeclampsia/HELLP, or fetal demise. Do not just reduce insulin; evaluate fetus and maternal labs first.

Chronic kidney disease in pregnancy:

Hepatic impairment:

Advanced maternal age (≥35):

Obesity (BMI ≥30) and bariatric surgery history:

Multiple gestation:

Steroid or antipsychotic exposure:

Special Populations — Adolescent, Cultural, and Postpartum Reclassification

— GDM less common but emerging with adolescent obesity; manage identically.

— Address nutrition literacy, school logistics for SMBG, parental involvement, and confidentiality under state minor-consent laws.

— Long-acting reversible contraception (LARC) counseling at postpartum visit is high-yield.

— Effective MNT requires culturally-appropriate dietitian referral — South Asian, Hispanic, and other carb-dense cuisines need substitution strategies, not blanket restriction.

— Address food insecurity (refer to WIC, SNAP); restrictive diet plans fail if patient cannot afford alternatives.

— Religious fasting (e.g., Ramadan): generally discourage fasting in GDM; if patient insists, intensify glucose monitoring and individualize plan with endocrinology.

— 75 g 2-hour OGTT at 4–12 weeks postpartum for ALL women with GDM.

— Interpretation (nonpregnant criteria):

— Normal: fasting <100 and 2-hr <140.

— Prediabetes: fasting 100–125 (IFG) or 2-hr 140–199 (IGT).

— Diabetes: fasting ≥126 or 2-hr ≥200 (confirm).

— Alternative: fasting plasma glucose or A1c if OGTT not feasible (slightly less sensitive).

— Lifelong screening for T2DM every 1–3 years (every year if prediabetes).

— ~50% develop T2DM within 10 years.

— Preconception A1c <6.5% before next pregnancy.

— Recurrence risk of GDM ~30–50%.

Board pearl: A GDM patient at her 6-week postpartum visit who feels "back to normal" — the correct order is 75 g 2-hr OGTT, not "no further testing" and not "A1c only." This is one of the most commonly missed Step 3 GDM items.

Adolescent pregnancy:

Cultural and dietary tailoring:

Patients with limited English proficiency: Use professional interpreters, not family members, for nutrition and insulin teaching — directly tested on Step 3 patient-safety items.

Postpartum reclassification — universally required:

Long-term reclassification:

Future pregnancy planning:

Complications and Adverse Outcomes

— Preeclampsia (2-fold increase) — check BP and urine protein at every visit.

— Polyhydramnios → preterm labor, malpresentation, cord prolapse.

— Cesarean delivery (higher rates due to macrosomia, failed induction).

— Operative vaginal delivery complications.

— Postpartum hemorrhage from uterine atony with overdistension.

— Infection (wound, endometritis) — hyperglycemia impairs immunity.

— Future T2DM (~50% in 10 years), metabolic syndrome, cardiovascular disease.

— Macrosomia (BW ≥4000 or 4500 g) — driven by fetal hyperinsulinemia from maternal hyperglycemia (Pedersen hypothesis); deposits truncal fat → disproportionate growth with abdominal circumference > head.

— Shoulder dystocia and brachial plexus injury (Erb-Duchenne palsy), clavicular fracture.

— Birth asphyxia from prolonged or obstructed labor.

— Stillbirth — risk rises after 39–40 weeks in poorly controlled GDM.

— Sudden unexplained intrauterine fetal demise in poorly controlled DM.

— Cardiomyopathy (interventricular septal hypertrophy) — reversible, usually asymptomatic; more common with pregestational DM.

— Hypoglycemia (most common) — from abrupt loss of maternal glucose supply with persistent hyperinsulinemia; treat with early feeding ± IV dextrose.

— Hyperbilirubinemia (polycythemia from chronic relative hypoxia → increased red cell turnover).

— Hypocalcemia, hypomagnesemia.

— Respiratory distress syndrome — hyperinsulinemia delays surfactant production even at term-equivalent age.

— Polycythemia (Hct >65%) — risk of stroke, NEC; partial exchange if symptomatic.

— Childhood obesity, glucose intolerance, metabolic syndrome, possibly neurodevelopmental effects.

Key distinction: Congenital malformations (cardiac, NTD, caudal regression, situs inversus) are features of pregestational diabetes, not GDM, because organogenesis is complete before GDM develops. A neonate with VSD whose mother "had GDM" → strongly consider undiagnosed pregestational diabetes.

Maternal complications:

Fetal complications:

Neonatal complications:

Long-term offspring outcomes:

When to Escalate Care — Consults, Inpatient Triage, and ICU

— Maternal-fetal medicine (MFM) consult for:

— Pregestational DM, early-diagnosed GDM with A1c ≥6.5%, GDMA2 requiring high insulin doses (>1.5 U/kg/day), prior stillbirth, suspected fetal anomalies, growth restriction.

— Endocrinology for refractory hyperglycemia, complex insulin pump management.

— Registered dietitian within 1 week of diagnosis (mandatory).

— Diabetes educator for SMBG technique, insulin administration.

— Ophthalmology if reclassified as overt DM (1st trimester baseline).

— Anesthesia consult late pregnancy for high BMI or anticipated difficult airway.

— DKA (can occur at lower glucose in pregnancy — euglycemic DKA with glucose <200 due to expanded plasma volume).

— Severe hyperglycemia (>300 sustained) unresponsive to outpatient titration.

— Severe preeclampsia, HELLP.

— Nonreassuring fetal testing requiring inpatient evaluation/delivery.

— Preterm labor in poorly controlled GDM (steroids will worsen glycemia — admit for IV insulin titration).

— Inability to manage at home (food insecurity, no glucometer access, mental health crisis).

— DKA with hemodynamic instability, AMS, or fetal distress → MICU or labor and delivery ICU per institution.

— Severe preeclampsia/eclampsia with end-organ failure.

— Triggers: infection, hyperemesis, steroids, β-mimetics (terbutaline), insulin nonadherence.

— Manage with IV fluids, IV insulin drip, K+ repletion, treat underlying cause.

— Continuous fetal monitoring — fetal heart tracing typically improves as maternal acidosis resolves; resist urge to deliver during acidosis unless persistent nonreassuring tracing after correction.

CCS pearl: Pregnant patient with N/V, glucose 220, anion gap 22, ketones positive → admit, IV NS, IV insulin drip, K+ repletion, continuous fetal monitoring, obstetric consult. Do not proceed to emergent C-section based on the fetal tracing alone until acidosis is corrected.

Outpatient escalations:

Indications for inpatient admission:

ICU triage:

DKA in pregnancy — key Step 3 points:

Key Differentials — Glucose Abnormalities in Pregnancy

— First identified at early pregnancy screen (<20 wks) with fasting ≥126, random ≥200, A1c ≥6.5%, or 2-hr 75 g OGTT ≥200.

— Implies hyperglycemia at conception → congenital anomaly risk (cardiac, NTD, caudal regression).

— Management: insulin (preferred), fetal echo at 20–22 wks, ophthalmology in 1st trimester, baseline renal function.

— Known history; typically lean, often on pump.

— Higher DKA risk, brittle control.

— Watch for insulin requirements falling unexpectedly in 3rd trimester (placental insufficiency, demise).

— Young, lean patient, strong autosomal-dominant family history of mild early-onset diabetes, negative autoantibodies.

— GCK-MODY (MODY2): mild fasting hyperglycemia (100–145); fetal management depends on whether fetus inherited the mutation (affected fetus may be normal weight despite "hyperglycemia"; unaffected fetus risks macrosomia if mother is treated aggressively).

— Normal early screen, abnormal 24–28-week screen.

— Onset post-organogenesis → no congenital anomaly excess.

— Transient post–betamethasone for fetal lung maturity; peaks days 2–5; manage with temporary insulin titration.

— Infection, severe illness, surgery — resolves with treatment of underlying cause.

Key distinction: Differentiating GDM from pregestational DM hinges on timing of diagnosis and early-pregnancy labs, not on whether the patient "knew" she was diabetic. An A1c of 6.8% drawn at 10 weeks is overt diabetes, even if labeled "GDM" by the chart — managed differently (anomaly screening, eye exam, tighter targets, earlier delivery considerations).

Within the "abnormal glucose in pregnancy" category, distinguish among:

Pregestational type 2 diabetes mellitus:

Pregestational type 1 diabetes:

MODY (maturity-onset diabetes of the young):

Gestational diabetes (true GDM):

Steroid-induced hyperglycemia:

Stress hyperglycemia:

Key Differentials — Non-Glucose Mimics in Pregnancy

— Lower renal threshold for glucose in pregnancy → dipstick glycosuria with normal blood glucose.

— Diagnose by normal GCT/OGTT; reassure.

— Polyuria, polydipsia, but euglycemic; serum sodium often elevated.

— Caused by placental vasopressinase degrading vasopressin; treat with desmopressin (resistant to vasopressinase).

— Twin-twin transfusion, fetal anomalies (esophageal/duodenal atresia → "double bubble"; anencephaly), fetal hydrops, congenital infection (parvovirus, CMV).

— Workup: detailed US, MCA Doppler for anemia, TORCH/parvovirus serologies.

— Both parents large, prior normoglycemic large babies, normal OGTT. No intervention needed.

— Macrosomia, macroglossia, omphalocele, neonatal hypoglycemia — mimics infant of diabetic mother; mother is euglycemic.

— Tachycardia, weight loss, heat intolerance, mild glucose intolerance; check TSH, free T4; differentiate from hyperemesis-associated transient hyperthyroidism.

— Rare in pregnancy; new striae, central obesity, hypertension, hyperglycemia; consider if features atypical.

— Paroxysmal HTN with hyperglycemia, headache, palpitations; high maternal mortality if undiagnosed; plasma metanephrines are the test.

— Hypertriglyceridemia or gallstones; presents with abdominal pain + hyperglycemia.

Board pearl: A pregnant woman with polyuria/polydipsia but normal glucose and elevated serum sodium does not have GDM — think gestational diabetes insipidus, treat with desmopressin (DDAVP), not insulin. This is a classic Step 3 lookalike.

Conditions that mimic GDM presentations (glycosuria, polyuria, large-for-dates uterus, fetal macrosomia) but are not GDM:

Renal glycosuria:

Diabetes insipidus of pregnancy:

Polyhydramnios from non-diabetic causes:

Constitutional macrosomia / familial large baby:

Beckwith-Wiedemann syndrome (fetal):

Hyperthyroidism in pregnancy:

Cushing's syndrome:

Pheochromocytoma:

Acute pancreatitis in pregnancy:

Postpartum Plan, Discharge, and Long-Term Secondary Prevention

— Discontinue insulin/orals at placental delivery.

— Check fasting glucose during admission; if persistently elevated → treat as new T2DM.

— Encourage breastfeeding — reduces maternal T2DM progression by ~50% and lowers offspring obesity risk.

— Contraception counseling before discharge.

— None specific to GDM in most cases (no anti-diabetic agents).

— Continue prenatal vitamin during breastfeeding.

— Aspirin 81 mg may continue postpartum for select patients with preeclampsia/CVD risk (individualized).

— 75 g 2-hour OGTT — mandatory.

— BP check, weight, mood screen (EPDS), contraception, lactation support.

— Review delivery experience and outcomes.

— Repeat glucose screening every 1–3 years if normal postpartum OGTT.

— Annual screening if prediabetes diagnosed postpartum.

— A1c, BP, lipid panel periodically.

— Achieve and maintain prepregnancy weight by 6–12 months; further loss if BMI ≥25.

— 150 min/week moderate exercise.

— Mediterranean or DASH-style diet.

— Smoking cessation, limit alcohol.

— Metformin reduces progression to T2DM in women with prior GDM by ~40% (Diabetes Prevention Program data) — particularly in BMI ≥35, age <60.

— Intensive lifestyle intervention reduces progression by ~50%.

— All methods acceptable in women with prior GDM and no vascular disease.

— In overt DM with vascular complications, avoid combined estrogen-containing methods; prefer progestin-only or LARC (IUD).

— Plan interpregnancy interval ≥18 months with preconception A1c <6.5%.

Step 3 management: A 6-week postpartum GDM patient with OGTT showing fasting 110 and 2-hour 165 (prediabetes) and BMI 33 — best management is intensive lifestyle modification + consider metformin, annual screening, breastfeeding support, and LARC counseling.

Immediate postpartum (delivery hospitalization):

Discharge medications:

4–12 week postpartum visit:

Long-term surveillance (lifelong):

Lifestyle secondary prevention:

Pharmacologic prevention of T2DM (in postpartum patients with prediabetes):

Contraception:

Follow-Up, Monitoring, and Counseling

— GDMA1: prenatal visits every 2 weeks after diagnosis until 36 wks, then weekly; SMBG log review; growth US at 32–36 wks.

— GDMA2: weekly visits after starting medication for dose titration; twice-weekly NSTs from 32 wks; growth US at 32 and 36 wks; insulin adjustment by 10–20% every 3–7 days based on patterns.

— >30% of values above target in any time slot → escalate.

— Pattern recognition:

— Fasting high → adjust bedtime basal.

— Pre-lunch high → adjust breakfast bolus or morning basal.

— Bedtime high → adjust dinner bolus.

— Identify dietary triggers (juice, rice portions) before adding medication.

— Self-monitoring technique; rotate fingerstick sites.

— Recognition and treatment of hypoglycemia (Rule of 15).

— Sick-day rules — continue insulin, hydrate, check ketones if glucose >200.

— Fetal kick counts daily from 28 wks.

— Warning signs requiring immediate evaluation: decreased fetal movement, severe headache, visual changes, RUQ pain, contractions.

— Initiate early; breastfeeding lowers maternal glucose, supports postpartum weight loss, and reduces offspring obesity.

— Insulin and metformin are compatible with breastfeeding.

— Higher hypoglycemia risk during breastfeeding sessions if still on insulin — eat carbs before feeds.

— Screen for depression and anxiety with EPDS at diagnosis, 3rd trimester, and postpartum — GDM diagnosis raises perinatal depression risk.

— Address treatment burden (4 fingersticks/day, dietary restriction, insulin stigma).

CCS pearl: Don't forget to schedule the 4–12-week postpartum 75 g OGTT before discharge — sets up the system-of-care closure. Missing this is a quality measure failure increasingly tested as health-systems content on Step 3.

In-pregnancy follow-up cadence:

Glucose log review — what to look for:

Patient counseling elements (high yield):

Lactation counseling:

Psychosocial support:

Group prenatal care (Centering Pregnancy) — improves GDM outcomes in some studies; offer when available.

Ethical, Legal, and Patient Safety Considerations

— Discuss insulin vs metformin/glyburide: insulin is first-line and does not cross placenta; orals are alternatives with crossing and long-term offspring data still evolving. Document patient preference and reasoning.

— Scheduled cesarean for macrosomia: counsel that EFW has ~15% error, and that prophylactic cesarean for EFW ≥4500 g in GDM (≥5000 g without DM) is offered, not mandated. Respect patient autonomy.

— Patient refusing insulin despite GDMA2 indications: explore reasons (cost, needle fear, language), offer metformin as alternative, document risks discussed (macrosomia, shoulder dystocia, stillbirth). Coercion is not appropriate; ongoing engagement and harm reduction are.

— Refusal of cesarean for macrosomia: document detailed counseling; cannot force surgery on a competent adult.

— Use professional medical interpreters, not family members (especially not children), for sensitive medical decisions and informed consent. Documented as a patient-safety standard.

— GDM disproportionately affects racial/ethnic minorities; access to glucometers, insulin, dietitians is uneven.

— Connect patients with WIC, SNAP, manufacturer assistance programs for insulin/supplies — relevant to value-based care domains.

— Postpartum follow-up gap: ~50% of women with GDM never complete postpartum OGTT. Schedule the OGTT before delivery discharge, send patient with the lab order in hand, and arrange a 4–6 week visit reminder.

— Hand-off between obstetrician and primary care: ensure PCP receives GDM history and recommended long-term screening interval.

— Adolescent pregnant patients have variable state laws on confidentiality for prenatal care; know your jurisdiction.

— Insulin is a high-alert medication — double-check doses, especially during steroid courses and labor; standardized order sets reduce error.

— GDM itself is not reportable, but suspected intimate partner violence discovered during pregnancy assessment requires safety planning and may trigger reporting depending on state law.

Board pearl: The single highest-yield patient-safety quality measure for GDM is completion of postpartum glucose testing. If the question asks "what could most improve this patient's long-term outcomes?" — order the postpartum OGTT and arrange PCP follow-up.

Informed consent and shared decision-making:

Refusal of recommended care:

Cultural humility and language access:

Health disparities:

Transition-of-care risks (Step 3 favorite):

Confidentiality:

Medication safety:

Mandatory reporting:

High-Yield Associations and Rapid-Fire Facts

— GDMA1, controlled: 40 0/7–40 6/7 wks

— GDMA2, controlled: 39 0/7–39 6/7 wks

— Poorly controlled: 37 0/7–38 6/7 wks

Board pearl: A GDM patient on insulin whose insulin requirements suddenly drop in the third trimester — concern for placental insufficiency, preeclampsia, or fetal demise. Order NST and labs immediately; don't just lower the insulin dose.

Pedersen hypothesis: maternal hyperglycemia → fetal hyperglycemia → fetal hyperinsulinemia → macrosomia, neonatal hypoglycemia, organomegaly.

First-line pharmacotherapy: insulin (does not cross placenta).

GDM screen: 1-hour 50 g GCT at 24–28 weeks (non-fasting); ≥140 → 3-hour 100 g OGTT (fasting).

Diagnostic criteria (Carpenter–Coustan, mg/dL): F ≥95, 1h ≥180, 2h ≥155, 3h ≥140 — ≥2 abnormal = GDM.

One-step 75 g OGTT thresholds: F ≥92, 1h ≥180, 2h ≥153 — any one positive.

Glucose targets in pregnancy: F <95, 1h PP <140, 2h PP <120.

Postpartum testing: 75 g 2-hour OGTT at 4–12 weeks.

Lifetime T2DM risk after GDM: ~50% within 10 years.

Recurrence risk in next pregnancy: ~30–50%.

Delivery timing:

EFW threshold for offering elective C-section: ≥4500 g in GDM (≥5000 g without DM).

Steroid effect on glucose: rises for ~5–7 days after betamethasone; preemptively increase insulin.

Euglycemic DKA can occur in pregnancy at glucose <200 — anion gap + ketones drive diagnosis.

Neonatal complications mnemonic — "Big Baby Has Problems": macrosomia, hypoglycemia, hyperbilirubinemia, polycythemia, hypocalcemia, RDS, cardiomyopathy.

Anomalies = pregestational diabetes, not GDM.

Aspirin 81 mg from 12–16 weeks for preeclampsia prevention in GDM + comorbidities (HTN, CKD, prior preeclampsia, multifetal gestation).

Breastfeeding halves maternal T2DM progression; encouraged in all.

Metformin postpartum reduces T2DM progression ~40% in high-risk women with prediabetes.

Post-bariatric patients: use SMBG-based diagnosis, not OGTT (dumping).

Board Question Stem Patterns

— 32-year-old G2P1 with BMI 33, prior 4.4 kg infant, family history of T2DM presenting at 10 weeks → answer: screen at first visit (don't wait until 24–28 wks).

— Routine 24–28 week screen → 1-hour 50 g GCT (non-fasting). Fasting overnight is a distractor.

— 1-hour 50 g = 165 mg/dL → next step is 3-hour 100 g OGTT. If the 1-hour is ≥200, many institutions diagnose without 3-hour.

— New GDM, no severe hyperglycemia → MNT + exercise + SMBG, NOT immediate insulin.

— 2 weeks of diet, persistent fasting 102 mg/dL → add bedtime NPH or detemir. Match the abnormal time to the regimen.

— Isolated postprandial elevations after lunch → rapid-acting (aspart/lispro) before lunch.

— Patient asks about glyburide → counsel that insulin is first-line, crosses placenta less, fewer neonatal complications.

— Neonate with cardiac defect and "history of maternal GDM" → underlying issue is likely undiagnosed pregestational diabetes.

— EFW 4600 g at 38 wks in GDM → offer scheduled cesarean.

— GDMA2 in active labor → hold subQ insulin, IV glucose + insulin drip, q1h glucose checks.

— 6 wks postpartum GDM follow-up → 75 g 2-hour OGTT (not A1c alone, not "no testing").

— Postpartum prediabetes after GDM → lifestyle + consider metformin.

— 3rd-trimester woman with N/V, glucose 195, AG 22, ketones → DKA; admit, IV fluids, IV insulin, K+, fetal monitoring.

— Sudden 30% fall in insulin needs at 36 wks → evaluate fetal well-being and placental function.

Step 3 management: When a stem gives a "best next step," ask: is the patient screened, diagnosed, on MNT, on insulin, in labor, or postpartum? The answer almost always corresponds to the next sequential step in this longitudinal algorithm, not a leap forward.

Pattern 1 — When to screen early:

Pattern 2 — Screening test choice:

Pattern 3 — Diagnostic algorithm:

Pattern 4 — Initial management after diagnosis:

Pattern 5 — When to escalate to insulin:

Pattern 6 — Choice of insulin pattern:

Pattern 7 — Drug safety:

Pattern 8 — Anomaly distinction:

Pattern 9 — Macrosomia/cesarean:

Pattern 10 — Intrapartum:

Pattern 11 — Postpartum testing:

Pattern 12 — Long-term prevention:

Pattern 13 — Euglycemic DKA:

Pattern 14 — Insulin requirement drop:

One-Line Recap

— Screen early if BMI ≥25 plus risk factor, prior GDM, A1c ≥5.7%, or high-risk ethnicity; then again at 24–28 weeks regardless.

— Match the insulin regimen to the abnormal glucose pattern — bedtime basal for fasting hyperglycemia, prandial rapid-acting for postprandial spikes.

— GDM does not cause congenital anomalies — anomalies imply pregestational diabetes (early A1c ≥6.5% or fasting ≥126).

— Close the loop: postpartum 75 g OGTT at 4–12 weeks, lifelong screening every 1–3 years, breastfeeding and lifestyle, metformin for postpartum prediabetes — this is the Step 3 transition-of-care moneyball.

— Persistent fasting ≥95 or postprandial above target × 1–2 weeks → start insulin.

— EFW ≥4500 g in GDM → offer scheduled cesarean.

— Insulin requirements drop late pregnancy → evaluate fetus and placenta urgently.

Board pearl: If you remember nothing else: insulin is first-line, MNT precedes pharmacotherapy, deliver GDMA2 at 39 weeks, and never let a GDM patient leave postpartum without a 75 g 2-hour OGTT scheduled — these four anchors will resolve the majority of Step 3 GDM vignettes.

Bottom line: Gestational diabetes is universally screened at 24–28 weeks with a 1-hour 50 g GCT (or 1-step 75 g OGTT), diagnosed by Carpenter–Coustan after a 3-hour 100 g OGTT, treated first with medical nutrition therapy and exercise then insulin if glucose targets (fasting <95, 1h PP <140, 2h PP <120) are not met, surveilled with growth ultrasound and NSTs in GDMA2, delivered at 39–40 weeks based on control, and always re-screened with a 75 g 2-hour OGTT at 4–12 weeks postpartum because of the ~50% lifetime T2DM risk.

Four high-yield recaps:

Three management triggers to memorize: