Endocrine

Gestational diabetes: screening and management

Clinical Overview and When to Suspect Gestational Diabetes

— Pregnancy is a state of progressive insulin resistance peaking at 24–28 weeks

— GDM occurs when β-cell reserve cannot compensate

— Reflects underlying β-cell dysfunction → ~50% lifetime risk of T2DM

— Universal screening at 24–28 weeks for all pregnant patients without preexisting diabetes (ACOG, USPSTF Grade B)

— Early screening at first prenatal visit (<15 weeks) if risk factors: BMI ≥25 (≥23 if Asian), prior GDM, prior macrosomic infant (≥4000 g), PCOS, 1st-degree relative with DM, HbA1c ≥5.7%, prior IGT/IFG, high-risk ethnicity, prior stillbirth, HTN, CVD, physical inactivity

— Repeat at 24–28 weeks if early screen negative

— Fasting glucose ≥126, random ≥200, or HbA1c ≥6.5% at initial visit = pregestational/overt DM, not GDM

— Implications differ: overt DM carries congenital anomaly risk; GDM does not (onset post-organogenesis)

Key distinction: GDM diagnosed in 2nd/3rd trimester is not associated with congenital malformations because hyperglycemia develops after organogenesis (>10 weeks). Anomaly risk applies only to pregestational or early-detected overt DM. This drives the Step 3 distinction between ordering a fetal echo (overt DM) vs. standard anatomy ultrasound (GDM). Recognize the difference on stems mentioning A1c at intake vs. 28-week OGTT.

Definition: Gestational diabetes mellitus (GDM) is glucose intolerance with onset or first recognition during pregnancy, typically emerging in the 2nd–3rd trimester as placental hormones (human placental lactogen, cortisol, progesterone) drive insulin resistance.

Epidemiology: Affects ~6–9% of US pregnancies; rising with obesity, advanced maternal age, and ethnic shifts (higher in Hispanic, South/East Asian, Native American, African American populations).

Pathophysiology:

When to suspect / screen:

Distinguishing from overt diabetes in pregnancy:

Presentation Patterns and Key History

— Prior GDM (recurrence ~40–60%)

— Prior macrosomic infant (≥4000 g, or shoulder dystocia, birth injury)

— Prior unexplained stillbirth, congenital anomaly, or polyhydramnios

— PCOS, acanthosis nigricans, prior IGT, metabolic syndrome

— Family history of T2DM in 1st-degree relative

— Ethnicity (Hispanic, South Asian, Native American, Pacific Islander, African American)

— Pre-pregnancy BMI, gestational weight gain trajectory

— Medications: chronic glucocorticoids, atypical antipsychotics, β-agonists (terbutaline), HIV antiretrovirals

— Fundal height >gestational age by 3+ cm

— Polyhydramnios on ultrasound (AFI >24 or DVP >8)

— Macrosomia / large-for-gestational-age fetus on growth ultrasound

— Recurrent UTI or candidiasis

Board pearl: A woman with BMI 32, prior 4.2 kg infant, and PCOS presenting at her first prenatal visit (8 weeks) gets early GDM screening now, not at 24–28 weeks. If negative, she still gets repeat screening at 24–28 weeks. Step 3 stems love testing this two-step early/late screening logic.

Step 3 management: Document risk factors at the first prenatal visit and stratify screening timing. In ambulatory OB practice, missed early screening in a high-risk patient is a common quality-improvement target — the EMR should flag BMI ≥25 + risk factor combinations to trigger an early 75g or 50g screen order.

Typical presentation: GDM is asymptomatic — discovered on routine 24–28 week screening. Stems rarely show classic polyuria/polydipsia.

High-yield history elements to elicit:

Symptoms when present (uncommon): polyuria, polydipsia, recurrent vulvovaginal candidiasis, fatigue. New-onset symptoms in 3rd trimester should prompt fingerstick glucose.

Obstetric findings suggesting undiagnosed GDM:

Prior pregnancy outcomes that increase suspicion: shoulder dystocia, neonatal hypoglycemia, NICU admission for "big baby," Erb's palsy in prior infant.

Physical Exam Findings and Maternal-Fetal Assessment

— BMI and gestational weight gain (IOM targets: 25–35 lb if normal BMI; 15–25 lb overweight; 11–20 lb obese)

— Acanthosis nigricans at neck, axillae — marker of insulin resistance

— Skin tags

— Blood pressure (screen for coexisting gestational HTN/preeclampsia — strongly associated with GDM)

— Fundoscopic exam if pregestational DM suspected (not routinely in GDM)

— Thyroid exam (autoimmune comorbidity if T1DM suspected)

— Fundal height — measure each visit after 20 weeks; >3 cm above gestational age → ultrasound for macrosomia or polyhydramnios

— Leopold maneuvers in 3rd trimester to estimate fetal size and presentation

— Fetal heart tones (baseline)

— Detailed anatomy scan at 18–20 weeks (standard, not enhanced unless overt DM)

— Growth ultrasound at 32–36 weeks to assess macrosomia and AFI

— Antenatal testing (NST ± AFI or BPP) weekly or twice weekly from 32 weeks if on medication or poorly controlled; for diet-controlled well-managed A1GDM, testing often begins 36–39 weeks per local protocol

— BP ≥140/90 + proteinuria → preeclampsia workup

— Decreased fetal movement → immediate NST

— Rapid fundal growth → polyhydramnios assessment

Key distinction: A1GDM (diet-controlled) vs A2GDM (requires pharmacotherapy) drives the intensity of antenatal surveillance and delivery timing. A2GDM patients get earlier and more frequent fetal testing and earlier delivery (39 weeks vs. up to 40w6d for well-controlled A1GDM). Step 3 stems often hinge on whether the patient is "on insulin" — that flips the management pathway.

Maternal exam is typically unremarkable in GDM — diagnosis is biochemical. Findings, when present, reflect insulin resistance or complications.

Maternal findings to document:

Obstetric exam:

Fetal assessment milestones in GDM:

Signs of complications to look for:

Diagnostic Workup — Screening Tests (One-Step vs Two-Step)

— Step 1: 50 g glucose challenge test (GCT), non-fasting, 1-hour plasma glucose

· ≥140 mg/dL → proceed to Step 2 (some use ≥130 or ≥135 for higher sensitivity)

· ≥200 mg/dL on GCT alone is often treated as diagnostic of GDM without OGTT

— Step 2: 100 g 3-hour OGTT, fasting

· Carpenter-Coustan thresholds: Fasting ≥95, 1h ≥180, 2h ≥155, 3h ≥140 mg/dL

· ≥2 abnormal values = GDM

· 1 abnormal value = impaired glucose tolerance; some clinicians treat as GDM-lite with nutrition counseling

— 75 g 2-hour OGTT, fasting

— Any single abnormal value diagnoses GDM:

· Fasting ≥92, 1h ≥180, 2h ≥153 mg/dL

— Identifies more cases but increases diagnosis rates 2–3×

— Universal screen at 24–28 weeks

— Early screen (<15 weeks) for high-risk patients using same thresholds; if negative, repeat at 24–28 weeks

— HbA1c, fasting glucose, or random glucose to detect overt/pregestational DM

· A1c ≥6.5%, FPG ≥126, or random ≥200 with symptoms = overt DM

— Urinalysis (glycosuria, proteinuria baseline)

— Recent corticosteroids (betamethasone for fetal lung maturity) transiently elevate glucose — defer screening 5–7 days

— Acute illness, prolonged fasting <8h, or carbohydrate restriction <150 g/day for 3 days pre-test can skew OGTT

Board pearl: Two abnormal values on the 100 g 3-hour OGTT = GDM. One abnormal value does not formally meet criteria but warrants nutrition counseling and possible repeat. Memorize 95/180/155/140 (Carpenter-Coustan) — these are recurring Step 3 numbers.

Two-Step Approach (ACOG-preferred in US):

One-Step Approach (IADPSG / ADA-acceptable):

Timing:

Initial visit labs (all pregnant patients):

Pitfalls:

Diagnostic Workup — Glycemic Monitoring and Confirmatory Assessment

— 4 checks daily: fasting + 1-hour or 2-hour postprandial after each meal

— Targets (ACOG/ADA):

· Fasting <95 mg/dL

· 1-hour postprandial <140 mg/dL

· 2-hour postprandial <120 mg/dL

— Log values; review weekly initially, then biweekly

— Less useful for ongoing management due to physiologic decrease in pregnancy (increased RBC turnover)

— Goal <6% in pregnancy if used; <5.7% ideal

— Useful at diagnosis to rule out overt DM

— Increasingly used, especially in A2GDM and pregestational DM (CONCEPTT trial supports CGM in T1DM pregnancy)

— Target time-in-range (63–140 mg/dL) >70%

— TSH (overlap with thyroid disease in pregnancy)

— Baseline creatinine, urine protein/creatinine ratio (preeclampsia baseline)

— Lipid panel if not already done (cardiovascular risk stratification postpartum)

— Growth ultrasound at 32–36 weeks (estimated fetal weight, AFI, abdominal circumference)

— NST ± AFI or biophysical profile per A1 vs A2 classification

— Doppler studies if IUGR (uncommon in GDM, suggests vascular pregestational DM)

— 75 g 2-hour OGTT at 4–12 weeks postpartum — required for every GDM patient

— Classify as normal, IFG, IGT, or overt T2DM

— Then lifelong screening every 1–3 years with FPG, A1c, or 75g OGTT

Step 3 management: The 4–12 week postpartum 75g OGTT is a Step 3 favorite — it is not optional. It's a measurable quality metric and missing it is a common ambulatory transitions-of-care failure tested in stems about "what should be ordered at the postpartum visit."

Once diagnosed, initiate self-monitoring of blood glucose (SMBG):

HbA1c in GDM:

Continuous glucose monitoring (CGM):

Additional labs at GDM diagnosis:

Fetal surveillance studies:

Postpartum confirmatory testing:

Risk Stratification and First-Line Management Logic

— A1GDM (diet-controlled): glycemic targets met with medical nutrition therapy (MNT) + exercise alone

— A2GDM: requires pharmacotherapy (insulin or oral agent) to meet targets

— Step 1: Lifestyle for 1–2 weeks

· Referral to registered dietitian for MNT

· Carbohydrate-controlled diet: ~175 g/day minimum, 40–45% carbs, complex/low-GI, split across 3 meals + 2–3 snacks

· Caloric goals: ~30 kcal/kg (normal BMI), 25 kcal/kg (overweight), 12–15 kcal/kg (obese)

· Exercise: 30 min moderate activity (walking, swimming) most days unless contraindicated

— Step 2: SMBG review

· If ≥30% of values out of target over 1–2 weeks, or any single fasting >105 or postprandial >160 → start pharmacotherapy

— Step 3: Initiate insulin (first-line) or metformin/glyburide (if patient declines insulin)

— Initial fasting glucose ≥110 at diagnosis

— HbA1c ≥6.5% at diagnosis

— Fetal abdominal circumference >75th percentile on growth ultrasound (marker of fetal hyperinsulinism)

— Every 1–2 weeks until well-controlled, then every 2–4 weeks

— Increase frequency to weekly in 3rd trimester or if on insulin

CCS pearl: On a Step 3 CCS case, after diagnosing GDM, the immediate orders are: (1) Nutrition consult / dietitian referral, (2) Glucometer and test strips with SMBG education, (3) Glucose log, (4) Schedule follow-up in 1–2 weeks, (5) Growth ultrasound at 32–36 weeks, (6) Continue prenatal vitamins. Advancing the clock 2 weeks and reviewing the log is the next move — don't jump to insulin without giving lifestyle a chance unless initial glucoses are markedly elevated.

Classification drives management intensity:

Stepwise management algorithm:

Factors prompting earlier pharmacotherapy:

Visit cadence:

Pharmacotherapy — Insulin as First-Line and Dosing Strategy

— Elevated fasting only → bedtime NPH or detemir (long-acting)

— Elevated postprandial only → rapid-acting (lispro, aspart) before meals

— Both elevated → basal-bolus: NPH/detemir + rapid-acting prandial

— Total daily dose ~0.7–1.0 units/kg/day in 3rd trimester (lower in 1st, increases through pregnancy)

— Split: 50% basal, 50% prandial (divided across meals)

— Example: 80 kg patient at 28 weeks: TDD ~0.8 × 80 = 64 units; 32 basal (16 AM NPH + 16 PM NPH or all bedtime), 32 prandial (~10 units before each meal)

— Rapid: lispro, aspart (both pregnancy-tested, FDA Category B equivalent)

— Basal: NPH (most data), detemir (Category B), glargine (acceptable, U-100 only)

— Avoid: glulisine and degludec (less pregnancy data)

— Metformin: crosses placenta; reasonable alternative when insulin refused or inaccessible; up to 40% require add-on insulin

— Glyburide: crosses placenta in small amounts, associated with neonatal hypoglycemia and macrosomia in some studies; no longer recommended as first-line oral by ACOG/ADA

— Counsel that long-term offspring data on oral agents are limited

— Adjust insulin every 3–7 days based on glucose log

— Increase dose by 10–20% per adjustment for persistently out-of-range values

— Insulin requirements rise through 3rd trimester, then drop sharply at delivery (placenta removed)

Board pearl: A patient whose only abnormal value is fasting glucose 105 gets bedtime NPH, not prandial insulin. Match the insulin to the glucose pattern — Step 3 loves this discrimination.

Insulin is first-line pharmacotherapy in GDM (ACOG, ADA) — does not cross placenta, most predictable, gold standard.

Choosing insulin based on glucose pattern:

Starting doses (weight-based):

Preferred insulins in pregnancy:

Oral agents — when used:

Titration:

Procedures and Delivery Management

— A1GDM, well-controlled: expectant management to 40w6d; deliver by 41 weeks

— A2GDM, well-controlled on medication: deliver 39w0–39w6d

— A2GDM, poorly controlled: individualized, often 37w0–38w6d

— Suspected macrosomia (EFW ≥4500 g in GDM): offer scheduled cesarean to reduce shoulder dystocia/brachial plexus injury

— Betamethasone for fetal lung maturity if delivery <37 weeks anticipated

— Expect transient hyperglycemia for 3–5 days — admit or intensify monitoring; may need IV insulin infusion

— Target maternal glucose 70–110 mg/dL (some say 70–125) during labor to minimize neonatal hypoglycemia

— Check glucose every 1–2 hours in labor

— A1GDM: usually no insulin needed intrapartum

— A2GDM on insulin: hold long-acting morning of induction/C-section; start D5-containing IVF + insulin drip if glucose >110

— Scheduled C-section: hold insulin morning of surgery

— Discontinue all GDM medications immediately after delivery

— Check fasting glucose on postpartum day 1–2 to confirm resolution

— If glucose remains elevated → likely overt/pregestational DM, transition to T2DM management

— Heel-stick glucose at 30 min and every 2–3 hours × first 12–24 h

— Treat neonatal hypoglycemia (<40 mg/dL) with feeds or IV dextrose

— Watch for polycythemia, hyperbilirubinemia, hypocalcemia, respiratory distress

CCS pearl: For an A2GDM patient on insulin admitted for induction at 39 weeks: (1) Hold AM insulin, (2) Start D5 ½NS + insulin infusion protocol, (3) Q1–2h fingerstick glucose, (4) Continuous fetal monitoring, (5) Pediatrics on standby for neonatal hypoglycemia, (6) Discontinue insulin postpartum, (7) Encourage breastfeeding.

Delivery timing (ACOG):

Antenatal corticosteroids:

Intrapartum glucose management:

Immediate postpartum:

Neonatal care:

Special Populations — Renal/Hepatic Impairment and Older Gravidas

— Higher GDM risk; offer early screening

— Higher baseline preeclampsia, chromosomal anomaly, and stillbirth risk — integrate with cell-free DNA, anatomy scan

— Lower threshold for antenatal testing

— Pre-existing CKD or diabetic nephropathy → higher risk for preeclampsia, IUGR, preterm delivery

— In GDM specifically, renal disease is uncommon; suspect pregestational DM if proteinuria present at diagnosis

— Metformin contraindicated if eGFR <30, caution 30–45 (use insulin)

— Insulin dose may need reduction with significant CKD (renal insulin clearance decreased)

— Glyburide and metformin generally avoided in significant liver disease

— Insulin is safe — no hepatic adjustment

— Distinguish acute fatty liver of pregnancy and HELLP (transaminitis, thrombocytopenia, hemolysis) from incidental LFT abnormalities — these are obstetric emergencies, not GDM complications

— Higher insulin requirements (often 1.5–2 units/kg/day in 3rd trimester)

— Concentrated insulin (U-500) rarely needed

— Bariatric surgery history: avoid OGTT (dumping syndrome); use SMBG-based monitoring with fasting + postprandial fingersticks for 1 week at 24–28 weeks

— Higher GDM incidence; same screening

— Caloric needs higher; tighter glycemic surveillance

— Anticipate steroid-induced hyperglycemia; have insulin sliding scale ready

Key distinction: Proteinuria at GDM diagnosis suggests pre-existing diabetic nephropathy / pregestational DM, not new GDM. Reclassify the patient and intensify surveillance for preeclampsia, IUGR, and fetal anomalies. Order fetal echocardiography and a 1st-trimester A1c retrospectively if available.

Advanced maternal age (≥35):

Renal impairment in pregnancy:

Hepatic impairment:

Obesity (BMI ≥30):

Multiple gestation:

Glucocorticoid exposure (asthma, autoimmune, preterm labor):

Special Populations — Postpartum, Lactation, and Future Pregnancies

— Stop all glucose-lowering medications at delivery

— Encourage early breastfeeding — reduces neonatal hypoglycemia and maternal future T2DM risk

— Skin-to-skin contact and feeding within 1 hour of birth

— Insulin: safe; doesn't transfer in clinically significant amounts

— Metformin: compatible with breastfeeding; minimal milk transfer

— Glyburide: compatible; low risk of infant hypoglycemia

— Encourage breastfeeding for ≥6 months; reduces future maternal T2DM by ~50%

— 75 g 2-hour OGTT at 4–12 weeks postpartum

— Interpret with non-pregnant criteria:

· Normal: FPG <100, 2h <140

· IFG: FPG 100–125; IGT: 2h 140–199

· DM: FPG ≥126 or 2h ≥200

— If normal → repeat screening every 1–3 years lifelong with FPG, A1c, or OGTT

— If prediabetes → metformin and/or intensive lifestyle (DPP trial reduces progression by ~50%)

— All methods acceptable; no GDM-specific contraindications

— LARCs (IUD, implant) preferred for spacing and adherence

— Preconception counseling: optimize weight, A1c <6.5% before next pregnancy

— Early GDM screening in subsequent pregnancies (1st trimester)

— Recurrence risk 40–60%

— Childhood obesity, metabolic syndrome, T2DM

— Anticipatory guidance on healthy feeding, activity

Step 3 management: At the 6-week postpartum visit, order the 75g OGTT, screen for postpartum depression (EPDS), discuss contraception, encourage breastfeeding continuation, and document referral to PCP for long-term metabolic surveillance. This is a classic Step 3 ambulatory transitions-of-care question.

Immediate postpartum:

Lactation and medications:

Postpartum screening (mandatory):

Contraception counseling:

Future pregnancy planning:

Offspring risks:

Complications and Adverse Outcomes

— Preeclampsia / gestational HTN — risk doubled in GDM; check BP and urine protein each visit

— Polyhydramnios — fetal osmotic diuresis from hyperglycemia

— Cesarean delivery — higher rate due to macrosomia, failed induction

— Birth trauma — perineal lacerations, postpartum hemorrhage

— Future T2DM — ~50% lifetime risk

— Future cardiovascular disease — 2× risk; GDM is a sex-specific CVD risk enhancer (ACC/AHA)

— Recurrent GDM — 40–60% in next pregnancy

— Macrosomia (≥4000 g) and large-for-gestational-age — from fetal hyperinsulinism (Pedersen hypothesis)

— Shoulder dystocia — risk rises sharply >4500 g; brachial plexus injury (Erb's palsy), clavicular fracture

— Stillbirth — modestly elevated, especially with poor control or post-term

— Polyhydramnios → preterm labor, cord prolapse

— Congenital anomalies only with overt/pregestational DM (cardiac, caudal regression, NTDs), not isolated GDM

— Hypoglycemia (<40 mg/dL) — most common; abrupt loss of maternal glucose with persistent fetal hyperinsulinemia

— Respiratory distress syndrome — delayed surfactant production

— Hyperbilirubinemia, polycythemia — increased erythropoiesis from chronic relative hypoxia

— Hypocalcemia, hypomagnesemia

— Cardiomyopathy — transient septal hypertrophy

— Childhood obesity, T2DM, metabolic syndrome, neurodevelopmental risks

Board pearl: Shoulder dystocia after delivery of the fetal head → McRoberts maneuver first (hyperflexion of maternal hips), then suprapubic pressure. Never apply fundal pressure (worsens impaction). GDM is the classic setup in shoulder dystocia stems.

Maternal complications:

Fetal complications:

Neonatal complications:

Long-term offspring outcomes:

When to Escalate — Inpatient Admission, Consults, MFM Referral

— DKA (rare in GDM, suggests pregestational T1DM) — emergent ICU/obstetric admission

— Severe hyperglycemia with ketonuria

— Severe preeclampsia, HELLP, eclampsia

— Non-reassuring fetal status (recurrent late decelerations, absent/reversed UA Doppler)

— Antenatal steroid administration with insulin titration in poorly controlled A2GDM

— Labor induction for delivery indication

— Maternal-Fetal Medicine (MFM): poorly controlled A2GDM, fetal growth restriction or macrosomia, recurrent GDM with prior complications, suspected pregestational DM, comorbid HTN/renal disease

— Endocrinology: complex insulin regimens, suspected new T1DM, postpartum overt diabetes

— Registered Dietitian / Diabetes Educator: essential at diagnosis

— Neonatology / Pediatrics: prenatal consult if macrosomia, prematurity, or known anomalies

— Anesthesia: if morbid obesity or anticipated difficult airway/regional anesthesia

— Social work / behavioral health: food insecurity, medication access issues, depression

— Decreased fetal movement → NST

— Severe headache, vision changes, RUQ pain, BP ≥160/110 → preeclampsia workup

— Contractions <37 weeks → preterm labor evaluation

— Glucose >250 with ketonuria → assess for DKA

— Tertiary center if <34 weeks anticipated delivery, NICU level III needed, or maternal critical illness

CCS pearl: On CCS, if a 32-week A2GDM patient presents with BP 162/108, headache, and 2+ proteinuria: (1) Admit to L&D, (2) IV magnesium sulfate for seizure prophylaxis, (3) IV labetalol or hydralazine for severe-range BP, (4) Betamethasone × 2 doses, (5) Anticipate steroid hyperglycemia — insulin infusion, (6) Continuous fetal monitoring, (7) MFM consult, (8) Plan delivery per severity.

Outpatient management is the norm. Escalate when control fails or complications emerge.

Indications for inpatient admission:

Consultations:

Red flags requiring same-day evaluation:

Hospital transfer:

Key Differentials — Other Hyperglycemic States in Pregnancy

— A1c ≥6.5% at first prenatal visit, fasting ≥126, or random ≥200 with symptoms

— Implications: congenital anomaly risk (cardiac, NTDs, caudal regression); needs fetal echo at 20–22 weeks

— Management mirrors A2GDM but with broader systemic screening (retinal exam, urine ACR, lipid panel, TSH)

— Usually known prior; risk for DKA at lower glucose levels in pregnancy

— Requires basal-bolus insulin, CGM strongly recommended

— Higher rates of anomalies, preeclampsia, preterm delivery, IUGR

— Autosomal dominant; mild fasting hyperglycemia in young, lean patient with strong FH across generations

— GCK-MODY: stable mild fasting hyperglycemia (100–145); generally doesn't require treatment unless fetus is unaffected (large fetus)

— Consider genetic testing if family pattern suggests

— From acute illness, infection, glucocorticoids, β-agonists (terbutaline for preterm labor)

— Resolves with treatment of trigger; not GDM

— Suspect if lean, rapid insulin dependence, weight loss; check GAD-65 antibodies

— Rare; consider if refractory hyperglycemia with clinical stigmata

Key distinction: GCK-MODY in pregnancy is uniquely managed by fetal abdominal circumference monitoring, not maternal glucose targets. If fetus inherits GCK mutation, fetal growth is normal despite maternal hyperglycemia — treating mother aggressively can cause IUGR. Step 3 may test this nuance in a stem describing a young, lean, normal-BMI woman with stable fasting hyperglycemia and strong family history.

Pregestational Type 2 DM (undiagnosed):

Pregestational Type 1 DM:

MODY (Maturity-Onset Diabetes of the Young):

Stress hyperglycemia:

LADA (latent autoimmune diabetes in adults):

Cushing syndrome / pheochromocytoma / acromegaly:

Key Differentials — Non-Hyperglycemic Mimics and Cross-System Considerations

— Fetal anomalies: TEF, duodenal atresia (double bubble), anencephaly, cardiac defects

— Twin-to-twin transfusion syndrome

— Fetal anemia (Rh alloimmunization, parvovirus B19)

— Idiopathic (most common)

— Workup: detailed anatomy ultrasound, MCA Doppler, infectious panel

— Constitutional (large parents)

— Excessive gestational weight gain

— Beckwith-Wiedemann syndrome (macroglossia, omphalocele, hyperinsulinism)

— Post-term pregnancy

— Lowered renal glucose threshold in pregnancy is normal

— Doesn't equal GDM; doesn't replace OGTT

— Physiologic (increased GFR)

— Gestational diabetes insipidus — vasopressinase-mediated, 3rd trimester; treat with desmopressin (DDAVP)

— Primary polydipsia

— Common in GDM but also in normoglycemic pregnancy due to glycosuria and immune modulation

— Reactive hypoglycemia, dumping syndrome (post-bariatric), anxiety — not GDM

— Severe transaminitis, thrombocytopenia, hypoglycemia (not hyperglycemia), coagulopathy

— Obstetric emergency; deliver

Board pearl: A 3rd-trimester patient with polyuria/polydipsia, dilute urine, normal glucose, and rapid response to desmopressin has gestational diabetes insipidus from placental vasopressinase — not GDM. Distinguishing the "two diabetes" of pregnancy is a high-yield Step 3 vignette twist.

Conditions that mimic GDM complications or share features:

Polyhydramnios from non-GDM causes:

Macrosomia without GDM:

Glycosuria without GDM:

Polyuria/polydipsia in pregnancy — non-DM causes:

Recurrent UTI / candidiasis:

Postprandial symptoms (palpitations, lightheadedness):

Acute fatty liver of pregnancy / HELLP:

Secondary Prevention, Discharge Plan, and Long-Term Risk Reduction

— Discontinue all glucose-lowering medications

— Check fasting glucose on PPD #1 to confirm resolution

— Encourage breastfeeding and skin-to-skin

— Postpartum depression screening (EPDS) before discharge

— Schedule 6-week postpartum visit with OB

— Schedule 75 g OGTT at 4–12 weeks postpartum

— Provide patient education on long-term T2DM and CVD risks

— 75 g 2-hour OGTT (or arrange immediately if not done)

— BP, weight, BMI

— Contraception plan

— Lactation support

— Mental health (EPDS again)

— Lifestyle reinforcement

— Document referral to primary care

— Lifestyle: Mediterranean or DASH-style diet, ≥150 min/week moderate exercise, target BMI <25, 5–7% weight loss if overweight (DPP-modeled)

— Metformin for women with persistent prediabetes — reduces T2DM progression ~50% (DPP)

— Lifelong T2DM screening every 1–3 years with FPG, A1c, or OGTT

— CVD risk assessment — GDM is recognized as a sex-specific risk enhancer; address lipids, BP, smoking; statin per ASCVD risk if not pregnant/lactating

— Annual blood pressure check — increased lifetime HTN risk

— Preconception A1c <6.5%, optimize weight

— Folic acid 400–800 μg daily (higher if overt DM, BMI ≥30, prior NTD)

— Early GDM screen at next pregnancy

Step 3 management: GDM history changes the lifetime preventive care plan — Step 3 will test whether you order T2DM screening every 1–3 years, counsel on CVD risk, and continue lifestyle reinforcement at every primary care visit. This is value-based, longitudinal care.

Discharge from L&D after GDM delivery:

6-week postpartum visit checklist:

Long-term secondary prevention:

Future pregnancy:

Follow-Up, Monitoring Parameters, and Counseling Cadence

— Visits every 1–2 weeks until controlled, then every 2–4 weeks

— Weekly in 3rd trimester for A2GDM

— SMBG log review every visit

— Growth ultrasound 32–36 weeks

— Antenatal testing (NST/BPP) starting at 32 weeks (A2GDM) or 36–39 weeks (A1GDM)

— BP and urine dipstick each visit (preeclampsia surveillance)

— Weight tracking against IOM targets

— Fasting and postprandial glucose (4 checks/day)

— Fetal kick counts daily from 28 weeks

— Weight weekly at home

— Symptoms: headache, vision changes, RUQ pain, edema, decreased movement → call OB

— PPD #1–2: fasting glucose check

— Week 1–2: in-person or telehealth check-in (BP, mood, feeding)

— Week 4–12: 75 g OGTT

— 6-week comprehensive postpartum visit

— Transition to PCP for long-term diabetes/CVD screening

— Nutrition: portion control, carb counting, plate method, low-glycemic choices

— Activity: 30 min walking daily; postpartum: resume gradually

— Breastfeeding benefits (maternal T2DM reduction, neonatal glycemic stability)

— Future pregnancy planning

— Smoking and alcohol cessation

— Medication adherence and hypoglycemia recognition (if on insulin)

— Symptoms: shakiness, sweating, confusion, palpitations

— Rule of 15: 15 g fast carbs, recheck in 15 min

— Glucagon kit for severe; family/partner training

Board pearl: Documented evidence of postpartum OGTT completion is a Step 3-favorite quality metric. Stems often ask: "What is the most appropriate next step at the 6-week visit for a patient with prior GDM?" — answer is the 75 g 2-hour OGTT, not A1c or fasting glucose alone (lower sensitivity).

During pregnancy after GDM diagnosis:

Patient self-monitoring parameters:

Postpartum follow-up:

Counseling content:

Hypoglycemia education for patients on insulin:

Ethical, Legal, and Patient Safety Considerations

— Discuss insulin vs metformin: insulin is first-line but more burdensome; metformin crosses placenta with limited long-term offspring data — patient must understand trade-offs

— Document shared decision-making, especially for oral agents

— GDM disproportionately affects ethnic minorities; use professional interpreters (not family members) for OGTT instructions, insulin teaching, dietary counseling

— Tailor nutritional counseling to cultural food patterns rather than imposing a generic diet

— Glucometers, test strips, and insulin can be cost-prohibitive

— Screen for food insecurity; refer to WIC, SNAP, community resources

— Verify insurance coverage for diabetes supplies; some Medicaid plans require prior authorization

— Postpartum 75g OGTT completion rates are <40% nationally — a documented quality gap

— Use closed-loop referrals between OB and PCP

— Send postpartum diagnosis and recommendations directly to the receiving PCP

— Schedule the OGTT before hospital discharge

— Insulin error is a top inpatient adverse event; use standardized order sets, weight-based dosing, double-checks on pumps and drips

— Teach all insulin users hypoglycemia recognition and glucagon use; involve family

— Suspected newborn abuse or neglect (e.g., parental noncompliance threatening neonate) → CPS notification

— Substance use disorder in pregnancy: counsel and refer; varies by state (some mandate reporting)

— Adolescent gravidas have specific confidentiality rights regarding pregnancy and STI care; respect state laws

— Be alert to assumptions about adherence based on socioeconomic status; provide equal counseling and access

Step 3 management: The closed-loop OB-to-PCP handoff after GDM is a Step 3-tested patient safety scenario. The correct answer often includes: scheduling the postpartum OGTT before discharge, forwarding records, and ensuring continuity — not simply "advise follow-up with PCP."

Informed consent for GDM treatment:

Cultural and language competence:

Health literacy and access:

Transitions of care — the highest-risk failure point:

Patient safety in hypoglycemia:

Mandatory reporting:

Confidentiality:

Bias and equity:

High-Yield Associations and Rapid-Fire Clinical Facts

Board pearl: Caudal regression syndrome in a stem (sacral agenesis, lower extremity deformities) = pregestational DM, not GDM — flag pregestational status retroactively.

Carpenter-Coustan thresholds (100g 3-hour OGTT): 95 / 180 / 155 / 140 — need ≥2 abnormal for GDM

IADPSG (75g 2-hour OGTT): 92 / 180 / 153 — need ≥1 abnormal

Glycemic targets in pregnancy: Fasting <95, 1h pp <140, 2h pp <120

Postpartum OGTT: 75g 2-hour at 4–12 weeks for every GDM patient

First-line GDM pharmacotherapy: insulin (not metformin, not glyburide)

A1c in pregnancy: target <6%; less reliable due to RBC turnover

Fetal anomalies: only with pregestational/overt DM (organogenesis), not isolated GDM

Classic anomalies in pregestational DM: caudal regression syndrome (pathognomonic), cardiac (TGA, VSD), NTDs, renal agenesis

Macrosomia threshold for elective C-section in GDM: EFW ≥4500 g

Shoulder dystocia first maneuver: McRoberts (hyperflex maternal hips)

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

Polyhydramnios: AFI >24 cm or DVP >8 cm

Delivery timing: A1GDM well-controlled to 40w6d; A2GDM well-controlled at 39w; poorly controlled earlier

Insulin needs drop precipitously at delivery (placental hormones gone)

Recurrence risk: 40–60% next pregnancy

Lifetime T2DM risk after GDM: ~50%

Breastfeeding benefit: halves maternal T2DM risk

GDM = sex-specific CVD risk enhancer per ACC/AHA

DPP trial: metformin or lifestyle reduces T2DM progression ~50% in prediabetes

Gestational DI: vasopressinase-mediated; treat with desmopressin (DDAVP), not vasopressin

Steroid hyperglycemia after betamethasone: lasts 3–5 days; anticipate insulin needs

WHO/ACOG screening week: 24–28 weeks; early if high-risk

Avoid OGTT post-bariatric surgery: dumping syndrome — use SMBG

Board Question Stem Patterns

— Stem: 32-year-old at first prenatal visit, BMI 33, prior 4.3 kg infant, A1c 5.9%

— Question: best next step?

— Answer: Early 50g GCT or 75g OGTT now, repeat at 24–28 weeks if negative

— Stem: 100g 3h OGTT — fasting 98, 1h 175, 2h 162, 3h 138

— Answer: GDM (fasting and 2h abnormal = ≥2 values)

— Stem: GDM patient with fasting 105, postprandial 130

— Answer: Bedtime NPH (target fasting hyperglycemia only)

— Stem: well-controlled A2GDM on insulin at 39 weeks

— Answer: Induce now (do not wait past 39w6d)

— Stem: GDM, EFW 4600 g at 38 weeks

— Answer: Offer scheduled C-section

— Stem: head delivered, turtle sign

— Answer: McRoberts maneuver first; never fundal pressure

— Stem: 6 weeks after delivery of GDM pregnancy

— Answer: 75g 2h OGTT

— Stem: first visit A1c 6.8%

— Answer: Overt diabetes in pregnancy; order fetal echo at 20–22 weeks

— Stem: A2GDM at 32 weeks needing betamethasone

— Answer: Anticipate hyperglycemia, intensify insulin/IV insulin × 3–5 days

— Stem: 3rd trimester polyuria, normal glucose, dilute urine, responds to DDAVP

— Answer: Gestational DI (vasopressinase), not GDM

— Stem: 2 years post-GDM, BMI 28, FPG 108

— Answer: Intensive lifestyle ± metformin (DPP)

Step 3 management: Recognize the A1 vs A2 classification language in stems — it determines fetal surveillance start, delivery timing, intrapartum insulin needs, and answer choices on multistep questions.

Pattern 1 — Early screening trigger:

Pattern 2 — Two abnormal values:

Pattern 3 — Insulin selection by pattern:

Pattern 4 — Delivery timing:

Pattern 5 — Macrosomia:

Pattern 6 — Shoulder dystocia:

Pattern 7 — Postpartum follow-up:

Pattern 8 — Overt vs gestational DM:

Pattern 9 — Steroid hyperglycemia:

Pattern 10 — Gestational DI mimicker:

Pattern 11 — Long-term prevention:

One-Line Recap

Gestational diabetes is glucose intolerance of pregnancy diagnosed at 24–28 weeks (earlier if high-risk), managed first with medical nutrition therapy and exercise then insulin if targets are unmet, with delivery timed by control status, mandatory 75g OGTT at 4–12 weeks postpartum, and lifelong T2DM/CVD surveillance.

Board pearl: Memorize three numbers and three timepoints — 95/180/155/140, 24–28 weeks, 39 weeks, 4–12 weeks postpartum — and most Step 3 GDM stems collapse to a single correct answer.

Screen all pregnant patients at 24–28 weeks (two-step GCT/OGTT preferred in US); screen early if BMI ≥25 plus a risk factor, prior GDM, or A1c ≥5.7%. Diagnose with ≥2 abnormal values on the 100g 3-hour OGTT (95/180/155/140) or any abnormal on the 75g 2-hour OGTT (92/180/153).

Treat with MNT + exercise first; targets are fasting <95, 1h pp <140, 2h pp <120. Add insulin (first-line) if ≥30% of values out of range over 1–2 weeks. Match insulin to glucose pattern — bedtime NPH for fasting elevations, prandial rapid-acting for postprandial elevations.

Deliver A1GDM by 40w6d, well-controlled A2GDM at 39w, poorly controlled earlier; offer scheduled cesarean if EFW ≥4500 g; stop all hypoglycemics at delivery; manage shoulder dystocia with McRoberts first.

Follow-up with 75g 2-hour OGTT at 4–12 weeks postpartum (non-negotiable Step 3 point), then lifelong T2DM screening every 1–3 years, breastfeeding encouragement, CVD risk reduction (GDM is a sex-specific risk enhancer), preconception counseling for future pregnancies, and a closed-loop OB-to-PCP handoff to prevent the most common transitions-of-care failure in this disease.