Large-for-Dates Baby Bump: Causes, Evaluation & When to Worry

Common Causes of Increased Fundal Height / Abdominal Circumference

1. Multiple Gestation: Twins/triplets → uterus larger than singleton dates.
2. Polyhydramnios: Excess amniotic fluid (AFI >24 cm or DVP >8 cm). Causes: fetal anomalies (GI/neural tube), maternal diabetes, fetal anemia, infections, idiopathic (~60%). ACOG: 1–2% of pregnancies.
3. Large for Gestational Age (LGA) Fetus: Estimated fetal weight >90th %ile. Causes: genetics, maternal obesity, gestational diabetes, post-term.
4. Uterine Masses: Fibroids (leiomyomas), ovarian cysts, placental abnormalities (placenta percreta).
5. Measurement Variability: Inconsistent technique (bladder fullness, tape placement, examiner).
6. Abdominal Distension: Gas, constipation, bloating – mimics uterine size.
7. Incorrect Dating: LMP uncertainty, irregular cycles → gestational age overestimation.

Clinical Evaluation

• Confirm dates with early ultrasound (crown-rump length).
• Serial fundal height measurements (same examiner, empty bladder).
• Ultrasound for AFI, EFW, fetal anatomy, placental location, fibroids.
• Glucose tolerance test if not done.
• Maternal serum screening / NIPT if aneuploidy concern.

Red Flags (Prompt Evaluation)

• Sudden increase in fundal height (>3 cm/week or >90th %ile jump).
• Symptoms: dyspnea, uterine tenderness, decreased fetal movement, preterm contractions.
• Known diabetes, prior LGA, multiple gestation.

Most causes are benign or manageable; timely assessment ensures appropriate monitoring.