Severe First-Trimester Megacystis (>15 mm): A Case Report of Prognostic and Counseling Challenges Without Invasive Testing

First-trimester fetal megacystis is an uncommon but clinically significant finding on prenatal ultrasound because of its association with chromosomal anomalies and lower urinary tract obstruction. A 32-year-old gravida 2 para 1 woman presented for routine first-trimester evaluation at 12+6 weeks’ gestation. Sonography revealed a viable fetus with a crown-rump length of 64.3 mm and a fetal heart rate of 175 bpm. A grossly distended urinary bladder measuring 19.4 × 11.0 mm was noted. Nuchal translucency, nasal bone, and ductus venosus Doppler studies were normal. No keyhole sign or changes in renal echogenicity were observed. Amniotic fluid volume and placental morphology were consistent with gestational age. After thorough counseling about the risks of chromosomal abnormalities and progressive obstructive uropathy, the family refused invasive procedures and chose surgical termination. Histopathological evaluation was not performed. Severe first-trimester megacystis is strongly associated with adverse perinatal outcomes. This case highlights the prognostic uncertainty and counseling challenges encountered when invasive diagnostic confirmation is unavailable.