Publication:

Sequential first and second trimester ultrasound screening for early detection of fetal anomalies: a prospective observational study

Background First-trimester ultrasonography at 11–13⁺⁶ weeks plays a vital role in early detection of chromosomal abnormalities and structural fetal anomalies. When combined with a second-trimester anomaly scan at 18–24 weeks, it enhances diagnostic accuracy and improves pregnancy management.

Methods This prospective observational study was conducted at a tertiary care centre from January 2023 to January 2025 and included. The expected prevalence of fetal anomalies (3–5%) and, this sample size 220 randomly selected singleton antenatal women between 11–13⁺⁶ weeks of gestation was considered adequate to assess the detection rate with reasonable accuracy. First-trimester evaluation included nuchal translucency (NT), nasal bone, ductus venosus Doppler, tricuspid regurgitation, and early fetal anatomical survey. All participants subsequently underwent a detailed anomaly scan at 18–24 weeks.

Results This prospective observational study included 220 singleton antenatal women who underwent sequential ultrasound screening at 11–13⁺⁶ weeks and 18–24 weeks of gestation. A total of 11 foetuses (5%) were diagnosed with anomalies, of which 10 cases (4.55%) were detected during the first-trimester scan and 1 case (0.45%) during the second-trimester scan. Detected anomalies included chromosomal abnormalities (Trisomy 21,18, and 13), increased nuchal translucency, and structural defects involving the central nervous system, cardiac system, abdominal wall, and genitourinary system. Increased NT (>95th percentile) was observed in 6.4% cases. Anomalies were slightly more common in multigravida women and referred cases.

Conclusions In the present study, sequential first and second trimester ultrasound screening proved effective in early detection of fetal anomalies, enabling timely counselling and appropriate pregnancy management.