Aim: To establish the role of 1st trimester ultrasound in detecting fetal abnormalities by performing a 20-week ultrasound scan as a standard.

Study Design: A cross-sectional descriptive study.

Methods: A total of 380 cases were recruited from the Obstetrics and Gynecology department of Jinnah post graduate medical center Karachi for six months duration from January, 2021 to June, 2021. The patients were assessed at 11-14 weeks of pregnancy for the diagnosis of fetal anomalies in high-risk women taking 20 weeks gestation ultrasound scan as the gold standard.

Results: Out of 380 women, mean age was 27.47 ± 2.57 years. 238 (62.6%) women underwent ultrasound at 12 + 13 weeks and 142 (37.4%) women had it at the 10-11 weeks of amenorrhea. Regarding maternal risk factors, 46 (12.1%) women had advanced maternal age> 35 years, 21 (5.5%) women with a family history of chromosomal abnormalities, 4 (2.1%)  with a history of  Down syndrome in previous babies, 118 (30.8)%) women with a history of congenital abnormalities, 85 (21.6%) women with a previous pregnancy complicated by spontaneous abortion, 11 (3.4%) women with a previous child with cerebral palsy, 56 (14.2%) women with previous intrauterine death, 13 (3.4%) women with a history of thalassemia, 7 (1.8%) women with a history of multiple pregnancies and 22 (5.5%) women with associated medical complications; diabetes, hypertension. The sensitivity, specificity and predictive value of ultrasound in the diagnosis of fetal defects in high-risk women compared to the ultrasound at week 20 showed 91.9% sensitivity, 100% specificity, 100% positive predictive value and negative predictive value is 96.27%, and the diagnostic accuracy is 99.2%.

Conclusion: First trimester ultrasound is effective in detecting fetal anomalies.

Keywords: First trimester ultrasound, fetal anomaly, high-risk women