The value of first trimester ultrasound screening for fetal structural abnormalities

Objective: To explore the value of first trimester ultrasound screening (FTS) for fetal structural abnormalities. Method: This was a single-center retrospective study carried out at the Affiliated Suzhou Hospital of Nanjing Medical University. Total 7523 fetuses were enrolled in the study, including 6376 single pregnancies and 569 twin pregnancies, who underwent FTS during 11~13 +6 weeks’ gestation, including nuchal translucency (NT) measurement and anatomy scans with a standard protocol. The fetuses were followed-up with pregnancy outcomes. Results: : 147 fetuses (133 single pregnancies and 7 twin pregnancies) were lost to follow-up. A total of 119 fetuses with structural malformations were found by prenatal ultrasound, autopsy after induced abortion, or physical examination after birth, with a deformity incidence rate of 1.61% (119/7376). The highest defects were cardiac abnormalities (35/119, 29.4%), followed by genitourinary system abnormalities (14/119, 11.76%) and skeletal system abnormalities (13/119, 10.2%). Among 119 fetuses, 64 cases (64/119, 53.8%) with structural malformations were detected during the first trimester, while 24.4% (29/119) and 1.68% (2/119) were found during the second and third trimester, respectively. The other 24 cases with fetal structural malformation missed diagnosis prenatally. However, 4 cases with suspected ventricular septal defects (VSD) by FTS were proved to be normal. The sensitivity, specificity, positive predictive value (PPV), negative predictive value (NPV) for first trimester ultrasound was 54.2%, 99.9%, 94.1%, and 99.3%, respectively. On the other hand, 48 fetuses (48/452, 10.6%) with thickened NT (above the 95 th percentile) showed structural malformations. The prevalence of structural abnormalities was significantly higher in fetuses with increased NT (10.6%) than those with normal NT (71/6924, 1.0%) (P<0.01). Conclusion: FTS was a safe and useful approach for detecting fetal structural malformations early, with high specificity, PPV, and NPV. The increased NT could be a clue for detailed anatomy screening and much attention should be paid. However, it could not replace the second and third trimester ultrasound screening due to the mid-sensitivity.