Comparisons of first and second trimester screening for fetal anomalies.

Four thousand fifty unselected pregnant women bearing a total of 4,078 fetuses were examined by transvaginal sonography (TVS) at 14 weeks of gestational age and rescreened via transabdominal sonography (TAS) at 21 weeks. Fifty-four of 88 anomalies were correctly identified at first scan whereas 34 were not; of these, 24 were discovered at second trimester rescreening, and the remaining 10 were observed later in pregnancy or after birth. The sensitivity of TVS screening with respect to final outcome was 61.4% (54 of 88 malformations in total) and 69.2% in comparison to TAS screening results (54 malformations detected among 78 recognized within 21 weeks). The association between fetal malformation and chromosomal aberrations was also investigated: in our study population there were 21 aneuploidies, 14 of which were recognized because of abnormal findings at the 14 weeks' TVS, 5 at the TAS rescreening, and 2 after birth in neonates free of structural abnormalities.