Detection of fetal structural abnormalities by an 11-14-week ultrasound dating scan in an unselected Swedish population.

BACKGROUND: To determine the detection rate of fetal structural abnormalities by a routine 11-14-week ultrasound scan for dating in an unselected pregnant population.

METHODS: A prospective observational cohort study of 2,708 unselected pregnant women attending an abdominal ultrasound examination at 11-14 weeks gestation. The number of major fetal structural abnormalities diagnosed after birth was obtained from a computerized database at the same unit.

RESULTS: Out of 2,708 pregnant women, 89 (3.3%) were found to have a missed abortion at the time of the ultrasound scan and 33 (1.2%) were diagnosed as twins. Thirteen major structural abnormalities were detected, three cases of anencephaly (one case also had a spina bifida), one case with hydranencephaly, one fetus with Dandy-Walker syndrome, two cases with gastroschisis, one case with a bilateral hydronephrosis, one case with a generalized hydrops, one fetus with multiple malformations, and three cystic hygromas. An additional 19 major structural defects were detected at birth. Four cases of neural tube defects and nine fetuses with congenital heart defects were diagnosed. The antenatal ultrasound detection rate was 40.6% (13/32). Nine patients had a nuchal translucency greater than 3.0 mm (excluding cystic hygromas); two of them had chromosomal abnormalities (trisomy 21 and trisomy 18).

CONCLUSIONS: Fetal structural abnormalities were detected in 41% (95%CI = 24-59) of the cases in an unselected pregnant population at a routine 11-14-week ultrasound scan for dating purpose. Two out of nine fetuses with a nuchal translucency greater than 3.0 mm had a chromosomal abnormality.