[Ultrasound screening and diagnosis of fetal structural abnormalities between 11-14 gestational weeks]

To assess the feasibility of ultrasound screening and diagnosis of structural fetal anomalies at the 11-14 week scan.

An observational prospective follow up study from March 2000 till May 2003 was performed at three referral centers by seven experienced sonographers with high-resolution ultrasound equipment. 1135 singleton pregnancies between 11+0 and 14+6 weeks gestation (w.g.) participated in the study. The first trimester scan included assessment of fetal number, viability and biometry, nuchal translucency [NT] measurement and fetal anatomy survey performed according to standardized published protocols. Increased NT > or = 95th centile and/or diagnosis of structural fetal anomaly was considered as indication for invasive prenatal diagnosis, early fetal echocardiogram and follow-up scans, including a detailed fetal anomaly scan at 18-22 w.g. and a third scan at 28-32 w.g. Pregnancy outcome was ascertained from hospital records, referring physicians or the patients themselves.

The overall prevalence of structural fetal anomalies in the present study was 4.6% (53/1135). 22% (12/53) of the structural anomalies were detected between 11-14 w.g. 9 of those had normal karyotype, and 3 were associated with chromosomal anomalies. Furthermore, 10 cases of increased NT, with or without non-immune hydrops fetalis, were associated with congenital heart disease, rare genetic syndromes and adverse pregnancy outcome later in gestation. The ultrasound detection rate of structural fetal anomalies in the present study increased from 22% (12/53), to 69% (37/53) and 79% (42/53) for the first trimester scan, the first and second trimester scans, and the combination of all three scans, respectively. 21% (11/53) of all structural fetal anomalies were missed by prenatal ultrasound.

The first trimester scan is a method of choice for the diagnosis of major structural fetal anomalies. NT measurement is a useful screening test for chromosomal anomalies. In cases with increased NT subsequent development of congenital heart disease, rare genetic syndromes or adverse pregnancy outcome should be ruled out. At present, the second trimester scan constitutes an indispensable tool for the detection of most structural abnormalities. Even in advanced gestation the prenatal diagnosis of certain anomalies is difficult and often unfeasible.