Sensitivity of obstetrical ultrasonography in the prenatal diagnosis of major fetal anomalies

With the aim of evaluating the sensitivity of obstetrical ultrasonography for prenatal screening of major birth defects, a retrospective study was conducted on 164 pregnancies which ended in the birth of an affected baby. The 164 cases had been reported to the Birth Defects Monitoring System of the Bouches du Rhône area by 5 maternity Hospitals between January 1, 1985 and December 31, 1987. Among these 164 cases, 50 were live births, 19 died after birth, 21 were stillbirths and 74 were terminations of pregnancy after prenatal diagnosis. Data from ultrasound reports were cross-checked with data from clinical examination at birth for live births, or from systematic protocol applied to every stillbirth or termination of pregnancy. The 164 notified cases had 196 major fetal anomalies. The results showed that the overall sensitivity of ultrasonography for detection of major fetal anomalies was 75%. The detection rate was assessed for each anomaly. The advised timing for morphological examination of the fetus by ultrasound in France is 20-22 and 30-32 weeks' gestation. Among the major fetal anomalies which were ultimately detected in utero, only 28% were screened before 22 or by 22 weeks' gestation and 14% were not by 32 weeks' gestation. This study underlines the effectiveness of this technique in prenatal diagnosis of major birth defects but also its limits, mainly linked to the lateness of many diagnoses.