Are there risk factors for false-positive malformation diagnoses on obstetric ultrasound? A nested case-control study.

INTRODUCTION: In a population-based study, we found an overall false-positive rate of 8.8% for the second and third trimester ultrasounds. Although numerous studies have been performed to examine factors which lead to false negatives, the same is not true for the factors associated with false positives. The principal objective of this study was to look for risk factors for false-positive diagnoses of fetal malformations on obstetric ultrasound scans. MATERIAL AND METHODS: In this nested case-control study, the case infants were those whose mother had a false-positive antenatal ultrasound diagnosis of a malformation during the second or third trimester (ultrasound false-positives) and who were live - or stillborn in Auvergne in 2006-2010. The control group comprised all children who were ultrasound true-negatives in 2005 and 2007. The study included 46 cases and 184 controls, matched according to the level of the maternity unit in which they were born. RESULTS: Most false-positive diagnoses were minor malformations. The mean term at this false-positive diagnosis was 27.7±5.4 weeks; in 46.8% of cases, the diagnosis was made during the second-trimester ultrasound. A single malformation was suspected in 95.7% of the cases. In 97.9% of cases, only one anatomical system was affected. In all, 49 malformations were identified among the 46 cases and their distribution differed according to anatomical system. The only risk factor identified was a body mass index (BMI)<25 (ORa=1.7; 95%CI: 1.2-2.4). DISCUSSION: A maternal BMI<25 was the only risk factor identified for a false-positive ultrasound diagnosis of a fetal malformation.

Prenatal detection and outcome of congenital diaphragmatic hernia: a French registry-based study.

OBJECTIVES: To describe the true incidence, prenatal detection rate and fetal outcome of congenital diaphragmatic hernia (CDH) in a systematically registered population over an 18-year period and to determine any change in trends over time. METHODS: This was a retrospective study of all cases of CDH registered in the Central-Eastern France Birth Defects Registry from 1986 to 2003. All fetuses and infants up to 1 year of age diagnosed with CDH were registered, including miscarriages later than 22 weeks of gestation, stillbirths and terminations of pregnancy (TOP). Routine prenatal screening consisted of three ultrasound examinations and there was no upper limit of gestational age for TOP. RESULTS: Five hundred and one cases of CDH were identified from a total of 1 835 022 live births (2.7 cases per 10 000 live births). The overall prenatal detection rate was 54%. There was a significant increase over time in the detection rate mainly for associated CDH and left-sided CDH (P < 0.0001), and in the proportion of neonates delivered in tertiary centers (P < 0.0001). The overall survival rate at discharge was 47% and this increased significantly over time for isolated CDH (P = 0.04), whereas it was lower and remained stable for associated CDH (P = 0.64). The TOP rate for isolated CDH did not vary significantly in contrast to that for associated CDH cases in which the TOP rate increased over time, progressively replacing the neonatal death rate (P = 0.01). CONCLUSIONS: Over an 18-year period, this large population-based study demonstrated increasing prenatal detection rates for associated CDH and left-sided CDH and confirmed an increasing survival rate mainly for isolated CDH.