Prenatal diagnosis of structural malformations and chromosome anomalies Detection, influence of Body Mass Index and ways to improve screening

Sammanfattning: Introduction: Prenatal diagnosis of structural malformations and chromosome anomalies is possible in the presence of an effective screening with ultrasound during pregnancy. The continuous evolution of the ultrasound equipment facilitates the examination. However there are challenges in terms of the increasing prevalence of obesity among the pregnant women and the need of training of the personnel performing the scans. In the Southeast region of Sweden all pregnant women are offered screening with ultrasound during pregnancy. From 2009 almost all women in the region are offered two examinations, one in week 11-14 assessment of gestational age and combined screening for aneuploidy. Congenital heart disease (CHD) is the most common congenital defect. About one third of the CHD cases will have a duct-dependent anomaly that is potentially life-threatening if not detected before birth.Aims: To assess the sensitivity for detecting structural malformations and chromosome anomalies by a routine ultrasound either in gestational week 11-14 or 18-20. To estimate the influence of a high Body Mass Index (BMI) in detecting fetal structural anomalies by ultrasound. To evaluate the possibility for introducing a more accurate fetal cardiac ultrasound screening based on five different transverse views and color Doppler. To determine if the risk-estimate for trisomy 21 from the screening procedure varies over BMI strata and if obesity is associated with an increased risk of Down syndrome in the offspring.Material and methods: Outcome measures from 21189 consecutive ultrasound examinations in the first and second trimester were analyzed and compared. The fetal anomaly diagnoses were also grouped in four BMI-groups. Then, a two-day course in examining of the fetal heart was given, analyzed and followed up. To evaluate the effect of BMI on the combined screening, 10224 patients were divided in six BMI categories. Outcomes were evaluated over BMI strata. The possibility of an association between maternal obesity and Down syndrome was analyzed in a nationwide cohort of 1568604 women giving birth in Sweden.Results: At the first trimester scan 13% of all anomalies were detected vs 29% in the second trimester. For aneuploidy the corresponding results were 71% vs 42%, and for lethal anomalies 88% vs 92%. If divided into BMI-groups 26% of the malformations were detected in the group of normal weight women compared to 19% among the obese. For malformations with long-term handicap the corresponding figures were 46% vs 27%. After the course in examination of the fetal heart uncertainty was lower and the familiarity with the new technique was enhanced. The ability to perform the new method remained at follow up. In the combined screening, the observed and expected number with a risk of Downs syndrome >1/300 were similar in each BMI-group. Obese women had an increased risk of giving birth to an infant with Downs syndrome compared with normal weight women.Conclusions: There was an advantage to the scan in the second trimester discovering malformations overall and an advantage to the early scan concerning aneuploidy. Lethal malformations were detected at a high level in both groups. The detection rate seemed lower for the obese women. In the screening for Down syndrome, the risk-estimate is unaffected by BMI. Detection of heart malformations needs improvement. By implementing new image modalities and providing hands-on training uncertainty in examining the fetal heart can be reduced.