OBJECTIVE: To investigate the prevalence and national prenatal detection rate (DR) of major CHD (mCHD) in twin pregnancies without twin-to-twin transfusion syndrome (TTTS)-associated CHD in a population following a universal, standardized prenatal screening program.

METHODS: All Danish twin pregnancies are offered standardized screening and surveillance programs besides the 1st and 2nd -trimester screening for aneuploidies and malformation, respectively: Monochorionic twins every two weeks from gestational week 15, and dichorionic twins every four weeks from week 18. The study was performed retrospectively with prospectively collected data. The data were retrieved from the Danish Fetal Medicine Database and included all twin pregnancies from 2009-2018, where at least one fetus had a mCHD diagnosis pre- and/or postnatally. A mCHD was defined as a CHD requiring surgery within the first year of life, excluding ventricular septal defects. All pregnancies were pre- and postnatally validated in the local patient files at the four tertiary centers covering the entire country.

RESULTS: A total of 60 cases from 59 pregnancies were included. The prevalence of mCHD in twins was 4.6 per 1,000 twin pregnancies (95% confidence interval (CI) 3.5-6.0) (1.9 per 1,000 liveborn children (95% CI 1.3-2.5)). The prevalence for DC and MC were 3.6 (95% CI 2.6-5.0) and 9.2 (95% CI 5.8-13.7) per 1,000 pregnancies, respectively. The national DR of mCHD in twin pregnancies for the entire period was 68.3%. The highest detections were in cases with univentricular hearts (100%) and the lowest with a total anomaly of the pulmonary venous return, Ebstein's anomaly, aortic valve stenosis, and coarctation of the aorta (0-25%). Mothers of children with undetected mCHD had a significantly higher BMI compared to mothers of children with a detected mCHD (median 27 and 23, respectively, p=0.03).

CONCLUSIONS: The prevalence of mCHD in twins was 4.6 per 1,000 pregnancies, and more frequent in MC twins. Moreover, the DR of mCHD in twin pregnancies was 68.3%. A higher maternal BMI was more frequent in cases of undetected mCHD. This article is protected by copyright. All rights reserved.