# The Pre-Twin Screen Consortium proposal for fetal structural anomalies evaluation across all three trimesters in twin pregnancies

## TL;DR

This study evaluates fetal structural anomalies in twin pregnancies across all three trimesters to improve prenatal diagnosis and management.

## Contribution

The study introduces a structured approach for evaluating fetal anomalies in twin pregnancies using detailed scans in all trimesters.

## Key findings

- Anomalies were detected in 4.1% of fetuses, with most identified in the first and second trimesters.
- Detailed scans in all trimesters improved diagnosis, genetic counseling, and delivery planning for twin pregnancies.

## Abstract

In singleton pregnancies, routine ultrasound examinations in each trimester improves the diagnosis of fetal abnormalities and their management. In this study, we examine twin pregnancies and report on the detection of fetal anomalies in each trimester and postnatally as well as on the type of anomalies and their prevalence.

This prospective multicenter study enrolled pregnant women with dichorionic (DC) and monochorionic diamniotic (MCDA) twins at gestational weeks (GA) 11 + 0 to 13 + 6 in six medical centers (two in Germany, and one each in Spain, Canada, Italy, and Israel). Pregnancies were dated by the crown-rump length of the larger twin. Detailed scans were performed according to the guidelines of the International Society of Ultrasound in Obstetrics and Gynecology (ISUOG) at enrollment at gestational week (GA) 11 + 0 to 13 + 6, and at GA 20 + 0 to 22 + 6 and GA 28 + 0 to 32 + 6. Neonatal examinations were conducted in each case. Malformations were confirmed after delivery or postmortem in cases of fetal death or termination of pregnancy (TOP).

Of the 649 twin pregnancies (1298 live fetuses) at enrollment, there were 436 (70.6%) DC and 182 (29.4%) MCDA pregnancies. In total, 1168 babies were liveborn to 618 mothers (808 DC and 360 MCDA twins) after excluding cases lost to follow-up and TOPs. Anomalies were identified in 4.1% of the fetuses (48/1168). Of the 48 fetuses with anomalies, 17 (35.4%) were identified in the first, 21 (43.8%) in the second, and 6 (12.5%) in the third trimester. Additional 4 (8.3%) were identified postnatally. Of the anomalies, 37 were in fetuses from DC twins (4.57%), and 11 (3.05%) in MCDA twins.

We demonstrate the utility of detailed fetal scans in twin pregnancies in all three trimesters. First- and second-trimester diagnosis enables genetic counseling and testing, and informed parental decisions of pregnancy management. In addition to alerting the parents to the presence of fetal anomalies, third-trimester scans enhanced delivery planning and newborn care.

The online version contains supplementary material available at 10.1007/s00404-025-08044-0.