Screening for Common Fetal Trisomies in Twin Pregnancies: First-Trimester Combined, Cell-Free DNA, or Both?

To examine the distribution of risks for fetal trisomies after first-trimester combined screening in twins and to investigate different strategies for clinical implementation of cell-free DNA (cfDNA) testing.

We retrospectively analyzed all twin pregnancies undergoing first-trimester combined screening over a 10 years' period. The population was stratified according to various risk cut-offs, and we examined different screening strategies for implementation of cfDNA testing in terms of impact on invasive testing rate, cfDNA test failure rate, and economic costs.

We included 572 twin pregnancies: 480 (83.92%) dichorionic and 92 (16.08%) monochorionic. Performing a first-line combined screening and offering cfDNA testing to the group with a risk between 1 in 10 and 1 in 1,000, would lead to an invasive testing rate of 2.45%, and cfDNA testing would be performed in 22.20% of the population. This strategy would be cost-neutral compared to universal combined screening alone.

First-trimester combined screening results can be used to stratify twin pregnancies into different risk categories and select those that could be offered cfDNA testing. A contingent screening strategy would substantially decrease the need for invasive testing in twins and it would be cost-neutral compared to combined testing alone.