Study finds low chromosomal abnormality rate in surviving co-twins after SSIUFD

Spontaneous single intrauterine fetal demise in twin pregnancies was associated with a low incidence of chromosomal abnormalities in surviving co-twins in a retrospective study of 88 pregnancies that underwent invasive prenatal testing between January 2015 and December 2024. Among the 24 cases tested for SSIUFD alone, no clinically significant chromosomal abnormalities were detected, and MCDA pregnancies showed significantly higher termination rates than DCDA pregnancies.

This retrospective study reviewed 88 twin pregnancies complicated by spontaneous SSIUFD that underwent invasive prenatal testing between January 2015 and December 2024. Cases of elective fetal reduction and those with unknown chorionicity were not included. The cohort included 54 dichorionic diamniotic (DCDA) and 34 monochorionic diamniotic (MCDA) pregnancies.

According to gestational age at the single twin demise, the pregnancies were classified into the first-trimester SSIUFD group at 12 weeks’ gestation or less and the second-trimester SSIUFD group at more than 12 weeks’ gestation. Genetic evaluation was performed using karyotyping and/or single nucleotide polymorphism (SNP) array analysis on samples of amniotic fluid in 85 cases and cord blood in three cases.

Of 88 cases, 24 (27.3%) underwent invasive prenatal diagnosis because of SSIUFD alone, while the remaining 64 (72.7%) had additional clinical indications. Among the 24 cases tested for SSIUFD alone, no clinically significant chromosomal abnormalities were detected (0/24, 0%). A low incidence of chromosomal abnormalities (1.1%, 1/88) was observed, with one case of trisomy 21 in a MCDA pregnancy, both twins exhibiting concordant ultrasound anomalies. SNP array analysis revealed no pathogenic submicroscopic variants in 68 analyzed cases.

Among 83 cases with follow-up information available, MCDA pregnancies showed significantly higher termination rates than DCDA (19.4% vs. 1.9%, p < 0.05), primarily due to severe anomalies or subsequent fetal demise followed SSIUFD. Overall, term deliveries occurred in 81.9% and preterm birth (PTB) in 9.6%, with comparable PTB rates (p > 0.05) between DCDA (13.5%) and MCDA (6.5%) groups, or between the first-trimester group (6.0%) and the second-trimester SSIUFD group (15.2%).

The findings did not provide evidence for an increased detection rate of chromosomal abnormalities in surviving co-twins after SSIUFD, particularly in surviving co-twins without other indications. Surviving co-twins from MCDA pregnancies were associated with a higher risk of adverse outcomes, including termination due to fetal malformations and subsequent fetal demise, highlighting the importance of close ultrasound monitoring in these cases.