To analyze the relationship between nuchal translucency (NT) thickening and adverse pregnancy outcomes in twins during the first trimester.

Five hundred and three twin pregnancies were selected from those who underwent first trimester ultrasound screening during May 2017 to August 2019 at the Affiliated Suzhou Hospital of Nanjing Medical University, including 367 cases of dichorionic diamniotic (DCDA) twin pregnancy, 132 cases of monochoric diamniotic (MCDA) twin pregnancy, and 4 cases of monochoric monoamniotic (MCMA) twin pregnancy. The fetal crown-rump length (CRL) and NT thickness were measured according to the guidelines of the Fetal Medicine Foundation (FMF) and the pregnancy outcomes were followed. The pregnancy outcomes of twin pregnancy were compared between the group with normal fetal NT thickness in both fetuses and the group with NT thickening in at least one fetus. The latter group was further divided into a DCDA subgroup and an MCDA subgroup, and the former group was further divided into an NT ≥ 95th percentile subgroup and an NT ≥ 99th percentile subgroup. Differences in pregnancy outcomes between the above groups or subgroups were compared using the χ² test or Fisher exact probability method.

The average NT thickness of 1006 fetuses from 503 twin pregnancies was (1.83±0.56) mm (range, 0.8~10.0 mm). Four hundred and fifty-five cases (455/503, 90.46%) had normal fetal NT thickness in both fetuses, of which 57 (57/455, 12.52%) had abnormal pregnancy outcomes. Forty-eight cases (48/503, 9.54%) had NT thickening in at least one fetus, of which 15 (15/48, 31.25%) had abnormal pregnancy outcomes. The incidence of adverse pregnancy outcomes in twin pregnancy with NT thickening in at least one fetus was significantly higher than that with normal NT thickness in both fetuses (χ²=12.409, P＜0.001). There were 4 cases (4/48, 8.33%) of abortion or stillbirth when NT was thickened in at least one fetus, and 12 cases (12/455, 2.64%) of abortion or stillbirth occurred when the NT thickness of both fetuses was normal; the difference was statistically significant (χ²=4.574, P=0.032). There were 37 (37/48, 77.08%) cases in the DCDA subgroup, of which 8 (8/37, 21.62%) had adverse pregnancy outcomes. There were 11 (11/48, 22.92%) cases in the MCDA subgroup, of which 7 (7/11, 63.63%) had adverse pregnancy outcomes. The difference in the cases with adverse pregnancy outcomes was statistically significant between the two subgroups (χ²=6.967, P=0.008). There were 35 cases in the NT≥95th percentile subgroup, of which 10 (10/35, 28.57%) had adverse pregnancy outcomes, and 13 cases in the NT≥99th percentile subgroup, of which 5 (5/13, 38.46%) had adverse pregnancy outcomes; there was no significant difference in cases with adverse pregnancy outcomes between the two subgroups (χ²=0.432,P=0.511). One (1/35, 2.86%) case of termination of pregnancy occurred in the NT≥95th percentile subgroup, but there were 4 (4/13, 30.77%) cases in the NT≥99th percentile subgroup; there was a significant difference between the two groups (χ²=7.914,P=0.005).

NT thickness is an important ultrasonic soft marker during the first trimester. In twin pregnancy, especially in MCDA, NT thickening during the first trimester screening may indicate adverse pregnancy outcomes.