The influence of discordant growth during pregnancy in dichorionic twins on adverse birth outcomes

To investigate the influence of growth discordance in different trimesters of dichorionic twins on frequent adverse birth outcomes (preterm birth (PTB), low birth weight (LBW), and small for gestational age (SGA)).

Based on the Hunan Maternal and Child Health Hospital (HMCH) twin pregnancy cohort. Participants with dichorionic twin pregnancies who received prenatal care and delivered at HMCH between January 2019 and December 2024 were divided into four groups: whole-pregnancy concordant group (n = 428), isolated third-trimester discordant group (n = 30), isolated first-trimester discordant group (n = 35), and whole-pregnancy discordant group (n = 12). Grouping was based on whether first- and third-trimester fetal growth measured by ultrasound is concordant and tracking adverse birth outcomes in each group.

Our study included 505 dichorionic twin pregnancies, with a maternal mean age of 30.97 ± 3.70 years. Compared to whole-pregnancy concordant group, isolated first-trimester discordant group did not have a higher risk of any adverse birth outcome (p ≥ 0.05), isolated third-trimester discordant group had a higher risk of SGA (RR = 3.48, 95 % CI: 2.38--5.10), and whole-pregnancy discordant group had a higher risk of both SGA and LBW (RR = 5.07, 95 % CI: 3.43-7.47; RR = 1.51, 95 % CI: 1.25-1.83). The risk of SGA and LBW was linearly correlated with the degree of growth discordance in the third trimester.

In dichorionic twin pregnancies, discordant growth in the first trimester does not increase the risk of adverse birth outcomes. The presence of discordant growth in the third trimester is the critical gestational period contributing to SGA and LBW. Therefore, it is essential to maintain growth concordance in dichorionic twins when entering the third trimester.