911: Fetal growth restriction in smaller twin of monochorionic diamniotic pair with discordant estimated fetal weights

Abstract

To identify predictors of selective fetal growth restriction (sFGR) in the smaller twin of a monochorionic diamniotic (MCDA) pair complicated by estimated fetal weight discordance (EFWD) of at least 20%. This was a retrospective cohort study of all MCDA twin pregnancies evaluated at a single institution from 2008 to 2018. Inclusion criteria were EFWD ≥ 20% before 27 weeks and adequate ultrasound (US) information to assess for interval growth until delivery, defined as last US within 5 weeks of delivery. We excluded those with major structural anomalies, pregnancies that were terminated, those that developed twin-twin transfusion syndrome, and those that developed polyhydramnios. The primary outcome was development of sFGR in the smaller twin, defined as estimated fetal weight ≤ 10th percentile for gestational age (GA). Predictors included maternal demographics (age, nulliparity, and use of assisted reproductive technology), US findings (cord insertion of smaller twin and presence of arterio-arterial anastomosis), and details at time of EFWD diagnosis (GA at diagnosis and degree of EFWD). The Kruskal-Wallis test generated median values for non-parametric continuous variables, and Fisher’s exact tests compared proportions between categorical variables. A total of 38 MCDA pairs met the inclusion criteria, with 26 (68%) developing sFGR at a median GA of 23.9 weeks (20.7-35.1). There were no statistically significant differences in maternal demographics, US findings, or GA at time of EFWD diagnosis comparing those who developed sFGR and those who did not. The sFGR group had a greater degree of EFWD at initial diagnosis, which approached but did not reach statistical significance (median EFWD 32.8% vs 29.2%, p = 0.055). The relative risk of developing sFGR with initial EFWD ≥ 30% was 1.3 (95% CI 0.8-2.1). The majority of MCDA twins with EFWD ≥ 20% ultimately develop sFGR in the smaller twin. While a statistically significant difference was not reached, we did observe a trend toward a greater degree of EFWD being associated with subsequent development of sFGR. Larger studies are required to further evaluate this finding and to enable providers to risk-stratify MCDA pairs with EFWD.