First-trimester screening and small for gestational age in twin pregnancies: a single center cohort study.

Objective : This study aimed to investigate the association between maternal factors and first-trimester biophysical and biochemical markers with small for gestational age (SGA) neonates in twin pregnancies (TwPs). Methods : Single center retrospective cohort study of TwPs followed from January 2010 to December 2022 at a tertiary perinatal center, Lisbon, Portugal. Inclusion criteria consisted of 572 TwPs. Maternal and pregnancy characteristics, mean arterial pressure, pregnancy-associated plasma protein-A (PAPP-A), β-human chorionic gonadotropin (β-HCG), and uterine artery pulsatility index (UtA-PI) were analyzed. Univariable, multivariable logistic regression (LR) and receiver-operating characteristic curve analyses were performed. The main outcomes measures considered were: SGA <3 ^rd , <5 ^th and <10 ^th percentile, composite outcome of SGA concurrent with preterm birth (PTB) (<32, <34, and <36 weeks). Results : TwPs affected with SGA <3 ^rd , <5 ^th or <10 ^th percentiles were 120/572 (20.9%), 157/572 (27.4%) and 190/572 (33.2%), respectively. SGA <3 ^rd percentile was associated with higher rate of PTB, 59.0% of cases <32 weeks, OR 6.4 (95%CI: 3.2-12.7, p<0.001). UtA-PI and PAPP-A were identified as significant independent risk factors associated with SGA, as well as with the composite outcome of SGA concurrent with PTB. A LR model was obtained for the composite outcome SGA <3 ^rd percentile and PTB <32 weeks, with an AUC of 0.765, a sensitivity rate of 70%, and a false positive rate of 20%. Conclusion: SGA concurrent with prematurity significantly impacts TwPs, and the majority of pregnancies at risk for this outcome can be detected in the first trimester. However, larger datasets are necessary to develop robust predictive models. Synopsis: The association between first-trimester screening data and SGA concurrent with very preterm birth in twin pregnancies was determined in most of the cases.