Amniocentesis in twin gestation: the association between gestational age at procedure and complications.

Third trimester amniocentesis is often performed when indications arise after 24 weeks of gestation—typically to investigate new sonographic findings, and might be related to pre-term birth. Scarcity of data exists concerning the risks of third-trimester amniocentesis in twin pregnancies. A retrospective cohort study of all twin gestations that underwent amniocentesis in a tertiary hospital between 2007 and 2016. Outcomes and procedure-related complications were compared between third-trimester (≥ 24 weeks) and mid-trimester amniocentesis (16–23 weeks). Primary outcome was defined as membrane rupture within four weeks of procedure. Logistic regression analysis was utilized to adjust results to potential confounders. Overall, 185 eligible women were included, of them, 28 (15.1%) underwent third-trimester amniocentesis and 157 (84.9%) underwent mid-trimester amniocentesis. Women in the third-trimester amniocentesis group were younger and presented higher frequencies of intra-uterine growth restriction (31.5 vs. 35.3, p < 0.001, and 28% vs. 10% p = 0.015, respectively). The prevalence of membrane rupture within 4 weeks of the procedure was significantly higher in the third-trimester amniocentesis group (31% vs. 1%, p < 0.001). Delivery rates after third-trimester amniocentesis within 1, 2 and 4 weeks of the procedure were 11%, 14.8% and 52%, respectively, versus 0% following mid-trimester amniocentesis (p < 0.001). Gestational age at delivery was similar between the groups (35.7 vs. 36.4 gestational weeks, p = 0.34). In multivariate analysis, gestational age at amniocentesis was found to be an independent risk factor for premature rupture of membranes within 4 weeks of the procedure. Third trimester amniocentesis in twin pregnancies is associated with significantly higher rates of procedure-related membrane rupture compared to mid-trimester amniocentesis.