Subchorionic hematoma and risk of preterm delivery: a systematic review and meta-analysis

This study aimed to investigate the association between early pregnancy with subchorionic hematoma and preterm delivery and other adverse pregnancy outcomes in singleton pregnancies.English studies published from 2000 to July 15, 2022 were retrieved from PubMed, Web of Science, and the Cochrane Library.The inclusion criteria were: singleton pregnancy, subchorionic hematoma, and perinatal outcomes. Studies including multiple pregnancy, basic molecular studies, case reports (series), and conference reviews were excluded.Data analysis was mainly conducted with Review Manager (RevMan) and Stata, and the results were represented with odds ratios and 95% confidence intervals. The methodological quality of the included studies was evaluated by the Cochrane risk assessment scale.In total, 370 studies were retrieved from the above databases. Our review included 16 studies and divided them into 2 subgroups: natural pregnancy (12 studies) and assisted reproductive pregnancy (4 studies). The relevant characteristics of each study were analyzed in detail. The primary outcome was preterm delivery. The secondary outcomes were miscarriage, fetal growth restriction, cesarean delivery, and preeclampsia. We found that subchorionic hematoma in the first trimester was not significantly associated with preterm delivery (odds ratio, 1.11; 95% confidence interval, 0.82-1.51) or other adverse outcomes in singleton pregnancy. Regression analysis found that the large heterogeneity of the included studies might be related to whether the included study population (early pregnancy with subchorionic hematoma) was complicated with threatened abortion (P<.05). However, no studies caused large heterogeneity according to sensitivity analysis. Finally, 15 studies related to preterm delivery did not have publication bias (Egger test: P=.26). However, subchorionic hematoma in the first trimester was associated with miscarriage in single pregnancies (natural pregnancy: odds ratio, 3.07; 95% confidence interval, 1.98-4.75; assisted reproductive pregnancy: odds ratio, 1.45; 95% confidence interval, 1.1-1.90).In singleton pregnancy, we found no association between subchorionic hematoma in the first trimester and preterm delivery. Although there was a correlation with miscarriage, the possible gestational age of miscarriage was not stated. More studies are needed to further address the herein posed research questions.