| Summary: | Abstract Background In recent years, first-trimester intrauterine hematoma (IUH) has become increasingly common in twin pregnancy. The majority of studies on IUH have excluded twin pregnancies, and others did not differentiate between singleton and twin pregnancies. The impact of IUH on twin pregnancy is unclear. Therefore, the primary objective of our study was to examine associations between first-trimester IUH and pregnancy outcomes in twin pregnancies. Methods The data of 1020 twin pregnancies in women who received a routine examination from January 2014 to December 2018 were reviewed. We compared baseline data and pregnancy outcomes between those with and without IUH. Multivariable logistic regression analysis was used to adjust for possible confounding factors. Results A total of 209 patients (21.3%) developed IUH in the first trimester. First-trimester IUH was significantly associated with increased odds of miscarriage (adjusted odds ratio 14.27, 95% CI 8.25–24.70) and vanishing twin syndrome (adjusted odds ratio 3.26, 95% CI 1.11–4.61). However, there were no differences in the rates of stillbirth, preeclampsia, preterm labor (< 34 weeks), low birth weight, postpartum hemorrhage or fetal distress between the two groups. Maternal age, previous preterm birth, chorionicity in twins and the gestational week at first ultrasound did not differ between the two groups. The women with IUH had high rates of previous miscarriage (46.73% vs 38.37%, p = 0.01), assisted conception (48.56% vs 32.60%, p < 0.001) and accompanied vaginal bleeding (67.46% vs 13.43%, p < 0.001). According to the logistic regression analyses, these characteristics were not associated with pregnancy loss or vanishing twin syndrome. No IUH characteristics, including volume, largest diameter, or the presence of vaginal bleeding, were associated with pregnancy loss or vanishing twin syndrome before 20 weeks of gestation (P > 0.05). Conclusion In women with twin pregnancy, the presence of IUH in the first trimester was associated with the loss of one or both fetuses before 20 weeks of gestation. However, previous miscarriage, the conception method, the IUH size and the presence of vaginal bleeding were not independently associated with miscarriage or vanishing twin syndrome.
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