Association of a unicornuate uterus with adverse obstetric outcomes: A retrospective cohort study.

Objective To estimate the association of unicornuate uterus (UU) with adverse obstetric outcomes. Methods Using data from 26 737 singleton childbirths from a tertiary hospital from 1999 to 2019, we identified 44 births from women with a UU. A total of 367 births from women with a normal uterus were randomly selected as controls. The outcome measures were preterm birth (PTB), breech presentation, and cesarean delivery. The subdivisions of PTB and indications for cesarean delivery were described. Results The presence of UU was associated with an increased risk of PTB (adjusted risk ratio [aRR], 2.3; 95% confidence interval [CI], 1.1-4.9), breech presentation (aRR, 6.2; 95% CI, 2.9-13.2), and cesarean delivery (aRR, 2.1; 95% CI, 1.8-2.7). For women with a UU, most PTBs (7/9) were moderate to late PTBs, and approximately half of the PTBs (4/9) were iatrogenic due to preeclampsia (PE). Breech presentation, PE, and prior surgery for rudimentary horn resection were UU-related indications for cesarean delivery. Conclusions Women with a UU have a higher risk of PTB, breech presentation, and cesarean delivery. Understanding of the subdivisions of PTBs and indications for cesarean delivery might help clinicians when counseling women with pregnancy complicated by a UU.