Arcuate Uterus as an Independent Risk Factor for Adverse Pregnancy Outcomes.

Objective: The aim of the study is to estimate the association between arcuate uterus and pregnancy outcomes using controls selected from a similarly high-risk cohort.

Study Design: This is a retrospective cohort study of women with an arcuate uterus cared for by a single maternal-fetal medicine practice from 2005 to 2020. We included all women with a singleton pregnancy ≥20 weeks and diagnosis of arcuate uterus and randomly selected (3:1) patients with a singleton pregnancy and no uterine anomaly from the same practice as controls. Baseline characteristics and pregnancy outcomes were compared between the two groups. Chi-square, Fisher's exact, and independent samples -test were used for data analysis, as indicated.

Results: A total of 37 women with an arcuate uterus (55 independent singleton pregnancies) and 165 controls were included. There were no differences in baseline characteristics. Women with an arcuate uterus had a significantly higher rate of spontaneous preterm birth less than 37 weeks (10.9 vs. 3.0%,  = 0.031) and were more likely to require vaginal progesterone (5.5 vs. 0.6%,  = 0.049) and administration of antenatal corticosteroids (16.4 vs. 5.5%,  = 0.020). Arcuate uterus was also associated with lower birthweight (3,028.1 ± 528.0 vs. 3257.2 ± 579.9 g,  = 0.010) and higher incidence of intrauterine fetal growth restriction (20.0 vs. 7.3%,  = 0.008), despite similar starting body mass index (BMI) and weight gain throughout pregnancy. There were no differences in preeclampsia, malpresentation, cesarean delivery, blood transfusion, retained placenta, or morbidly adherent placenta.

Conclusion: Arcuate uterus is associated with a significantly increased risk of spontaneous preterm birth (<37 weeks), need for vaginal progesterone for short cervix and antenatal corticosteroids, fetal growth restriction, and lower mean birthweight. These findings suggest that arcuate uterus is not just a normal variant of uterine anatomy but rather a risk factor for poor fetal growth, short cervix, and a higher risk pregnancy.

Key Points: · Arcuate uterus is associated with increased risk of preterm birth and fetal growth restriction.. · Women with arcuate uteri had higher rates of vaginal progesterone use during pregnancy.. · Arcuate uterus should be treated as a true finding rather than a normal anatomical variant..