Location, Location: Reassessment of Placental Location and Obstetric Risks

BACKGROUND Anterior placental location has been cited as an independent risk factor for adverse obstetric outcomes, including need for induction of labor, postpartum hemorrhage (PPH), retained placenta, intrapartum Cesarean delivery, and pre-eclampsia diagnosis. (1-4) However, robust evidence to support this association is limited. OBJECTIVE To evaluate the relationship between placental location and subsequent maternal and neonatal outcomes. STUDY DESIGN We conducted a retrospective cohort study of patients who delivered at the Mayo Clinic (Rochester, MN) between May 2018 and May 2023. Patients with singleton pregnancies and ultrasound-confirmed placental location between 16-22 weeks were included. Patients with low-lying placenta, placenta previa, abnormal placentation, uterine anomalies or scheduled Cesarean delivery were excluded. Placental location was categorized as anterior, posterior, lateral, or fundal. Maternal outcomes included postpartum hemorrhage (PPH), prelabor rupture of membranes (PROM), mode of delivery, induction of labor, third-stage duration, and diagnosis of a hypertensive disorder of pregnancy or gestational diabetes. Neonatal outcomes included Apgar scores, birth weight, small for gestational age (SGA), large for gestational age (LGA), and NICU admission. Continuous variables were compared by one-way ANOVA; categorical variables by χ² or Fisher’s exact test. Bonferroni correction was applied for multiple comparisons. RESULTS A total of 4,145 patients were included (placental location: anterior n=2,039; posterior n=1,866; lateral = 158; fundal = 82). Demographic characteristics did not differ significantly across groups. The only maternal outcome achieving statistical significance after Bonferroni correction was PROM [including term or preterm rupture of membranes] (p=0.0003): rates were highest in fundal (18.3%) and lateral (11.4%) groups compared to anterior (7.3%) and posterior (6.8%) placentas. Rates of PPH, induction of labor, delivery modality, third-stage duration, and hypertensive disorders of pregnancy did not differ according to placental location. No neonatal outcomes met the Bonferroni-corrected significance threshold, though a trend toward higher rates of SGA neonates was noted in the lateral group (11.4% vs 5.9% posterior, overall unadjusted p=0.024). CONCLUSIONS Contrary to prevailing clinical assumptions, anterior placentation was not associated with increased rates of PPH, labor induction, or operative delivery in this cohort. Fundal placental location was associated with higher rates of PROM. These findings suggest clinical counselling about placenta-related obstetric risk may need to be reassessed, with particular attention to fundal placental location and PROM risk.