Pregnancy and Delivery Outcomes in Women With Persistent Versus Resolved Low-Lying Placenta in the Late Third Trimester

Trial of Labor Compared With Elective Cesarean Delivery for Low-Lying Placenta

OBJECTIVE

To compare outcomes of women with low-lying placenta by planned mode of delivery and distance from the internal os distance.

METHODS

Six tertiary maternity hospitals in France participated in this retrospective multicenter study of births from 2007-2012. Women with low-lying placenta , defined as an internal os distance of 20 mm or less, who gave birth after 35 weeks of gestation were included and classified in the planned trial-of-labor or elective cesarean delivery groups. The primary endpoint was severe postpartum hemorrhage (PPH) defined as blood loss exceeding 1,000 mL. Secondary outcomes were composite variables of severe maternal and neonatal morbidity. We used multivariable logistic regression and propensity scores to compare outcomes by planned mode of delivery.

RESULTS

Among 128,233 births during the study period, 171 (0.13%) women had low-lying placenta: 70 (40.9%) in the trial-of-labor group and 101 (59.1%) who underwent elective cesarean delivery. The rate of severe PPH was 22.9% (16/70, 95% CI 13.7-34.4) for the trial-of-labor group and 23.0% (23/101, 95% CI 15.2-32.5) for the cesarean delivery group ( P =.9); severe maternal and neonatal morbidity rates were likewise similar (2.9% vs 2.0% [ P =.7] and 12.9% vs 9.9% [ P =.5], respectively). Trial-of-labor was not significantly associated with a higher rate of severe PPH after multivariable logistic regression and propensity score-weighted analysis (adjusted odds ratio [aOR] 1.42, 95% CI 0.62-3.24 [ P =.4]; and aOR 1.34, 95% CI 0.53-3.38 [ P =.5], respectively). The vaginal delivery rate in the trial-of-labor group was 50.0% (19/38) in those with an internal os distance of 11-20 mm and 18.5% (5/27) in those with a distance of 1-10 mm.

CONCLUSION

Our results support a policy of offering a trial of labor to women with low-lying placenta after 35 weeks of gestation and an internal os distance of 11-20 mm. An internal os distance of 1-10 mm reduces the likelihood of vaginal birth considerably, compared with 11-20 mm, but without increasing the incidence of severe PPH or severe maternal morbidity.

Mode of birth in women with low-lying placenta: protocol for a prospective multicentre 1:3 matched case-control study in Italy (the MODEL-PLACENTA study)

INTRODUCTION

The term placenta praevia defines a placenta that lies over the internal os, whereas the term low-lying placenta identifies a placenta that is partially implanted in the lower uterine segment with the inferior placental edge located at 1-20 mm from the internal cervical os (internal-os-distance). The most appropriate mode of birth in women with low-lying placenta is still controversial, with the majority of them undergoing caesarean section. The current project aims to evaluate the rate of vaginal birth and caesarean section in labour due to bleeding by offering a trial of labour to all women with an internal-os-distance >5 mm as assessed by transvaginal sonography in the late third trimester.

METHODS AND ANALYSIS

The MODEL-PLACENTA is a prospective, multicentre, 1:3 matched case-control study involving 17 Maternity Units across Lombardy and Emilia-Romagna regions, Italy. The study includes women with a placenta located in the lower uterine segment at the second trimester scan. Women with a normally located placenta will be enrolled as controls. A sample size of 30 women with an internal-os-distance >5 mm at the late third trimester scan is needed at each participating Unit. Since the incidence of low-lying placenta decreases from 2% in the second trimester to 0.4% at the end of pregnancy, 150 women should be recruited at each centre at the second trimester scan. A vaginal birth rate ≥60% in women with an internal-os-distance >5 mm will be considered appropriate to start routinely admitting to labour these women.

ETHICS AND DISSEMINATION

Ethical approval for the study was given by the Brianza Ethics Committee (No 3157, 2019). Written informed consent will be obtained from study participants. Results will be disseminated by publication in peer-reviewed journals and presentation in international conferences.

TRIAL REGISTRATION NUMBER

NCT04827433 (pre-results stage).