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)

Abstract

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).

Keywords: maternal medicine; prenatal diagnosis; ultrasonography.

Conflict of interest statement

Competing interests: None declared.

© Author(s) (or their employer(s)) 2021. Re-use permitted under CC BY-NC. No commercial re-use. See rights and permissions. Published by BMJ.

Figures

Figure 1

Flow chart: participants’ antenatal care and follow-up scans. *Trial of labour, the onset of labour could be spontaneous or induced through an artificial rupture of membranes, otherwise the woman should undergo a CS between 41 and 41+5 weeks. ** Trial of labour, a pharmacological induction of labour is allowed. ARM, artificial rupture of membranes; AS, abdominal scan; CS, caesarean section; FU, follow-up; IOL, induction of labour; IOD, internal os distance; TVS, transvaginal sonography; TOL, trial of labour; w: weeks.

Figure 2

TVS evaluation of low-lying placenta. cervical length of 2.17 cm (1); IOD of 1.28 cm (2); placental edge thickness of 0.681 cm (3) shown by the red arrow; the angle between the basal and chorionic plates is identified by the yellow dotted lines. IOD, internal os distance; TVS, transvaginal sonography.