Relationship between Abnormal Placenta and Obstetric Outcomes: A Meta-Analysis

Abstract

The placenta has several crucial physiological functions that help maintain a normal pregnancy. Although approximately 2-4% of pregnancies are complicated by abnormal placentas, obstetric outcomes remain understudied. This study aimed to determine the outcomes and prevalence of patients with abnormal placentas by conducting a systematic review of 48 studies published between 1974 and 2022. The cumulative prevalence of circumvallate placenta, succenturiate placenta, multilobed placenta, and placenta membranacea were 1.2%, 1.0%, 0.2%, and 0.004%, respectively. Pregnancies with a circumvallate placenta were associated with an increased rate of emergent cesarean delivery, preterm birth (PTB), and placental abruption compared to those without a circumvallate placenta. The succenturiate lobe of the placenta was associated with a higher rate of emergent cesarean delivery, whereas comparative results were observed in terms of PTB, placental abruption, and placenta previa in comparison to those without a succenturiate lobe of the placenta. A comparator study that examined the outcomes of multilobed placentas found that this data is usually unavailable. Patient-level analysis (n = 15) showed high-rates of abortion (40%), placenta accreta spectrum (40%), and a low term delivery rate (13.3%) in women with placenta membranacea. Although the current evidence is insufficient to draw a robust conclusion, abnormal placentas should be recognized as a high-risk factor for adverse outcomes during pregnancy.

Keywords: abnormal placenta; bilobed placenta; circumvallate placenta; multilobed placenta; placenta membranacea; succenturiate lobe; systematic review.

Figure 1

Study selection scheme of the current systematic review.

Figure 2

Meta-analysis of the effect of a circumvallate placenta on obstetric outcomes. The figure shows pooled ORs for (A) PTB (unadjusted) [11,12,26,62], (B) FGR (unadjusted) [11,12,26,62], and (C) placental abruption (unadjusted) [11,12,26] between women with and without at circumvallate placenta. Forest plots were ordered within the stratum by year of publication and relative weight (%) of the study. The size of colored boxes represents the weight of study and position is a point of the estimated odds ratio. Heterogeneity was considerable in the analysis of PTB and FGR ((A): I² = 89%, (B): I² = 81%), while there was none in the analysis of placental abruption ((C): I² = 0%). Some values listed in the Figure may be slightly different from the original values since the calculations were done using RevMan ver. 5.4.1. Abbreviations: OR, odds ratio; CI, confidence interval; SE, standard error; PTB, preterm birth; FGR, fetal growth restriction.

Figure 3

Meta-analysis of the effect of a circumvallate placenta on rate of cesarean delivery. The pooled odds ratios (ORs) for (A) cesarean delivery (unadjusted) [11,12,26], (B) elective cesarean delivery (unadjusted) [11,12], and (C) emergent cesarean delivery (unadjusted) [11,12] between women with and without a circumvallate placenta are shown. Forest plots were ordered within the stratum by year of publication and relative weight (%) of the study. The size of colored boxes represents the weight of study and position is a point of the estimated odds ratio. Considerable heterogeneity was observed in the analysis of cesarean delivery and emergent cesarean delivery ((A): I² = 91%, (C): I² = 88%), while the analysis of elective caesarian delivery showed moderate heterogeneity ((B): I² = 47%). Some values in the Figure may be slightly different from the original values since the calculations were done using RevMan ver. 5.4.1. Abbreviations: CD, cesarean delivery; CI, confidence interval; SE, standard error.