Association Between Lateral Placenta and Adverse Maternal and Perinatal Outcomes: A Systematic Review and Meta‐Analysis

ABSTRACT Background Adverse maternal and perinatal outcomes such as preeclampsia, small‐for‐gestational age (SGA) and preterm birth remain major global health concerns. Beyond known high‐risk placental features, emerging evidence suggests lateral placenta to be associated with impaired uteroplacental blood flow resulting in placenta dysfunction and adverse outcomes. A better understanding of these associations requires synthesizing both crude and adjusted effect estimates from available evidence. Objectives To comprehensively review and synthesize available evidence on the association between lateral placenta and adverse maternal and perinatal outcomes. Search Strategy MEDLINE (PubMed), EMBASE, Scopus and Cochrane CENTRAL were searched on 25th August, 2025. Selection Criteria Studies that assessed the association between lateral placentation and adverse maternal and perinatal outcomes in singleton pregnancies. Data Collection and Analysis Data were independently extracted by two reviewers. The random‐effects model was used to pool estimates of both crude and adjusted odds ratios (ORs) with corresponding 95% confidence interval (CI). Statistical heterogeneity was assessed by the I 2 statistic and Cochran's Q test. Main Results Twenty one eligible studies with a total of 162 727 singleton pregnancies were included in the meta‐analyses. Lateral placenta was associated with preeclampsia (OR = 1.65, 95% CI: 1.25, 2.19, I 2  = 41.0%), SGA (OR = 1.40, 95% CI: 1.17, 1.68, I 2  = 69.0%), preterm birth < 34 weeks (OR = 2.10, 95% CI: 1.62, 2.72, I 2  = 0.0%), preterm birth < 37 weeks (OR = 1.50, 95% CI: 1.26, 1.80, I 2  = 60.5%), retained placenta (OR = 2.52, 95% CI: 1.60, 3.95, I 2  = 87.7%), and non‐vertex foetal presentation at birth (OR = 1.50, 95% CI: 1.19, 1.89, I 2  = 28.6%). Two individual studies reported independent association between lateral placenta and preeclampsia; with adjusted odds ratio (aOR) of 2.04 (95% CI: 1.28, 3.25) and 1.32 (95% CI: 1.04, 1.67). Pooled adjusted OR (95% CI) demonstrated increased odds of SGA (aOR = 1.84, 95% CI: 1.33, 2.53, I 2  = 0.0%), and retained placenta (aOR = 4.43, 95% CI: 1.70, 11.53, I 2  = 76.1%). Marginal increase in odds was noted for preterm birth < 34 weeks (aOR = 2.14, 95% CI: 1.34, 3.41, I 2  = 0.00%) and preterm birth < 37 weeks (aOR = 1.54, 95% CI: 1.11, 2.13, I 2  = 38.8%). Conclusions Lateral placenta is associated with increased odds of preeclampsia, SGA, preterm birth, non‐vertex foetal presentation, and retained placenta. After controlling for confounders, lateral placenta remained independently associated with increased odds of SGA, preterm birth, and retained placenta. More studies that adjust for confounders are, however, needed to further clarify and strengthen the evidence base of this independent association.