Risk factors for abnormally invasive placenta: a systematic review and meta-analysis

<p><b>Purpose of the article.</b> To explore the strength of association between different maternal and pregnancy characteristics and the occurrence of abnormally invasive placenta (AIP).</p> <p><b>Materials and methods:</b> Pubmed, Embase, CINAHL databases were searched. The risk factors for AIP explored were: obesity, age >35 years, smoking before or during pregnancy, placenta previa, prior cesarean section (CS), placenta previa and prior CS, prior uterine surgery, abortion and uterine curettage, <i>in vitro</i> fertilization (IVF) pregnancy and interval between a previous CS, and a subsequent pregnancy. Random-effect head-to-head meta-analyses were used to analyze the data.</p> <p><b>Results:</b> Forty-six were included in the systematic review. Maternal obesity (Odd ratio, OR: 1.4, 95% CI 1.0–1.8), advanced maternal age (OR: 3.1, 95% CI 1.4–7.0) and parity (OR: 2.5, 95% CI 1.7–3.6), but not smoking were associated with a higher risk of AIP. The presence of placenta previa in women with at least a prior CS was associated with a higher risk of AIP compared to controls, with an OR of 12.0, 95% CI 1.6–88.0. Furthermore, the risk of AIP increased with the number of prior CS (OR of 2.6, 95% CI 1.6–4.4 and 5.4, 95% CI 1.7–17.4 for two and three prior CS respectively). Finally, IVF pregnancies were associated with a high risk of AIP, with an OR of 2.8 (95% CI 1.2–6.8).</p> <p><b>Conclusion:</b> A prior CS and placenta previa are among the strongest risk factors for the occurrence of AIP.</p>