: To evaluate the association between endometriosis and the risk of preeclampsia and other maternal outcomes in spontaneously conceived women.

: PubMed, MEDLINE, EMBASE, Scopus, Cochrane Library, Web of Science, and Google Scholar were systemically searched for studies published from inception until November 2021 (CRD42020198741). Observational studies published in English or French that investigated the risk of preeclampsia in women with endometriosis who conceived spontaneously were included.

: 610 articles were reviewed once duplicates were removed. Inclusion criteria included spontaneous conception and surgical and/or imaging ascertainment of an endometriosis diagnosis. Exclusion criteria included conception using assisted reproductive technologies (ART), multiple pregnancies, chronic hypertension, and unclear diagnoses of endometriosis.

: Data of selected studies were extracted, and analysis was performed on Review Manager (RevMan), version 5.4. Quality assessment of included studies for potential risk of bias was evaluated using the Newcastle–Ottawa Scale (NOS) for cohort studies. Three cohort studies of spontaneous pregnancies were included. Endometriosis was associated with an increased risk of preeclampsia (RR = 1.45, 95% CI 1.13–1.88, P = .004, I2 = 0%, n=3 studies). A sensitivity analysis excluding a study with adenomyosis cases yielded similar risk (RR = 1.44, 95%CI 1.11–1.87, P = .006, I2 = 0%, n=2 studies). Having endometriosis did not significantly increase risk of caesarean delivery (RR = 1.38, 95%CI 0.99–1.92, P = .06, I2 = 80%, n=2 studies), or post-partum hemorrhage (RR = 1.16, 95%CI 0.46–2.91, P = .76, I2 = 50%, n=2 studies).

: We detected an increased risk of preeclampsia in women with endometriosis who conceived spontaneously. Endometriosis did not appear to increase the risk of caesarean delivery and post-partum hemorrhage, but the number of studies was limited, and the heterogeneity was high.