This systematic review was reported per the Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) guidelines [9]. It adhered to a protocol registered with PROSPERO (International Prospective Register of Systematic Reviews) under registration number CRD42024506450. The protocol outlined the research question, objectives, inclusion and exclusion criteria, and the methodological approach for this systematic review.

To identify relevant studies addressing the prevalence and maternal–fetal outcomes of PE and eclampsia in pregnant women in Nigeria, we conducted a systematic search across PubMed, Google Scholar, Science Direct, African Journals Online (AJOL), Directory of Open Access Journals (DOAJ), and the Cochrane Library (Fig. 1). We employed a combination of Medical Subject Headings (MeSH) terms and free-text terms related to PE, eclampsia, maternal and perinatal outcomes, pregnancy, and Nigeria. Boolean operators (“AND” and “OR”) were used to refine the search strategy and ensure comprehensive coverage. The search was restricted to studies published from January 1990 to February 2024 (1990 was selected as a cutoff as studies on this topic were published upwards from this period) (Supplementary File 1).

Prevalence of preeclampsia: we included studies that reported the prevalence of PE, defined according to standard diagnostic criteria [3]. Data extraction focused on prevalence rates across different settings, including hospitals, antenatal clinics, and community-based surveys. Studies were reviewed for their diagnostic criteria, sample size, and geographical coverage to ensure consistency in the data collected.

Prevalence of eclampsia: the search identified studies reporting on the prevalence of eclampsia, characterized by the onset of seizures in the context of PE [5]. We assessed how eclampsia cases were defined and reported, including diagnostic criteria and methods of seizure detection. The prevalence rates were extracted and analyzed, noting any variations based on study design or regional differences.

Maternal mortality: to evaluate maternal mortality associated with PE and eclampsia, we included studies that documented maternal deaths, specifying causes related to these conditions. We examined the methods used for reporting maternal mortality, including the criteria for death classification and the documentation of contributing factors. Mortality rates were summarized and analyzed for trends and potential influencing factors such as healthcare access and management practices.

Fetal mortality: we reviewed studies reporting fetal mortality or stillbirth rates in the context of PE and eclampsia. The criteria for defining fetal death and the methods of reporting were analyzed. Fetal mortality rates were extracted and compared across studies, with attention to factors influencing these outcomes, such as prenatal care and delivery management.

Complications: complications associated with PE and eclampsia were extracted from the included studies, focusing on both maternal and fetal outcomes. We categorized complications such as HELLP syndrome, placental abruption, and intrauterine growth restriction (IUGR). The frequency and types of complications reported were summarized, and their impact on maternal and fetal health outcomes was discussed.

To ensure the retrieval of relevant studies, we applied filters and limits based on predefined inclusion criteria. Acceptable study designs included observational studies (cross-sectional, cohort, case–control) and clinical trials. The focus was on studies involving pregnant women in Nigeria, with outcome measures reporting prevalence rates of PE and eclampsia alongside associated maternal and perinatal outcomes. Exclusion criteria were established to maintain the review’s scope. Studies conducted outside Nigeria, those lacking relevant outcome data on PE and eclampsia, and non-research materials such as review articles, editorials, commentaries, and conference abstracts were excluded.

Independent reviewers (A.E.B and N.A) screened titles and abstracts to determine eligibility following the predetermined inclusion and exclusion criteria registered in the PROSPERO protocol. Potentially eligible studies underwent a full-text review, and discrepancies between reviewers were resolved through discussion or involvement of a third reviewer (E.K).

Our focus was on studies involving pregnant women residing in Nigeria who had been diagnosed with preeclampsia and/or eclampsia. There were no restrictions based on age, parity, or gestational age at diagnosis.

The intervention/exposure of interest in this systematic review is preeclampsia and eclampsia among pregnant women in Nigeria.

Maternal outcomes were defined as the adverse health effects experienced by pregnant women diagnosed with preeclampsia or eclampsia in Nigeria. These outcomes were measured by assessing the incidence of complications such as hypertension, proteinuria, eclampsia, HELLP syndrome, renal failure, and maternal mortality. Measurement occurred from diagnosis until postpartum follow-up, as documented in the included studies. Perinatal outcomes refer to the health outcomes of newborns and fetuses born to mothers with preeclampsia or eclampsia in Nigeria. These outcomes were measured by evaluating the incidence of preterm birth, low birth weight, neonatal intensive care unit (NICU) admissions, stillbirth, neonatal mortality, and long-term developmental issues. Measurement occurred from birth until postnatal follow-up, as reported in the included studies.

To ensure a rigorous and unbiased review process, two independent reviewers (A.E.B and N.A) screened all retrieved titles and abstracts against the predefined inclusion and exclusion criteria. Disagreements were resolved through discussion with a third reviewer (E.K) as necessary. Following the initial screening, a full-text assessment of eligible articles was conducted by independent reviewers. This comprehensive analysis ensured all inclusion criteria were met. Any disagreements during full-text review were addressed through discussion or consultation with another reviewer.

Data extraction involved collecting relevant information from each included study. This included bibliographic details (authors, publication year), study design, location, and study duration. Additionally, data were extracted on sample size, prevalence of preeclampsia/eclampsia, maternal mortality rate, mode of delivery, and prevalence of specific maternal complications such as acute kidney injury, cerebrovascular accidents, and puerperal sepsis. Fetal complications were also documented, including the prevalence of fetal mortality (intrauterine fetal death (IUFD), stillbirths, and neonatal deaths), gestational age/prematurity, and admission to the Special Care Baby Unit (SCBU).

The quality assessment of the included studies was done by N.A using the ROBIN-E tool (Fig. 2).

A combination of narrative synthesis and meta-analysis was employed where applicable to synthesize the extracted data. Relevant data from each included study were systematically extracted, focusing on prevalence rates of preeclampsia/eclampsia and associated maternal–fetal outcomes among pregnant women in Nigeria. For clarity and coherence, the extracted data were tabulated to provide a comprehensive overview of various study characteristics, participant demographics, diagnostic criteria for preeclampsia/eclampsia, sample sizes, prevalence rates, and maternal and fetal health outcomes. Meta-analysis models such as the random-effects or fixed-effects models were utilized based on the level of heterogeneity observed among studies. Statistical heterogeneity was assessed using measures like the I2 statistic, with values above 50% indicating substantial heterogeneity. Subgroup analyses were performed to explore potential sources of heterogeneity based on study characteristics such as geographic region, study quality, and diagnostic criteria for preeclampsia/eclampsia. Statistical analysis and meta-analysis were performed using appropriate software packages such as R, STATA.