Recruitment prior to conception for pregnancy studies: a systematic review and meta-analysis.

Abstract

OBJECTIVE: Pregnancy outcomes may be improved by optimizing preconception health; however, designing preconception research studies presents distinct challenges. These include estimating feasible recruitment, attrition, and expected pregnancy rates. We systematically reviewed existing preconception studies to quantify recruitment rates, retention, and pregnancies to inform feasibility assessments and sample size calculations for future preconception and pregnancy-related research. DATA SOURCES: NHS Knowledge Hub, TRIP database, Cochrane Library, PubMed, MEDLINE, Embase, CINAHL, Emcare, Web of Science, Scopus, ASSIA, and PsycINFO were searched (database inception-September 2025). STUDY ELIGIBILITY CRITERIA: Eligible studies reported recruitment of nonpregnant women intending to conceive into studies reporting at least one pregnancy outcome. STUDY APPRAISAL AND SYNTHESIS METHODS: Risk of bias and quality assessment were performed using the Newcastle-Ottawa Scale and Cochrane Risk of Bias tool, followed by the Grading of Recommendations Assessment, Development and Evaluation framework. Statistical analysis was performed in R v4.4.1. RESULTS: 79 studies (n=117,603 participants; n=53,838 pregnancies) were included. Overall, risk of bias was fair across studies. The heterogeneity across all meta-analyses was high. Recruitment via healthcare settings yielded higher weekly recruitment than other methods (median 9 participants/week; interquartile range, 4-19), compared with studies using only non-healthcare-based recruitment methods (2; interquartile range, 2-4). Weekly recruitment was higher in larger studies and in low- and middle-income countries compared to high-income countries. Attrition prior to conception was lower in observational than in interventional studies and among those with fertility issues compared to those with other medical comorbidities. Among participants who conceived, retention during pregnancy was high across all studies (97.7%; interquartile range, 95.2-99.0), with higher retention in interventional than in observational studies. CONCLUSION: This review provides a quantitative synthesis of recruitment and retention patterns in preconception research, addressing a critical but understudied period to improve maternal and child health. We found that participant characteristics, recruitment strategy, and study design substantially influence recruitment rates, preconception attrition, and pregnancy retention, with important implications for feasibility assessment, anticipated loss to follow-up, and sample size estimation. Our findings highlight the need for recruitment of diverse populations and methodological tools tailored to preconception research. These findings offer empirically grounded parameters to support the design of more efficient, inclusive, and adequately powered preconception and pregnancy-related studies.