Reported Prevalence of Inherited Thrombophilia in Pregnancy: Impact of Cohort Selection on Screening Implications—A Systematic Review

Background/Objectives: Inherited thrombophilia (IT) has been extensively investigated as a potential contributor to adverse pregnancy outcomes; however, reported prevalence varies widely across studies. This systematic review aimed to evaluate how cohort selection influences the reported prevalence of inherited thrombophilia in pregnancy and to explore the implications of this variability for clinical interpretation and screening practices. Methods: A systematic review was conducted following PRISMA 2020 guidelines. PubMed, Scopus, Web of Science, and Google Scholar were searched. A total of 5480 records were identified, and 7 observational studies (cohort and case–control) met inclusion criteria. Data were synthesized qualitatively due to heterogeneity. Results: Prevalence ranged from 0% to 14%, depending on population characteristics. The largest cohort study reported an inherited thrombophilia prevalence of 8.1%, comparable to the general population. Higher rates were observed in referral-based and antiphospholipid Syndrome (APS)-associated cohorts, while case–control studies showed no significant differences between affected individuals and controls. Ethnic variability was also observed. Conclusions: These findings should be interpreted as patterns observed across heterogeneous study designs rather than as definitive evidence of causality. Current evidence does not clearly support universal screening in pregnancy; however, the findings should be interpreted cautiously because several included studies were limited by small sample sizes and methodological heterogeneity.