Pregnancy-associated venous thromboembolism in sub-Saharan Africa: a case-control study and descriptive analysis of clinical phenotypes

Background: Venous thromboembolism (VTE) is a leading cause of maternal mortality worldwide, yet data on pregnancy-associated VTE (PA-VTE) in sub-Saharan Africa remain limited. Objectives: This study aimed to identify clinical predictors and describe the phenotypic characteristics of PA-VTE in a Tanzanian referral setting. Methods: We conducted a retrospective case-control study at Muhimbili National Hospital from 2016 to 2024. Cases were pregnant or postpartum women (≤6 weeks) with objectively confirmed VTE. Controls were matched 1:2 on gestational stage. Due to sparse data in several matched sets, multivariable analysis was conducted using Firth penalized logistic regression to account for separation and small-sample bias. VTE cases were further characterized descriptively. Results: Of 321 women included (107 cases and 214 controls), independent predictors of PA-VTE were a history of VTE (adjusted odds ratio [aOR], 122; 95% CI, 2.66-43,361), gross varicose veins (aOR, 31.5; 95% CI, 5.98-306), and stillbirth (aOR, 15.2; 95% CI, 1.75-213), with wide CIs reflecting small-sample sizes. DVT accounted for 73% of cases, predominantly proximal and left-sided. Pulmonary embolism was submassive or massive in over one-third of cases. Only 2.8% of women received any thromboprophylaxis—all postpartum—and thrombophilia testing was rarely performed (3.7%). Conclusion: Traditional risk factors—particularly prior VTE, varicose veins, and stillbirth—remain highly relevant in this setting. Uptake of antenatal thromboprophylaxis was very low, highlighting major care gaps. While causality cannot be inferred, these findings underscore the need for larger studies to confirm risk associations and provide foundational evidence. Interventions should focus on developing local guidelines, strengthening clinician awareness, and integrating context-specific risk assessment tools into obstetric care in sub-Saharan Africa.