A UPI report summarizes the findings of a systematic review (a study of studies) of 60 studies comparing the likelihood of deep venous clots and pulmonary embolism (venous thromboembolism) after cesarean delivery versus vaginal birth. Meta-analysis (pooling data from multiple studies) of population-based studies found that cesarean surgery tripled the risk of experiencing a venous clot (odds ratio 3.0) while meta-analysis of studies based on hospital registries found six times the odds (odds ratio 5.9 in studies with confirmed diagnosis). Statistical adjustment to account for maternal age and BMI did little to alter the risk. In addition, the proportion of women experiencing pulmonary embolism among women experiencing a venous clot (49% vs. 31%) was also higher after cesarean. Cesareans during labor conferred more risk than planned cesarean when compared with vaginal birth (odds ratio 2.1 vs. 2.8 after adjustment). The incidence of venous clots after cesarean surgery was 43 per 10,000 overall and 20 per 10,000 in low-risk women.
The UPI report explains that pregnant women in general are at heightened risk for clots because of the rise in clotting factors during pregnancy and from the weight of the uterus compressing the pelvic blood vessels. Surgery itself mobilizes a healing response that includes an increase in the propensity to form clots, and another factor is that some health conditions may increase both risk of clotting and the need for cesarean. The reviewers add that decreased mobility following surgery may also play a role.
Staying mobile in labor would seem a simple, no-risk preventive strategy as would getting up and moving as soon as possible after cesarean surgery. The American College of Obstetricians & Gynecologists recommends placing mechanical pneumatic-compression devices on the legs before surgery for all women and considering anti-clotting medication for women at especially high risk. You may wish to discuss these options with your care provider.