D-Dimer Variability in the Postpartum Period,

In the United States, venous thromboembolism (VTE) is a leading cause of peripartum morbidity and mortality. The utility of the D-Dimer assay as an aid to the diagnosis of VTE during the postpartum period is unclear. D-Dimer levels are known to increase during pregnancy and no normal ranges have been established. Even less is known about D-Dimer in the postpartum period when most VTEs occur. We examined D-Dimer levels during early and late postpartum periods (one and four weeks respectively) to assess whether D-Dimer levels have a role to play in predicting adverse events postpartum.

Women who gave birth between July 2010 and June 2011 were invited to enroll in the study. In addition to routine demographics, birth data, CBC, ABO blood typing, BMI and social histories, all women answered a 10-item questionnaire. D-Dimer assays were performed at 7–10 days postpartum. Women were encouraged to return for a second D-Dimer test at 4–6 weeks postpartum. Standard reference ranges were used with an upper level cutoff at 0.5μg/ml.

34 women participated in the study and 17 women returned for the late postpartum period. In the immediate postpartum period, 33 of 34 (97%) women had D-Dimer levels higher than the normal nonpregnant range (< 0.5μg/ml). By 4–6 weeks postpartum, D-Dimer had returned to non-pregnant normal levels in 70% of women. There was very high variability in D-Dimer level in the early postpartum periods: levels ranged between 0.45–5.91μg/ml. In the later postpartum period D-dimer levels had decreased substantially but still ranged between 0.1–0.96μg/ml. D-Dimer levels were significantly elevated among women who had undergone cesarean section (C-Section) when compared to women who underwent normal vaginal delivery (2.89μg/ml vs 1.59μg/ml, p=0.01). Although black women were found to have significantly higher D-Dimer levels compared to whites in the immediate postpartum period (Black 2.274μg/ml vs White1.187μg/ml, p=0.006), this difference was found to be secondary to the higher incidence of C-Section among black women, and when this was adjusted for, no difference could be demonstrated. In agreement with this, the later postpartum period sampling did not find a meaningful difference in D-Dimer levels between blacks and whites (0.41μg/ml vs 0.42μg/ml respectively, p=0.93). The only other variable that was found significantly associated with D-Dimer level was breastfeeding: women who breastfed had higher D-Dimer levels than those who did not (2.41μg/ml vs 1.54μg/ml respectively, p=0.04). Maternal age, maternal BMI, newborn weight and maternal blood type were not associated with D-Dimer levels. None of the women who participated in our study were diagnosed with a VTE in the postpartum period.

D-Dimer levels are elevated and highly variable in the immediate postpartum period. D-Dimer levels decrease subsequently and trend toward normal (<0.5μg/ml) by 4–5 weeks postpartum. C-Section delivery method is a major factor increasing D-Dimer levels postpartum. Our findings suggest that higher levels of D-Dimer may be considered normal for the postpartum period and ranges may need to be adjusted for delivery method. Further studies are indicated to help assess if “normal” ranges for D-Dimer in the postpartum period can be determined if the test is to serve a useful diagnostic purpose.

No relevant conflicts of interest to declare.