Response to Letter

In Reply: We thank Dr. Tang and colleagues for their interest in our work in the July 2024 issue.1 They raise the issue of other variables that could be associated with an increased risk of venous thromboembolism (VTE).2,3 However, the focus of our study was not to assess the efficacy of unfractionated heparin (UFH) dosing on VTE prophylaxis (the study was underpowered for this outcome), and other investigators have established efficacy in larger cohorts.4 As a result, these variables were examined but not presented because they did not significantly influence the primary outcome of elevated activated partial thromboplastin time. The letter writers also remark on including rates of stillbirth and ovarian hyperstimulation syndrome, but these diagnoses did not apply to our study cohort of pregnant patients with prolonged antepartum hospitalizations. Dr. Tang et al are correct that renal function can alter heparin deposition and response to UFH.5 We included creatinine and glomerular filtration rate in our baseline laboratory evaluations of all participants, summarized in Table 1 of our study, and there were no significant differences between groups.1 We also performed a multivariate logistic regression adjusting for body mass index (BMI) 30 or higher and creatinine, based on established clinical data that these factors can influence UFH response and may be confounders not detected in our cohort due to small sample size. After adjustment, gestational age–based dosing of UFH remained independently associated with a significantly increased risk of an abnormal activated partial thromboplastin time (adjusted odds ratio 11.23, 95% CI, 1.05–120.49). This was not included in the final article due to concerns for limited interpretation, because our small sample size resulted in wide CIs. Future investigations with larger study cohorts are needed to evaluate the effect of renal function on response to UFH in pregnancy. Finally, we maintained a record of additional medications that were taken by study participants. We reported aspirin use in Table 1 of our study, which was not significantly different between groups.1 There was also no difference in diphenhydramine (P=.44) or ascorbic acid (P=.49) use. However, we did not discuss additional medications individually, because our small study cohort combined with the multiple medications limits the ability to obtain meaningful conclusions from this analysis.