A 32-year-old woman, gravida 2 para 1, comes to the office for a routine prenatal visit. The patient had a postpartum hemorrhage (PPH) after her first pregnancy and is worried about the possibility of PPH after her scheduled repeat cesarean delivery. She read about the effectiveness of prophylactic tranexamic acid in reducing the risk of hemorrhage after scheduled cesarean delivery and wants to discuss the results. The outcomes of the study were PPH, clinical and laboratory (blood samples at day 2) measurements of postpartum blood loss, and several adverse events after scheduled cesarean delivery at ≥34 weeks gestation. Patients received intravenous infusion of a uterotonic agent and either tranexamic acid or saline placebo within 3 minutes after cesarean delivery. A summary of the results is shown in the table below. Based on the study results, which of the following conclusions is strongly justified?

Question

A 32-year-old woman, gravida 2 para 1, comes to the office for a routine prenatal visit.  The patient had a postpartum hemorrhage (PPH) after her first pregnancy and is worried about the possibility of PPH after her scheduled repeat cesarean delivery.  She read about the effectiveness of prophylactic tranexamic acid in reducing the risk of hemorrhage after scheduled cesarean delivery and wants to discuss the results.  The outcomes of the study were PPH, clinical and laboratory (blood samples at day 2) measurements of postpartum blood loss, and several adverse events after scheduled cesarean delivery at ≥34 weeks gestation.  Patients received intravenous infusion of a uterotonic agent and either tranexamic acid or saline placebo within 3 minutes after cesarean delivery.  A summary of the results is shown in the table below.  Based on the study results, which of the following conclusions is strongly justified?

Quizplus · Accepted Answer

Explanation: Relative risk (RR) is a measure of association used to compare the risk of outcome in an exposed (eg, treatment) group relative to a nonexposed (eg, placebo) group: RR = (risk of outcome in exposed group) / (risk of outcome in nonexposed group) RR = (risk of outcome in exposed group) / (risk of outcome in nonexposed group) The RR may be interpreted as follows: RR < 1.0: Exposure is associated with a decrease in the risk of outcome compared to no exposure. RR = 1.0 (null value): There is no association between the exposure and the outcome. RR > 1.0: Exposure is associated with an increase in the risk of outcome compared to no exposure. The confidence interval (CI) of an RR indicates, with a certain confidence level, whether a given RR is statistically different from the null value (ie, RR = 1.0). A CI that includes the null value is not statistically significant, and a CI that excludes the null value is statistically significant (at that confidence level). In this study, results show that prophylactic use of tranexamic acid reduces the risk of postpartum hemorrhage (PPH) relative to placebo because RR < 1.0; the change (RR = 0.840 compared to RR = 1.0) represents a relative decrease of (1.0 − 0.840)/1.0 = 0.160, or 16%. Similarly, prophylactic use of tranexamic acid reduces the risk of peripartum hemoglobin decrease >2 g/dL by 21% (RR = 0.790; 95% CI: 0.705-0.891) and peripartum hematocrit decrease >10 percentage points by about 30% (RR = 0.705; 95% CI: 0.517-0.959) (Choice C). Because none of the CIs includes the null value (ie, RR = 1.0), these associations are statistically significant (Choice E). (Choices A and B) Prophylactic use of tranexamic acid does not appear to be significantly associated with clinically significant PPH (RR = 0.922; 95% CI: 0.797-1.065), additional use of uterotonic agents for excessive bleeding (RR = 0.814; 95% CI: 0.650-1.018), or blood transfusions (RR = 1.071; 95% CI: 0.695-1.649) because each CI contains the null value of 1.0. Educational objective: Relative risk (RR) is a measure of association between an exposure and an outcome. For RR < 1.0, the exposure decreases the risk of the outcome (ie, protective factor). For RR = 1.0, there is no association between exposure and the outcome. For RR > 1.0, the exposure increases the risk of the outcome. Confidence intervals that contain the null value (ie, RR = 1.0) indicate that the association is not statistically significant.

A 32-Year-Old Woman, Gravida 2 Para 1, Comes to the Office