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Interpregnancy Interval After Termination of Pregnancy and the Risks of Adverse Outcomes in Subsequent Birth.

We used this only as an example to show the variations in the total blood volume but not as the basis of what to be expected as the norm. We would like to reference Table 2 in our study, 1 where the total blood volume and 5, 10, and 15% volumes were calculated for different body surface area quintiles. That was the main purpose of this arti- cle. This was also the reason for not including blood transfusions. Our future direction would be to validate this with quantiﬁed blood loss and assess clinical changes at different percentages of total blood volume lost and blood transfusions. We did group all our pregnant patients together; how- ever, this should not have changed our outcome, because the measurements were all taken on admission and would have been reﬂective of the patient’s cur- rent gestational period. We agree with the authors regarding the existence of multiple confounding factors such as multiple gestation, which was the reason we did not include that group in our study. Financial Disclosure: The authors did not report any potential conﬂicts of interest. Radha Burtch, MD Chantal Scott, MD Departments of Obstetrics and Gynecology, John H. Stroger Jr. Hospital of Cook County and Northwestern University, Feinberg School of Medicine, Chicago, Illinois Lindsay Zimmerman, MPH Department of Obstetrics and Gynecology, John H. Stroger Jr. Hospital of Cook County, Chicago, Illinois Ashlesha Patel, MD Departments of Obstetrics and Gynecology, John H. Stroger Jr. Hospital of Cook County and Northwestern University, Feinberg School of Medicine, Chicago, Illinois REFERENCES 1. Burtch R, Scott C, Zimmerman L, Patel A. Blood loss as a function of body sur- face area: redeﬁning parameters of obstet- ric blood loss. Obstet Gynecol 2016;128: 2. Feldschuh J, Enson Y. Prediction of the normal blood volume. Relation of blood Letters volume to body habitus. Circulation 1977;56(4 pt 1):605–12. 3. Baker RJ, Kozoll DD, Meyer KA. The use of surface area as a basis for establish- ing normal blood volume. Surg Gynecol Obstet 1957;104:183-9. 4. Nadler SB, Hidalgo JU, Bloch T. Predic- tion of blood volume in normal human adults. Surgery 1962;51:224–32. 5. Milosevic N, Popovic J, Grujic Z, Rapaic M. One-compartmental biometric blood loss calculation after cesarean section. Eur J Drug Metab Pharmacokinet 2011; 6. Wang Y, Moss J, Thisted R. Predictors of body surface area. J Clin Anesth 1992;4: Interpregnancy Interval After Termination of Pregnancy and the Risks of Adverse Outcomes in Subsequent Birth We thank the authors for their report 1 but are concerned that the analysis was too simpliﬁed to truly understand the association of interpregnancy interval and subsequent preterm birth. When evaluating the demographic categories, gestational age was grouped as 12 weeks or less compared with more than 12 weeks. This type of categoriza- tion fails to allow an analysis reﬂecting when abortions are performed and to use this analysis, if correct, to properly counsel patients. Approximately 53% of all abortions in the United States are performed at 7 weeks of gestation or less. 2 Grouping together women who undergo abortion at 10 weeks with those who undergo abortion at 6 weeks is potentially inappropriate statistically. For this analysis to have the ability to guide clinical practice, gestational age categories cannot simply be conve- niently packaged into bivariate groups. The authors need to present analyses with clinically applicable ges- tational age ranges such as 7 weeks or less, 8–10 weeks, and 11–14 weeks (all ﬁrst trimester) as well as 15–20 and 21–24 weeks or more in the second trimester. Because the primary out- come was preterm birth, gestational age at the time of abortion (as well as type of abortion, especially in the sec- ond trimester) is potentially the most important confounder and needs the utmost attention during analysis. If the authors do not have sufﬁcient numbers in each group to perform such analyses, this very signiﬁcant limitation needs to be recognized before the information is used clini- cally for patient counseling, espe- cially given the overly weak adjusted association. Financial Disclosure: Dr. Creinin is a consul- tant for Danco Laboratories. The other author did not report any potential conﬂicts of interest. Mitchell D. Creinin, MD Department of Obstetrics and Gynecology, University of California, Davis, Sacramento, California James Trussell, PhD Ofﬁce of Population Research, Princeton University, Princeton, New Jersey REFERENCES 1. Mannisto J, Bloigu A, Gissler M, Heikinheimo O, Niinimaki M. Inter- pregnancy interval after termination of pregnancy and the risks of adverse outcomes in subsequent birth. Obstet Gynecol 2017;129:347–54. 2. Jatlaoui TC, Ewing A, Mandel MG, Sim- mons KB, Suchdev DB, Jamieson DJ, et al. Abortion surveillance—United States, 2013. MMWR Surveill Summ 2016;65:1–44. In Reply: We thank Mitchell D. Creinin and James Trussell for their interest in our work. 1 In the analyses presented in our article, the gestational age at termination of pregnancy and the method of termination (medical com- pared with surgical) were used to adjust for the confounders and to ensure the comparability of the dif- ferent termination-to-subsequent conception interval groups. Thus, these variables were included in the models, but the results were not pre- sented according to them. After Drs. Creinin and Trussell raised a concern about the categorization of gesta- tional age at termination of preg- nancy, we re-analyzed our data by using a new division of gestational age at termination: 7 weeks or less, 8–12 weeks, 13–20 weeks, and 21– 24 weeks. The ﬁrst two groups repre- sent the ﬁrst-trimester terminations, and the latter two groups represent the second-trimester terminations. The new categorization of gestational OBSTETRICS & GYNECOLOGY Copyright a by The American College of Obstetricians and Gynecologists. Published by Wolters Kluwer Health, Inc. Unauthorized reproduction of this article is prohibited.