Am J Epidemiol 2003; 158:825.
Copyright © 2003 by Johns
Hopkins Bloomberg School of Public Health
LETTERS TO THE EDITOR |
THREE AUTHORS REPLY
1 Department of Epidemiology, University of Iowa College of Public Health, Iowa City, IA 52242
2 Division of Epidemiology, Statistics, and Prevention Research, National Institute of Child Health and Human Development, Bethesda, MD 20892
We thank Dr. Basso for clarifying that her study of paternal change, interbirth interval, and risk of preeclampsia in multiparous women did consider the effect of registered abortions between the first and second births but failed to find a protective effect (1, 2).
It is important to note key differences between our study (3) and those like Dr. Basso’s, which have relied on registry data from Denmark (2) and Norway (4, 5). The Calcium for Preeclampsia Prevention (CPEP) Study conducted prospective surveillance of nulliparous women for the development of preeclampsia, defined according to standardized criteria (6). In contrast, the Danish and Norwegian studies analyzed changed paternity among multiparous women, and the complex diagnosis of preeclampsia relied on hospital discharge codes covering 15- and 32-year periods, respectively. Unfortunately, despite their large numbers of subjects, registry-based studies are vulnerable to residual confounding by important risk factors for preeclampsia, such as body mass index, which are not recorded in the registry data. Although smoking during pregnancy was considered in the study by Basso et al. (2), the Norwegian studies (4, 5) did not, although it is inversely related to preeclampsia risk.
Because women who change partners are likely to have longer intervals between births, future studies should attempt to ascertain all induced and spontaneous abortions, including those preceding the first birth. In addition, data on paternity, conception date, and gestational age at termination should be collected. Women in unstable relationships are more likely to obtain induced abortions than women in stable unions (7). Therefore, studies that fail to consider abortion type, paternity, and timing of abortive outcomes in their analyses are subject to possible bias from confounding, and they are more apt to attribute erroneously long interpregnancy intervals to women who change partners.
REFERENCES
- Basso O. Re: "Abortion, changed paternity, and risk of preeclampsia in nulliparous women." (Letter). Am J Epidemiol 2003;158:825.
- Basso O, Christensen K, Olsen J. Higher risk of pre-eclampsia after change of partner. An effect of longer interpregnancy intervals? Epidemiology 2001;12:624–9.[CrossRef][Web of Science][Medline]
- Saftlas AF, Levine RJ, Klebanoff MA, et al. Abortion, changed paternity, and risk of preeclampsia in nulliparous women. Am J Epidemiol 2003;157:1108–14.
[Abstract/Free Full Text] - Trogstad LIS, Eskild A, Magnus P, et al. Changing paternity and time since last pregnancy; the impact on pre-eclampsia risk. A study of 547,238 women with and without previous pre-eclampsia. Int J Epidemiol 2001;30:1317–22.
[Abstract/Free Full Text] - Skjaerven R, Wilcox AJ, Lie RT. The interval between pregnancies and the risk of preeclampsia. N Engl J Med 2002;346:33–8.
[Abstract/Free Full Text] - Levine RJ, Esterlitz JR, Raymond EG, et al. Trial of Calcium for Preeclampsia Prevention (CPEP): rationale, design, and methods. Control Clin Trials 1996;17:442–69.[CrossRef][Web of Science][Medline]
- Skjeldestad FE, Borgan JK. Trends in induced abortion during the 12 years since legalization in Norway. Fam Plann Perspect 1994;26:73–6.[CrossRef][Web of Science][Medline]
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