Background
Breastfeeding is the perfect way to nourish infants and protect them from illness1. Documented benefits to the nursing mother include a reduction in the risk of breast and ovarian cancer2. Other studies have identified various risk factors associated with a decreased duration of breastfeeding. Among those were smoking habits during pregnancy3, Caesarean delivery4,5, low socio-economic status6,7, low maternal education8, and employment9.
In addition it has been reported that maternal burden of dichlorodiphenyldichloroethylene (DDE), a metabolite of the pesticide dichlorodiphenyltrichloroethane (DDT), is related to a shorter breastfeeding duration possibly by an endocrine disruptive effect10-12. An endocrine disrupter has been defined by U.S. Environmental Protection Agency as “an exogenous chemical substance or mixture that alters the structure or function(s) of the endocrine system and causes adverse effects at the level of the organism, its progeny, populations, or subpopulations of organisms, based on scientific principles, data, weight-of-evidence, and the precautionary principle”13, p. ES-1. The finding that DDE was demonstrated to affect duration of breastfeeding raise the suspicion that oral contraceptives (OC), frequently used endocrine disruptors, may also be associated with breastfeeding duration. Indeed, studies have shown that OC use after pregnancy was related to a decreased duration of breastfeeding4,14. However, no study has yet examined the effect of OC use before pregnancy on length of breastfeeding. The objective of this study was to investigate whether use of OC before pregnancy reduces the total duration of breastfeeding.
Methods
In 1994/95, a three-year follow-up study of school children was initiated to monitor environmental health risk15-19. Parents of 1,091 second grade school children in 18 townships were invited to participate in this study. We obtained permits from the Data Protection Agency of the State of Hamburg, Germany; from the Ministry of Cultural Affairs of Hesse, Germany; and from the local school committees. Informed consent, according to the requirements of the Ethical Committee of the Board of Physicians and the Data Protection Agency of the State of Hamburg, was obtained from all participating parents. The study population consisted of 663 mothers of the index school children residing in Hesse, Central Germany. Women who adopted the index child were not interviewed about breastfeeding.
Trained personnel conducted face-to-face interviews with the mothers, retrospectively ascertaining health and living conditions. The interview questionnaire was based on the standardized questionnaire used in the European Studies on Fertility and Subfecundity20. The following variables were considered in this analysis: mother’s age at delivery (< 20, 20-24, 25-29, > 30 years); mother’s education (high school or less, some college, and college graduate or higher); date of conception, date of delivery, outcome of index pregnancy; maternal age at menarche ( 11 years old, 12–15 years old, > 16 years old); smoking habits during pregnancy (none, yes); planning this pregnancy (no, undecided, yes); and use of OC before pregnancy (none, yes), and its timing before pregnancy (0–3, 4–12 months before conception). Information on the type of OC (combined estrogen/progesterone or progesterone only) or its brand name was not collected. To determine birth order (one, two, three and more), the date of birth of each index child was positioned within the reproductive history of the mother. No mother reported a stillbirth before the birth of the index child. Regarding breastfeeding, we asked whether the child was breastfed, if so, the duration of exclusiv