Original reportsPreterm Birth in Relation to Maternal Organochlorine Serum Levels
Introduction
Technical DDT is a mixture of organochlorine compounds (mainly p,ṕ-DDT, o,ṕ-DDT, p,ṕ-DDE and, o,ṕ-DDE) used as an insecticide for malaria control. Although DDT was banned or restricted in industrialized countries in the 1970s, it continued to be used in many tropical countries (1).
Considerable attention has been given to the possible link between p,ṕ-DDE, the most persistent of the p,ṕ-DDT metabolites, and breast cancer but relatively little is known about its potentially adverse reproductive effects.
Reproductive toxicity of p,ṕ-DDT have been reported in animals including premature delivery in rabbits (2) and sea lions (3). Placental transfer has been documented in humans for p,ṕ-DDE, β-hexachlorocyclohexane (β-HCH), and hexachlorobenzene (HCB) (4). Higher serum levels of p,ṕ-DDE have been reported in preterm births as well as spontaneous abortions 5, 6, 7, 8, 9, but all of these studies were based on small populations and generally lacked control of confounding factors. A small age- and race-matched case-control study from the US found no association between p,ṕ-DDE and preterm birth (10). And recently, a study based on the large-scale US Collaborative Perinatal Project (CPP) (11), reported that increasing levels of p,ṕ-DDE increased the risk for preterm birth and, less consistently, the risk for small-for-gestational-age births. Preterm birth is a major determinant of infant mortality (12) and represents an important public health problem in Mexico (13).
Technical DDT was prohibited in Mexico in 1991, nineteen years after it was banned in the United States. Currently, other insecticides are used to control malaria. The use of β-HCH and HCB was also recently restricted in Mexico. Nevertheless, the continued prevalence of p,ṕ-DDE, β-HCH and HCB levels in biological specimens of Mexican residents demonstrates their previous widespread use and their persistence (1).
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Materials and methods
In 1995, we performed a case-cohort study in three large public hospitals located in Mexico City (Hospital Castelazo Ayala, Hospital Tlatelolco, Hospital de la Mujer). From a total of 188 women who were recruited with spontaneous preterm birth, we randomly selected 100 whose serum samples were analyzed for p,ṕ-DDE, β-HCH and HCB. Preterm birth was defined as <37 weeks of gestation with no weight criterion. Gestational age was calculated from the date of the last menstrual period. In this group,
Results
The distributions of maternal age, marital status, maternal education and parity were similar for the preterm and the term births (Table 1).
Among women with previous pregnancies, a history of one or more abortions, preterm birth or low birth-weight tended to be higher for those with preterm as compared with term deliveries. In the total population, women with a pre-pregnancy weight of <50 kg had a two-fold increased risk of preterm birth when compared with those in the reference category of >60
Discussion
A suggestive relationship between serum levels of p,ṕ-DDE and β-HCH and preterm birth was observed in this study, independent of other known risk factors. No effect was found for HCB serum levels.
Since maternal p,ṕ-DDE serum levels are similar throughout pregnancy (16), serum p,ṕ-DDE levels measured at the time of delivery are representative of those in each pregnancy trimester. We found an approximate two-fold increased risk of preterm birth for p,ṕ-DDE (OR = 1.87, 95% CI = 0.95–3.68 for
Acknowledgements
The authors thank Dr. Mary Wolff for helpful information regarding DDT assays, and Ms. Reina Collado for editing this manuscript. This study was supported by the National Council for Science and Technology of Mexico (CONACYT), The Carnegie Foundation, and the Mexican Foundation for Health. Dr. Laura Torres-Arreola is a Selikoff Fellow and Drs. Berkowitz, Torres-Sánchez, and López-Carrillo are faculty associated with the Mount Sinai/Queens College International Training Program in Environmental
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