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Luisa Torres-Sánchez,¹ Stephen J. Rothenberg,^1,2 Lourdes Schnaas,³ Mariano E. Cebrián,⁴ Erika Osorio,³ Maria del Carmen Hernández,³ Rosa M. García-Hernández,⁴ Constanza del Rio-Garcia,¹ Mary S. Wolff,⁵ and Lizbeth López-Carrillo¹

¹Instituto Nacional de Salud Pública, Morelos, México; ²Depto. Ecología Humana, CINVESTAV, Merida, Yucatán, México; ³Instituto Nacional de Perinatología, México DF, México; ⁴Sección Externa de Toxicología, CINVESTAV, México, DF, México; ⁵Community Medicine, Division of Environmental and Occupational Medicine, Mount Sinai School of Medicine, New York, New York, USA

Abstract
Background: Evidence suggests that p,p´-dichlorodiphenyldichloroethene (DDE) affects neurodevelopment in infants, although a critical exposure window has not yet been identified.

Objectives: Our goal was to assess the prenatal DDE exposure window and its effect on the psychomotor development index (PDI) and mental development index (MDI) during the first year of life.

Methods: We recruited 244 children whose pregnancies and deliveries were uncomplicated, and whose mothers were monitored throughout the pregnancy. Participating mothers were not occupationally exposed to DDT (dichlorodiphenyltrichloroethane) but were residents of a zone in Mexico with endemic malaria. We measured serum levels of DDE before pregnancy and during each trimester of the pregnancy. We evaluated PDI and MDI of the Bayley Scales for Infant Development (BSID-II) , at 1, 3, 6, and 12 months of age. We adjusted for quality of the home environment and maternal intellectual coefficient (IQ) . We used generalized mixed-effects models for statistical analysis.

Results: Third-trimester DDE level (7.8 ± 2.8 ppb) was significantly higher than the level at baseline, first, and second trimesters, but the differences never exceeded 20%. Only DDE levels during the first trimester of pregnancy were associated with a significant reduction in PDI (every doubled increase of DDE level reduced the PDI 0.5 points) . DDE was not associated with MDI.

Conclusions: A critical window of exposure to DDE in utero may be the first trimester of the pregnancy, and psychomotor development is a target of this compound. Residues of DDT metabolites may present a risk of developmental delay for years after termination of DDT use.

Key words: Bayley scale, breast-feeding, cohort, in utero exposure, infant neurodevelopment, Mexico, organochlorines, p, p´-DDE. Environ Health Perspect 115:435–439 (2007) . doi:10.1289/ehp.9566 available via http://dx.doi.org/ [Online 16 January 2007]

Address correspondence to L. López-Carrillo, Instituto Nacional de Salud Pública, Av. Universidad 655, Col Sta. Maria Ahuacatitlán, CP:62508, Cuernavaca, Morelos, México. Telephone and fax: (777) 311-2338. E-mail: lizbeth@insp.mx

This study was supported by Conacyt (31034-M ; 41708) and Fogarty–Mount Sinai School of Medicine/Queens College International Training and Research in Environmental and Occupational Health Program (D43TW00640) . We also appreciate the financialcontributions from Kellog's of Mexico and Daimler Chrysler.

The authors declare they have no competing financial interests.

Received 1 August 2006 ; accepted 16 January 2007.