Decrease in anogenital distance among male infants with prenatal phthalate exposure

Environmental Health Perspectives, August, 2005 by Shanna H. Swan, Katharina M. Main, Fan Liu, Sara L. Stewart, Robin L. Kruse, Antonia M. Calafat, Catherine S. Mao, J. Bruce Redmon, Christine L. Ternand, Shannon Sullivan, J. Lynn Teague

Boys' genital examinations included a description of the testes and scrotum, location and size of each testicle, and measurement of the penis. The placement of each testicle was initially coded in six categories; in the present analysis, boys are dichotomized into those with normal testicular descent (placement of both testes coded as normal or normal retractile) or with incomplete testicular descent (all other cases). The scrotum was categorized as distinct from surrounding tissue or not, and by size (small or not). Penile width and (stretched) length were recorded, and penile volume [proportional to [(penile width/2).sup.2] x penile length] was calculated. We recorded the AGD, measured from the center of the anus to the anterior base of the penis. We also recorded the anoscrotal distance (ASD), measured from the center of the anus to the posterior base of the scrotum. This latter measurement was used by Salazar-Martinez et al. (2004), who refer to it as AGD.

Phthalate metabolite analysis. Urinary phthalate metabolite analyses were carried out by the Division of Laboratory Sciences, National Center for Environmental Health, Centers for Disease Control and Prevention (CDC), which had no access to participant data. The analytical approach for the analysis of urinary phthalate metabolites (Silva et al. 2004b) is a modification of previously published methods (Silva et al. 2003). The analysis involves the enzymatic deconjugation of the phthalate metabolites from their glucuronidated form, automated on-line solid-phase extraction, separation with high-performance liquid chromatography, and detection by isotope-dilution tandem mass spectrometry. This high-throughput method allows for the simultaneous quantification in human urine of the nine phthalate metabolites reported in this work. Limits of detection (LOD) are in the low nanogram per milliliter range. Isotopically labeled internal standards were used along with conjugated internal standards to increase precision and accuracy of the measurements. The method is accurate (spiked recoveries are near 100%), and precise with between-day relative standard deviations of < 10%. Quality control (QC) samples and laboratory blanks were analyzed along with unknown samples to monitor performance of the method. The metabolite concentrations reported here are from 85 prenatal maternal urine samples of a total of 214 that also included postnatal maternal and baby samples from the same mothers and their children. The 214 samples were analyzed for phthalate metabolites in six batches, none of which had to be re-extracted for QC failures. Of the 214 samples, seven were re-extracted using < 1 mL of urine because concentrations of MEP calculated using 1 mL were above the linear range of the method.

Statistical analysis. After examining descriptive and summary statistics for all study variables, we explored models for AGD. We fit several alternative measures of body size (weight, height, and body mass index) and both additive and multiplicative functions of these. We defined the anogenital index [AGI = aGD/weight (mm/kg)] as a weight-normalized index of AGD.