Subfertility and prepregnancy overweight/obesity: possible interaction between these risk factors in the etiology of congenital renal anomalies.

BACKGROUND: Maternal subfertility and high body mass index (BMI) are both associated with adverse reproductive outcomes, including some birth defects. One study reported an association between subfertility and renal anomalies (Li, 1999).
METHODS: We defined subfertility as the mother's report that she sought fertility treatment from a doctor/clinic, and high BMI as a prepregnancy BMI > or = 25. We included 169 infants with renal anomalies (renal agenesis [n = 41], obstructive defects [n = 117], and duplication defects [n = 11]) and 2763 infants without defects who were born in 1968-1980 in metropolitan Atlanta, after excluding mothers who reported diabetes. Conditional logistic regression (matching variables: race, birth hospital, and birth period) was used to obtain effect estimates (adjusted for maternal age and gestational age).
RESULTS: Subfertility was more common among case-mothers (11.8%) than control-mothers (7.8%), high BMI was similar among case-mothers (11.2%) and control-mothers (10.9%), and joint exposure (subfertility and high BMI) was reported by 3% case-mothers and 0.7% of control-mothers. Joint exposure to subfertility and high BMI was associated with renal anomalies (odds ratio [OR] = 5.8; 95% confidence interval [CI] = 2.0-16.3). All case-mothers who reported a joint exposure had infants with obstructive renal anomalies (OR = 8.5; 95% CI = 2.9-24.7). There was no association observed for either exposure alone (subfertility and low BMI, or high BMI and no subfertility) for either all renal anomalies or obstructive defects.
CONCLUSIONS: Women who are overweight/obese and experience subfertility may be more likely to have an infant with an obstructive renal anomaly. Further exploration of possible biologic mechanisms is needed.