Maternal endometriosis and genital malformations in boys: a Danish register-based study

OBJECTIVE: To investigate the association between maternal endometriosis and occurrence of the genital anomalies cryptorchidism and hypospadias in sons. DESIGN: Population-based cohort study. SETTING: Not applicable. PATIENT(S): All live-born singleton boys born from 1978 to 2012. INTERVENTION(S): None. MAIN OUTCOME MEASURE(S): Cryptorchidism and hypospadias in boys based on information from the Danish National Patient Register. RESULT(S): The study included 1,073,026 live-born singleton boys. A total of 6,443 boys were sons of women diagnosed with endometriosis before pregnancy. Altogether, 27,342 boys were diagnosed with cryptorchidism, of whom 16,446 had corrective surgery. Hypospadias was diagnosed in 4,853 boys. As compared with unexposed boys, a tendency towards a slightly higher occurrence of cryptorchidism was observed among boys of women with endometriosis (adjusted hazard ratio [aHR] 1.18; 95% confidence interval [CI], 0.97, 1.44). When stratified by medically assisted reproduction (MAR) technologies, the association was slightly stronger among boys born to women with endometriosis who had conceived via MAR, yet it remained moderate and statistically insignificant (aHR 1.27; 95% CI, 0.86; 1.88). When women who conceived with MAR were excluded, the association between endometriosis and cryptorchidism disappeared. For hypospadias, we observed no association, either in the main analysis or the stratified analysis. CONCLUSION(S): The findings from this register-based study do not provide strong evidence for a higher occurrence of the studied genital anomalies among boys of women with endometriosis.