Mothers who ate a vegetarian diet during pregnancy had a five-time greater risk of delivering a boy with hypospadias, a birth defect of the penis. The research team suggests that phytoestrogens, hormone-like compounds found in soy, may be responsible for the link.

Interestingly, the researchers also found that mothers who took iron supplements and those who had influenza in the first 3 months of pregnancy also had a higher risk of having a baby boy with hypospadias. The authors suggest that more research is needed to see if any of the associations found in the study actually cause the birth defect.

It is important to note that there is biological evidence that vegetarians have a greater exposure to phytoestrogens and thus a causal link is biologically feasible.

Hypospadias is a birth defect where the opening of the penis is found on the underside of the penis rather than at the tip. It is a common congenital defect, affecting about 1 in 300 newborn males. The condition requires surgery to correct it, where the foreskin is used to repair the problem. Untreated, it can interfere with urination and sexual function.

The investigators asked mothers to fill out questionnaires during pregnancy regarding obstetric history, lifestyle, and dietary practices. Of 7,928 boys born to mothers participating in the study, 51 cases of hypospadias were identified.

Mothers with a vegetarian diet in the first half of pregnancy had a 4.99 times greater risk of having a boy with hypospadias compared with mothers who included meat in their diets, the researchers report. In addition, mothers who took iron supplements had double the normal risk of having a boy with hypospadias, and influenza during the first 3 months of pregnancy increased the risk of by just over three times.

BJU International January 2000;85:107-113