The most common male-genital birth defect is undescended testicles, affecting about 3 percent of boys born in the United States. A few risk factors have been identified, but researchers have generally puzzled over the cause of the problem. Now, a new study has revealed an unexpected risk factor. Regular alcohol consumption during pregnancy appears to triple the risk that a woman's son will have the condition, Ida Damgaard and her colleagues report in the February 2007 Environmental Health Perspectives. Their article appeared online Dec. 4, 2006.
The finding suggests an obvious strategy for reducing the incidence of the birth defect: Women should be even more strongly discouraged from drinking during pregnancy. But Damgaard's group has its eye on a bigger prize. The researchers are trying to understand the reasons behind declining fertility rates in Western countries. Boys born with undescended testicles are 60 percent more likely than other boys to be infertile when they grow up. Furthermore, the researchers believe that poor testicular development in the uterus may lead to later fertility problems even in boys who don't show the genital abnormality at birth.
Male fertility has been declining dramatically in developed countries over the past 40 years, with sperm density dropping 1.5 percent per year in the United States and 3 percent per year in Europe and Australia. That change, combined with the tendency of Western women to delay getting pregnant until after their fertility peaks, has meant that more and more couples have had difficulty getting pregnant.
The rate of undescended testicles in newborn boys has increased steadily over about the same period. The defect is known as cryptorchidism from the Greek: "crypto" means hidden, and "orchid" means testes.
The study is one of many coming out of a 10-year-old effort to track nearly 5,000 pregnant women in Denmark and Finland and then their children. The pregnant women were asked about their consumption of alcohol and caffeine, working conditions, diet, and medical history: "anything we could think of," says Katharina Main, a coauthor of the paper and a pediatrician at Rigshospitalet in Denmark. When the babies were born, the researchers examined them and found that 128 of the boys were cryptorchid.
Boys from mothers who had five or more alcoholic drinks per week during pregnancy had triple the rate of cryptorchidism of boys whose mothers didn't drink at all. The researchers didn't see a significant effect in women who drank less than five drinks a week, but Main says she suspects that alcohol can have an impact even at lower rates of consumption. "I wouldn't say that four [drinks are] OK but five aren't," Main says.
In three-quarters of the cryptorchid boys, the testes descended into their natural place within 3 months after birth. A quarter of the boys needed surgery to correct the problem. But even boys whose testes descended on their own showed a lasting abnormality. "We're still worried about these babies . . . because when we look at the hormones, they still show an impairment of hormone production," Main notes. Even if a boy's testicles descend on their own so he doesn't need surgery, "it isn't a sign that everything is OK."
Damgaard's group is doing numerous studies using data from the women and their babies. Early last year, the team identified another risk factor for cryptorchidism: maternal exposure to pesticides, including DDT, that are no longer in regular use but that persist in the environment. Previously known risk factors include premature birth, low birth weight, gestational diabetes, and being a twin. Damgaard's group is searching for even more risk factors for the condition.
Interest in cryptorchidism is high in Denmark because the defect is unusually common there. About 9 percent of boys born in the country have the problem, compared with just 2.3 percent of the boys born in neighboring Finland.
The identification of alcohol consumption as a risk factor helps to explain this anomaly. In Denmark, public information campaigns have encouraged pregnant women to limit their alcohol consumption but not to eliminate it entirely, whereas Finland and most other countries advise women to abstain entirely while they're carrying babies.
Katharina M. Main
University of Copenhagen
Department of Growth and Reproduction