ATLANTA -- A doubling in the rate of boys born with a common defect in which the urinary opening is misplaced on the penis has baffled government scientists.
A sampling of U.S. hospitals found that the rate of hypospadias jumped from 40 cases per 10,000 male births in 1970 to 79 per 10,000 in 1993, the Centers for Disease Control and Prevention reported Wednesday in the November issue of Pediatrics.
A total of 49,162 cases of hypospadias were reported in the United States between 1970 and 1993 among the 763,000 births in hospitals that were monitored for the disease.
The defect rates increased around the country. The highest was reported in the Southeast: from 36 per 10,000 boys in 1970 to 100 per 10,000 in 1993.
Hypospadias, which now affects about 1 of every 100 newborn boys, occurs when the urinary opening is not at the end of the penis.
In its mildest form, the opening is under the head of the penis. In severe cases, it is as far away as the scrotum. Surgery can correct the defect, the earlier the better.
The cause of the defect isn't known but is believed to be linked to an insufficient surge of testosterone 9 to 12 weeks after conception. Testosterone is key to the development of the male reproductive system.
The increases the CDC documented are the first outside of Europe, where hypospadias rates sharply rose in Denmark, England, Hungary, Norway and Sweden in the 1970s and '80s.
Several studies in the 1970s attempted to link those surges to the hormone progestin in oral contraceptives taken by the babies' mothers. A 1967 study found that progestin causes the defect in rats.
The CDC researchers doubt that could account for such increases. That leaves them with no explanation for the U.S. trend.
"We felt it was worth getting this information out in spite of the fact that we could not explain the increase," said Dr. Leonard J. Paulozzi, a CDC epidemiologist and lead author of the Pediatrics article.
Some reproductive experts suggest other theories: More pediatric urologists may be trained to look for the defects, so there are more reports. Also, test-tube fertilization might also lead to an excess of female hormones that would create a hormone imbalance in the fetus.
"If a change like this is occurring in a short period of time, clearly it's likely that something we are doing in our environment or medically may be the cause of the change," said Dr. Peter Schlegel, an associate professor of urology at Cornell University Medical College.