Dexamethazone, like diethylstilbestrol (DES), which caused fertility problems for mothers and fatal cancers among babies exposed in utero, is a synthetic hormone.
The chemical dose reaching the fetus is 60 to 100 times what the body would normally experience, according to Dreger's report.
About 1 in 10,000 to 18,000 children is born with congenital adrenal hyperplasia, or CAH, according to the Intersex Society of North America in Rohnert Park, Calif. It is the most common disorder of sexual development in females. In boys, it does not affect the genitals, but causes an over-production of the adrenal glands.
CAH occurs when a child carries two recessive genes for the disorder, one from each parent. Couples who carry that silent mutation have a one in four chance of passing it on to a child.
Women who are identified as carrying that gene or have a family history or child with the disorder, are given the drug as early as five-weeks' gestation, before the gender of the child is even known.
And because there is wide variation in how a girl's genitals develop in CAH, there is no way of measuring its effectiveness.
"Treatment is dicey," study author Dreger said. "And when you do the math, 90 percent are exposed who didn't have a need."
As for Janet Green, her mother was pregnant long before doctors treated women at risk with dexamethasone, but she knows the psychological pain that accompanies CAH. She struggled in years of therapy and had two failed marriages.
But Green was also a reproductive "success story," giving birth to two children through C-section. And in mid-life, she came out as a lesbian and has found joy in activism on behalf of those with disorders of sexual development.
Green said doctors like New are doing "some amazing things" for girls with CAH. "She doesn't want them to go through awful surgeries, which is the typical experience," Green said.
But she said use of dexamethasone should stop until further study can prove it is safe.
"Parents have really good intentions," Green said. "But this is something they need to be protected from."