Chicago gene doctors said Tuesday that they can determine if a woman will have a baby with Down’s syndrome before she gets pregnant, provided she is willing to undergo in-vitro fertilization.
Using an experimental technique called polar body analysis, the genetic material of an egg can be checked before laboratory fertilization, helping some women avoid abortions, according to physicians at Illinois Masonic Medical Center.
A relatively common genetic disorder, Down’s strikes 1 out of 600 babies. In 95 percent of all cases, the disorder originates with the egg, not the sperm, and the only known risk factor is advanced maternal age-at age 35, a woman has 1 chance in 117 of having a baby with Down’s; at 40, her odds are 1 in 34.
In the current issue of the journal Human Reproduction, the Chicago researchers reported on a yearlong study involving 100 women who underwent the polar body procedure.
Several already have delivered healthy babies, and more than 20 are pregnant with no sign of Down’s, according to Dr. Yury Verlinsky, director of the Reproductive Genetics Institute at Masonic.
But the possibility exists that the Masonic patients could have achieved the same results without genetic testing. The majority of women who have conventional in-vitro fertilization are older and have normal pregnancies.
Nonetheless, according to Dr. Charles Strom, director of medical genetics at the hospital, “The beauty of the polar body work is it gives a 35-year-old female the same chance of conceiving a chromosomally normal baby that a 21-year-old has.” He said at least half the women in the in-vitro fertilization program are 35 or older.
“The concept is attractive-that we could enhance pregnancy outcomes,” noted Northwestern University geneticist Dr. Eugene Pergament. “However, its efficacy remains far from proven.”
A Northwestern study of almost 5,000 women of advanced maternal age who underwent prenatal testing revealed Down’s in about one pregnancy in a hundred, Pergament said.
Polar body analysis hinges on basic biology.
During normal development, the human egg jettisons a sac of excess chromosomes called the polar body before it gets ready to be fertilized by a male’s sperm.
Verlinsky decided six years ago that this sac, being a mirror image of the egg, could allow him to deduce the genetic content of the egg itself.
He has sought to gain acceptance for the theory ever since. At least four recent scientific papers have questioned its validity, pointed out problems or suggested ways to make it more accurate.
Without such testing, about 30 percent of the Down’s pregnancies resulting from in-vitro fertilization would have miscarried naturally, Verlinsky said, and others could have been picked up by the standard prenatal testing techniques, chorionic villi sampling and amniocentesis.
In-vitro fertilization is expensive, labor intensive and often disappointing. The polar body test would add another $2,000 to $2,500 to its costs, Strom said.
