Signs of trouble ahead

New research and changing public attitudes may have opened a Pandora's box of potential problems-some of them as yet only dimly seen.

by JOAN BECK

Sex is determined at the instant of conception by whether the ovum (with its female X chromosome) is first penetrated by a sperm with an X or a male Y chromosome. An ejaculation contains millions of each kind of sperm.

Every cell in the body of the newly conceived child will then have the female XX pattern or the male XY blueprint. It is relatively easy to determine whether a cell has XX or XY cLamosomes. The difficulty in he past has been to obtain cells from the unborn baby to examine.

Now it's done by amniocentesis, a technique developed to detect and treat Rh disease before birth, and now used to diagnose Down's syndrome and about 70 other genetic disorders. Amniocentesis can't be done until about the thirteenth week of pregnancy and requires inserting a needle into the uterus of the pregnant woman to withdraw fluid surrounding the unborn infant for testing. The fluid contains cells sloughed off from the baby.

Chinese scientists have developed a new method of obtaining fetal cells from the placenta by means of a cervical smear, almost as simple as a Pap test. So far it's only 80% to 90% accurate, compared to 99% for amniocentesis. But it can be done as early as seventh or eighth week of pregnancy, when a first trimester abortion is still a possibility.