It's a girl," shouted Marcie Zanzig on hearing the happy tidings by phone from Chicago's Michael Reese Hospital and Medical Center. Though it sounded as if the excitement was over someone else's baby, she was actually talking about her own, unborn child. Scarcely nine weeks pregnant, Marcie, 27, had just learned the sex of her child. "It's like a birth announcement," she cried.

The possibility of such a remarkably early indication of sexual identity is due to a new medical test called chorionic villi sampling (CVS). Like amniocentesis, CVS retrieves genetic material so that it can be analyzed to determine whether a fetus might be afflicted by any of 350 or so genetic abnormalities, including Down syndrome. Both procedures also indicate the sex of the unborn, but amniocentesis cannot be performed until the 15th or 17th week of pregnancy. CVS can be done as early as the ninth week.

Marcie and Bob Zanzigs' early interest in the sex of their unborn child was more than mere curiosity. About a year and a half ago, they had learned that their firstborn son, Zachary, is a hemophiliac. While his blood disorder was of a type usually transmitted by the mother, hemophilia almost always affects only males. To their great relief, the Zanzigs now know that their next child is to be a daughter and thus spared the effects of the disease (though she might still be a carrier).

Earlier diagnosis through CVS offers the option of a first trimester abortion, should circumstances dictate. Such abortions, which can be performed in a clinic or a doctor's office, are simpler and medically safer than those done later in the pregnancy. "There is the advantage of privacy," adds Dr. Eugene Pergament, 52, the pioneer of the CVS technique in the U.S. "You can have the test, get the results, act on the information, and no one has to know what is going on." By contrast, second trimester abortions done after amniocentesis require full hospitalization. By then the mother is "already feeling the baby; she is emotionally invested in the pregnancy," says Dr. Norman Ginsberg, 39, an obstetrician who performs the CVS procedure at Michael Reese Hospital. "Women who terminate their pregnancy in the second trimester find it psychologically traumatic and physically difficult."

CVS was developed in the late 1960s by researchers in Scandinavia and was used tentatively in the Soviet Union and in China to determine the sex of the unborn before sophisticated genetic analysis was developed. British physicians eventually refined the process by using ultrasound to monitor the procedure accurately and thus decrease the chance of damage to the fetus. In turn, the technique was demonstrated to Drs. Pergament and Ginsberg at Michael Reese, which today is one of seven hospitals in the U.S. evaluating the safety and accuracy of the procedure for a National Institutes of Health study. So far, about 11,000 tests have been performed worldwide.

CVS testing is done nine to 11 weeks after a pregnant woman's last menstrual period. The obstetrician passes a catheter through the vagina and into the uterus to withdraw tissue samples from the chorion, which surrounds the amniotic fluid and developing fetus, which at this time is about one inch long. Since the chorion has the same genetic makeup as the fetus, the extracted tissue can be checked for genetic abnormalities. For the patient, the procedure itself usually takes only 15 minutes; no anesthetic is required, and the discomfort level is about that for a Pap smear. Lab results are available within days, as compared with the two to three weeks needed in amniocentesis (the standard procedure from the second trimester onward).

"No one to my knowledge has first declared a normal pregnancy on the basis of CVS and then had an abnormal baby born," says Pergament, a Yale graduate who holds a doctorate in genetics from Purdue and an M.D. from the University of Chicago. Still, he concedes, no test can be perfect. The process of analyzing the retrieved genetic material is basically the same, and, says Pergament, the results appear to be more than 99 percent accurate for both CVS and amniocentesis. Because of the enormous number of possibilities, some genetic flaws might not be identified in the highly specialized lab testing. Moreover, many birth defects, such as a cleft palate, are not detectable through CVS or amniocentesis.

Of even greater concern to doctors is the safety of CVS testing. "We've had 22 miscarriages in 1,000 pregnancies," says Pergament, based on the experience of Michael Reese Hospital so far. "But we think more than half those losses were not due to the CVS procedure." A little-appreciated medical fact, he adds, is that 20 percent of all pregnancies abort naturally, usually in the first three months: "There is no fetal heart beat, no growth, an empty sac, yet the chorion still sends signals to the mother's body as if she were pregnant." Overall, the miscarriage rate from CVS may be "a little bit higher" than from amniocentesis.

For many prospective mothers, especially those over 35, the benefits of CVS are clear. When Joyce Love, 40, a secretary-computer operator in Chicago and the mother of two (ages 19 and 21) became pregnant again, she chose CVS over amniocentesis, "because I don't think it's fair to the mother or baby to wait too long to find out if something is wrong." Besides, for Joyce, knowing as early as possible that her next child is a girl and genetically normal is part of the pleasure. "I want to make sure my baby has the right room color, put up draperies, new furniture, the works," she says. "There's so much I have to do."