Testing Fetuses

A checkup in the womb

Is the unborn baby healthy, or does a defect destine it to an early death or a life of debilitating illness? In many cases the answers to these worrisome questions can be found in laboratory analysis of a small sample of the amniotic fluid drawn from the sac surrounding the baby in the womb. Using amniocentesis, as the technique is called, doctors can accurately predict serious disorders like Down's syndrome (mongolism) and Gaucher's disease (a metabolic disorder); faced with a grim certainty, prospective parents can opt for abortion. But amniocentesis has its limitations; it cannot foretell all defects. Now comes fetoscopy, a technique that takes over where amniocentesis leaves off by allowing direct examination of the fetus.

Using fetoscopy, physicians can actually see the fetus in the uterus and spot certain physical defects. Says Dr. Thomas Gindhart, of the National Cancer Institute: "You can look right at parts of the fetus as it floats by. You can count the number of fingers." That alone can reveal much about the condition of the fetus. A six-fingered hand, for example, may accompany some forms of retardation. Also discernible are such features as eyes, ears, mouth and genitals. Even more important, the technique enables doctors to take blood and tissue from the fetus. From these samples they can diagnose a severe skin disease known as epidermolytic hyperkeratosis and such blood disorders as hemophilia and thalassemia, and the 40% of sickle cell anemia cases that amniocentesis misses.

The exceptionally delicate procedure, performed some 15 to 20 weeks into the pregnancy, is done under a local anesthetic. Doctors scan the woman with pulsed sound waves to locate the fetus, the umbilical cord and the placenta. After making a small incision in the abdomen, they insert into the uterus and the amniotic sac a pencil-lead-thin tube containing an endoscope with fiber-optic bundles that transmit light. This enables the physicians to see tiny areas of the fetus. By inserting biopsy forceps into the tube, doctors can take a 1-mm (.04 in.) skin sample from the fetus. They prefer to excise it from the head, where there are no major blood vessels or nerves and the skull provides a firm surface for their work. To draw a blood sample, the doctor inserts a needle through the tube and punctures one of the fetal blood vessels lying on the surface of the placenta. Says Dr. Mitchell Golbus, a fetoscopy expert and director of the prenatal detection program at the University of California at San Francisco: "It has to be done with a great deal of care and skill because we want the pregnancy to continue unharmed if the test comes back normal."

At the Yale-New Haven Hospital, doctors have been performing fetoscopies on women who fear (usually because of family histories) that their children will be defective. In many cases the test can reassure patients that their babies will be normal. Says Yale Obstetrician John Hobbins, who with Maurice Mahoney, a pediatrician and geneticist, pioneered fetoscopy: "Its benefit is that we can salvage 75% of the fetuses that would otherwise be aborted." But Hobbins and other doctors stress that the technique is still highly experimental. It induces miscarriage in about 5% of the cases (the rate for amniocentesis is less than 1%), and has been tried on only a few hundred women, most of them at Yale and the University of California at San Francisco.

Though the disorders that fetoscopy now helps diagnose are few, and quite rare, researchers expect to use it eventually to detect such maladies as albinism (lack of pigment) and muscular dystrophy. Refinements in blood analysis may also make it possible to discern in the fetus levels of any toxic substances the mother has been exposed to. Some doctors foresee a more startling prospect: using fetoscopy to administer medicine directly to fetuses and perhaps even perform minor surgery on them while they are still in the womb.

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