TORONTO -- Doctors at Toronto's Hospital for Sick Children have invented a test on the tar-like first bowel movements of newborns for chemical clues that their mothers drank alcohol in pregnancy, a breakthrough in the detective work of diagnosing fetal alcohol syndrome.

For years, delivery-room doctors have plucked hair samples from squalling infants born to mothers suspected of drug addiction. But for the past several months, the laboratory at Sick Kids' Motherisk clinic has analyzed the black, sticky meconium that all newborn babies pass, a result of having digested amniotic fluid in the womb. They are looking for a chemical formed when alcohol bonds with fatty acids.

Like the notorious nausea drug thalidomide that caused babies to be born with disfigured limbs in the 1960s, alcohol is known as a teratogen, a substance that passes undiluted through the placenta from mother to child. Usually more damaging to a growing fetus than illicit street drugs such as crack cocaine, alcohol inflicts irreversible brain damage and is called the leading cause of mental retardation in the western world.

Until a few months ago, prenatal alcohol exposure was impossible to detect in a newborn, and children born to hard-drinking mothers who denied consuming alcohol during their pregnancies might be diagnosed years later, if at all, when symptoms of fetal alcohol syndrome (FAS) like impulsive behaviour and learning difficulties started to surface.

"The problem is not only the possibility of fetal alcohol syndrome, but also a situation where the baby goes home to a mother who is an alcoholic whose main purpose in life is to make sure she gets enough alcohol. So how can she care for that baby?" said Julia Klein, director of the Motherisk fetal toxicology laboratory, which developed the meconium test.

Over the past few months, the lab has analyzed meconium samples from more than 100 newborns whose mothers were suspected of drinking during their pregnancies. The test is most often requested by doctors and children's aid social workers.

In the lab, toxicologists measure levels of a substance called fatty acid ethyl esther or FAEE, a chemical compound of alcohol and fatty acids that becomes visible only after the first trimester of pregnancy and collects in the meconium as the fetus is exposed to more alcohol.

"Meconium is like a trash can," Dr. Klein said. "What the fetus experiences in utero accumulates there, and it stays there until the baby is born, so it's a very good medium for measuring what the fetus is exposed to."

Only trace amounts of the chemical are likely to be detected in the first bowel movement of a baby born to a woman who sipped an occasional glass of wine in pregnancy. But it will appear in abundance in the meconium of babies born to women who binged or drank regularly.

Not every woman who drinks when pregnant will give birth to a brain-damaged baby. Still, an estimated one in 500 children are born with FAS in Canada and the United States, though only those children whose mothers' drinking is confirmed can be diagnosed. At least 10 times as many are believed to have fetal alcohol effects -- the brain damage of the full-blown syndrome without its physical traits.

At St. Joseph's Health Centre in Toronto, doctors have requested meconium testing for babies born to women enrolled in the hospital's program for alcoholic expectant mothers as evidence to watchful child-protection workers that they remained sober during their pregnancies. "Our use has been more to advocate that the child is fine," said Peter Selby, a physician at the hospital. "But the test has to be carefully interpreted. It in and of itself does not make a diagnosis of FAS. All it says is alcohol was consumed."

Peggy Robertson, director of medical services at the Children's Aid Society of Toronto, said the agency has ordered the test in cases with a "high index of suspicion" of prenatal drinking, often involving poor women addicted to drugs with a history of tangling with the child-welfare system.

With a positive test, she said, "we monitor that much more carefully. It makes me get services in for that child even faster. Each intervention can make a huge difference."