Youngentob is lead author of two studies detailing these findings in the December issue of Behavioral Neuroscience.

Even more than family history, fetal exposure to alcohol will predict if a person abuses alcohol later in life. And, the earlier that first experience, the higher the probability the person will have problems with this substance into adulthood, experts say.

Full-blown fetal alcohol syndrome involves profound mental retardation as well as cranial facial defects. But there are also more subtle effects of being exposed to alcohol in utero.

The senses are among earliest systems to develop and seem to allow the developing fetus to "learn" from the mother what is OK to eat and drink by virtue of what mom ingests during pregnancy, Youngentob explained.

"All that information gets transmitted to the fetus during gestation or the infant during lactation," he said. "It turns out that this adaptive mechanism is to the advantage of the organism and probably works for humans as well."

Unless it involves a substance of abuse, he added.

The new studies tested the hypothesis that exposure to alcohol while in the uterus resulted in an altered sensory response to the substance that then affected later behavior.

"The hypothesis was that there are these neuroadaptive changes that essentially make the ethanol [alcohol] smell and taste better to the animal. So, the animal, because of the fetal exposure, has 'learned' that ethanol is something that's good to eat," Youngentob said.

For the first study, rats that had been exposed to alcohol in the womb via maternal consumption were more likely to choose alcohol versus a nonalcoholic substance as young rats but not as adults.

The second study followed a similar protocol: Rats were exposed to alcohol while still in the uterus.

Compared to rats whose mothers just ate chow, the prenatally exposed rats sniffed alcohol more. They also had an altered odor response in their nasal passages.

"We know that the fetus has smell sensations developing in utero, and this is almost a need for survival, because you see with animals when they're born, they immediately know where to gravitate for maternal milk. The same thing [happens] when you place a baby on the mother's chest, he will recognize where the breast is just by smell," noted Dr. Raul Artal, professor and chair of the department of obstetrics, gynecology and women's health at St. Louis University.

"Learning different smells in utero and becoming familiar may be something that has a role in developing smell and taste for alcohol. This is almost a primitive type of response. It has nothing to do with intelligence. It's just part of life preservation."

In both cases, if the young rat had no more experience with alcohol by adulthood, the alcohol lost its attraction.

"The good news is that in the absence of a substance being biologically relevant -- that is, not being exposed to it -- then the animal becomes biologically neutral again," Youngentob said. "If the animals only get that fetal exposure, and you test them as adults, it's gone in terms of neurophysiological response."

But, if humans get adolescent exposure to alcohol, it can perpetuate the cycle, he said.

Youngentob and his colleagues are testing whether adolescent exposure to alcohol perpetuates the cycle in humans.

The clear message: Don't drink when pregnant, and keep alcohol away from teenagers, the researcher said.

More information

There's more on fetal alcohol syndrome at the U.S. Centers for Disease Control and Prevention.