Researchers found that of 330 children they followed to age 5, the half who were exposed to meth in the womb tended to have more behavioral issues, sadness and anxiety.

The findings, reported in the journal Pediatrics, do not point to "huge" differences between meth-exposed kids and their peers.

But the results are still "worrisome," said lead researcher Linda L. LaGasse, of Brown University and Women & Infants Hospital in Providence, Rhode Island.

Methamphetamine is a highly addictive stimulant that can be snorted, smoked, injected or swallowed. Government figures suggest that more than 10 million Americans, or about four percent of the population, have used the drug.

Unlike other illegal drugs, meth seems to have a greater appeal to women than men. In the U.S., pregnant women account for about seven percent of people who seek treatment for meth abuse.

"Meth exposure is a huge problem," LaGasse said.

But this study, she told Reuters Health, is the first to follow meth-exposed newborns over time and chart their behavioral and emotional well-being.

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The study included 166 U.S. children whose mothers had abused methamphetamine during pregnancy, and 164 kids who hadn't been exposed to the drug. Both groups were similar as far as race, birthweight and mothers' education, and most were on Medicaid, the government insurance program for the poor.

When the children were three and five years old, their mothers went through standardized interviews about any behavioral or emotional issues their child was having.

On average, the study found, the meth-exposed children scored a few points higher on "externalizing" symptoms -- like aggression and inattention -- at the age of five.

The difference, LaGasse said, owed to the fact that children who weren't exposed to meth showed a decline in externalizing problems between the ages of three and five -- a natural result of maturing.

On the other hand, kids who were exposed to meth showed no such improvement overall.

Then there were the "internalizing" symptoms -- things like sadness, anxiety and withdrawn behavior. Children exposed to meth tended to have more of those at both ages, the study found.

The scores from these interviews can't be used to diagnose any clinical disorders, like depression or attention-deficit hyperactivity disorder (ADHD), LaGasse stressed.

But they point to kids who may be on a "trajectory" toward longer-term problems, she said.

According to LaGasse, the internalizing symptoms may be particularly concerning because they are more likely to go undetected.

"These are not disruptive kids," she noted, "They may not get noticed."

The results do not prove that prenatal meth exposure, itself, is responsible for the higher rate of behavioral and emotional symptoms. "We can't say that for sure," LaGasse said. But, she added, her team did control for a wide range of other factors, including mothers' own mental health.

Behavior problems were more common in kids whose mothers had psychological symptoms, the researchers found -- but that didn't explain away the connection to meth exposure.

LaGasse said that parents who think their children are having behavioral or emotional problems can seek help. If they are on Medicaid, they can ask if their state has programs in place. Or they can ask their pediatrician, she said.

It's not clear how methamphetamine affects the developing fetal brain, LaGasse said.

But like cocaine, meth does seem to constrict blood vessels supplying the placenta, which can lessen the amount of oxygen reaching the fetus.

Back in the 1990s, early studies of "crack babies" brought up concerns that the crack cocaine problem would result in a generation of severely brain-damaged kids. Since then, research has shown that while crack-exposed kids may have more behavioral problems and developmental delays, they have fairly subtle differences from their peers.

SOURCE: Pediatrics, online March 19, 2012.

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