ATLANTA (AP) - So many new mothers lie when asked whether they drank alcohol during pregnancy that some national statistics on birth defects should be thrown out, a government study says.

Only about one in 20 women who drink during pregnancy admits it on her child's birth certificate, according to a study presented Tuesday.

In most states, women are asked after delivery whether they smoked or drank alcohol during pregnancy. Their answers are listed on birth certificates along with records of birth defects.

But many new mothers lie about their drinking or answer no because they think they haven't consumed enough alcohol to hurt the child, said Marc Weisskopf, a Centers for Disease Control and Prevention epidemiologist.

His study compared what women said for birth certificates and what they said in a telephone survey several years later. Just seven of 278 women admitted alcohol use on the birth certificate; 32 admitted it in the telephone survey.

The study projected the number of women who actually drank during pregnancy was 131 - nearly 20 times the number who admitted it on birth certificates.

The study urged the government to stop using alcohol data from birth certificates until accuracy can be improved. In 1999, 1 percent of women reported consuming alcohol during pregnancy.

The National Center for Health Statistics uses birth certificate data to pinpoint nationwide trends on pregnant women's alcohol use.

Exposure to alcohol in the womb can stunt growth, harm a baby's memory and contribute to learning problems.

``One would like to be able to look at alcohol use during pregnancy and ask: Is it higher than we'd like?'' Weisskopf said. ``The problem is, can you trust the data?''

Medical experts have long known that some women, embarrassed by the stigma associated with drinking while pregnant, lie about or underestimate the alcohol they consume.

The data have become so flawed that NCHS plans to eliminate the alcohol question from the standard birth certificate it suggests to states. The change is expected to be made by 2003, a spokeswoman said.

Weisskopf's study surveyed women in Illinois, Michigan, Indiana, Ohio and Wisconsin between 1989 and 1995.

The survey also found birth-certificate data underestimate tobacco use by 20 percent, a figure roughly in line with what other studies have found.

Copyright 2001 The Associated Press. All rights reserved.