Abortion rates declined significantly among Texas girls – though some got riskier abortions later in pregnancy – after the state enacted a parental notification law, researchers say.

The findings could have a strong influence on the abortion debate. Texas is the biggest of 35 states that require minors to notify their parents or get their consent before obtaining an abortion, although a judge can usually grant a waiver.

Researchers at Baruch College at City University of New York studied the records of teen abortions and births for the two years before the Texas law took effect on Jan. 1, 2000, and for three years afterward.

Abortion rates dropped for girls ages 15 through 18, even though the 18-year-olds were not subject to the law. But the drop was more pronounced among the younger girls. Their rates fell 11 percent to 20 percent more than the rate among the 18-year-olds did.

“The law has definite behavioral effects,” said lead researcher Ted Joyce, a Baruch professor of economics.

The study was reported in today’s New England Journal of Medicine.

In the study, birth rates declined for all ages in the 15- to 18-year-old group. At the same time, the abortion rate among 18-year-olds fell from 27.7 abortions per 1,000 girls before the law to 25.8 afterward. The rate dropped from 18.7 to 14.5 among 17-year-olds; 12.1 to 9.0 among 16-year-olds; and 6.5 to 5.4 among 15-year-olds.

Texas state Sen. Florence Shapiro, who sponsored the notification law, said the findings show that more parents are becoming involved in their daughters’ “life-altering decisions.”

“That was my intent,” she said. Last year, Texas went further and enacted a law requiring parental consent.

In the study, girls 17 1/2 or slightly older were one-third more likely to have an abortion in the second trimester than girls already 18 when they became pregnant, indicating many waited until they turned 18 to escape the notification requirement.

Abortion later in pregnancy carries a much higher rate of deadly complications, though the overall risk is still extremely small.

The study “draws attention to the way that these kinds of laws can put teens in a compromised position that puts their health at risk,” said Lawrence Finer, director of domestic research at the Guttmacher Institute, a nonprofit research group that specializes in reproductive issues.

The abortion rate has been falling among all girls since 1991 both nationally and in Texas, as have teen birth rates, for reasons that are believed to include greater use of birth control, more effective methods and a delay in first-time intercourse.