A new analysis of births in India finds that about 10 million female fetuses may have been aborted over the past two decades. Sexual selection is illegal in India, but the practice continues anyway.

Fewer girls than boys are born in India. A study published in the journal Lancet says the cause is undoubtedly prenatal sex determination using ultrasound technology, followed by abortion of female fetuses.

According to investigators at the Postgraduate Institute of Medical Education and Research in Chandigarh, India and the University of Toronto in Canada, the 2001 Indian census shows only 927 girls age six and under for every 1,000 boys that age. This is a drop from 962 girls for every thousand boys since the 1981 census.

"The gap in missing females is not a problem in some parts of India," said University of Toronto researcher Prabhat Jha, who attributes the birth gender gap to the cultural preference for boys in India. It's a problem in all parts of India." He says the gap is most noticeable among second and third children in a family if the first born is a girl.

"If the first child is a boy, then the second child is almost equally likely to be a boy or a girl, which is exactly what you would expect," continues Jha. "But if the first child is a girl, then you see a 30-percent deficit in second females. Particularly if the first two children are females, then you see even a larger deficit in the third female."

Mr. Jha's team says the reason the Indian birth gender gap has widened since 1981 is the increasing use of ultrasound, a technology that produces a shadowy picture of a fetus and can help determine its sex.

The researchers say gender selection is practiced equally among all religious groups in India. But it is more common in urban than in rural areas and more widespread among the educated than illiterates. They suggest that educated people in cities have more access to ultrasound clinics.

Fetal sex determination and abortion based on gender have been illegal in India since 1994. But Mr. Jha says the law is not vigorously enforced and is easy to circumvent.

"Ultrasound clinics can indirectly reveal the sex of the child without explicitly doing so and, hence, be in clear violation of the law," he said. "There is not enough enforcement of certain clinics or cracking down on some of the more flagrant operators that are going around advertising sex selection very explicitly."

In a commentary accompanying the Lancet study, obstetrician Shirish Sheth of Breach Candy Hospital in Mumbai writes that the only answer to this practice is respecting women's sexual, reproductive, and human rights. But Dr. Sheth adds that to eliminate prenatal sex selection and consequent termination of life is a huge task.