But at the same time, activists said the report proves modern medicine has been used for long-held prejudices.
A study released Monday in Britain's leading medical journal, the Lancet, said aborting female fetuses is common because of a preference for boys in India, where a bride's family traditionally gives cash and gifts to her husband's relatives.
Indian census figures appear to back the study. From 1991 to 2001, the number of girls per 1,000 boys declined from 945 to 927 in the country of over a billion people.
Ultrasound technology, used to check fetal health, can also check gender and has become more common in India, though the country has outlawed prenatal gender checks since 1994.
Dr. Narendra Saini, spokesman for the Indian Medical Association — which says it represents about 178,000 doctors — insisted such checks have waned since the Supreme Court ordered a crackdown in 2001.
"This is not happening for the past four or five years after strict laws were put in place," Saini said.
The study's authors "are mixing the present with the past," he said. "Yes, it happened at one time. Now it doesn't."
India's government did not immediately comment on the report.
The report said researchers analyzed data from an Indian national survey on 133,738 births, concluding that about 500,000 female fetuses were aborted each year in the two decades, since ultrasound became widespread.
"A figure of 10 million missing female births would not be unreasonable," it said.
It also said the deficit of girls born as second children was more than twice as great among educated mothers than among illiterate ones.
Activists said the study helped prove that Indian couples still abort unwanted female fetuses. They blamed poor law enforcement.
"Not even one person has been booked so far. That shows how lax the system is," said Ranjana Kumari of the Center for Social Research. "There is connivance between the doctors and the parents who don't want girl children. The government has to come forward on a war footing to put an end to this practice."
Madhu Gupta, a leading gynecologist in the country's most populous state, Uttar Pradesh, agreed that couples still abort female fetuses, but insisted the practice has diminished.
"Its rate has definitely come down. Small-time doctors do it, but there is drastic reduction," Gupta said in the state capital, Lucknow. "But the 500,000 figure is just too big. It is totally fictitious. It is just not possible."