The New York-based Guttmacher Institute's research found that abortions are more than 22 times more common than the government's estimate of less than 700,000 terminations, produced by focusing on state-run hospitals and clinics.
Just over 80 percent of abortions took place using drugs like mifepristone and misoprostol, 14 percent were performed surgically in clinics and hospitals, and 5 percent were conducted using other, typically unsafe, methods.
"Women in India face considerable challenges trying to obtain abortion care, including the limited availability of abortion services in public health facilities," the Guttmacher Institute's investigator Susheela Singh, said in a statement.
"Our findings suggest that a shortage of trained staff and inadequate supplies and equipment are the primary reasons many public facilities don't provide abortion care," she said of the study, published in the Lancet Global Health journal.
It is India's first national study of the incidence of abortion and unintended pregnancy, researchers said.
Half of India's more than 48 million pregnancies were unintended, and a third resulted in abortions, the study said, using 2015 abortion pill sales and distribution data and surveys of six highly populated states.
In addition, the public sector - the main source of health care for rural and poor women - accounted for only a quarter of abortions, partly because many state-run hospitals and clinics do not offer abortion services.
"Although abortion has been legal under a broad range of criteria in India since 1971, we have never had a reliable estimate of the number occurring until now," said Chander Shekhar from the Mumbai-based International Institute for Population Sciences, which collaborated on the study.
"This new evidence provides policymakers with information that is essential for designing and implementing effective reproductive health care programs," he added in a statement.
(Reporting by Nita Bhalla @nitabhalla, Editing by Katy Migiro. Please credit the Thomson Reuters Foundation, the charitable arm of Thomson Reuters, that covers humanitarian news, women's rights, trafficking, property rights, climate change and resilience. Visit http://news.trust.org)
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