Abortion rates in the developed world have dropped dramatically to a record low during the past 25 years, but only fallen slightly in poorer developing nations, a new global study said.

The study conducted by the World Health Organization and the Guttmacher Institute, a U.S.-based non-profit organization promoting sexual and reproductive health, also found that restricting or legally banning access to abortions did little to lower the rates, and instead is more likely to force people to turn to clandestine and unsafe measures.

The researchers looked at total numbers of each year between 1990 and 1994 and between 2010 and 2014, finding that an average of 56.3 million abortions took place each year worldwide during the 2010-2014 period, a 10-percent increase compared with the 1990-1994 period. But researchers mainly attributed it to population growth.

During the past 25 years, the study said, the developed countries' annual abortion rate per 1,000 women of childbearing age (15-44 years old) dropped from 46 to 27. However in poorer countries, the abortion rate remained virtually unchanged, dropping from 39 to 37.

Published in The Lancet medical journal on Wednesday, the study highlighted the shortage of access to modern contraception methods in developing countries to reduce unwanted pregnancies.

"In developing countries ... family planning services do not seem to be keeping up with the increasing desire for smaller families," leading researcher Gilda Sedgh said.

By contrast, she explained, the downward trend of abortion rates in wealthier countries is largely due to increased use of modern contraception that allows women to control the timing and number of children they want.

According to the study, Eastern Europe has seen the biggest decline in abortion rates in the past 25 years as the annual average abortions there dropped from 88 to 42 per 1,000 women.