The preterm birth rate in South Korea is on the rise, while the country's overall birthrate reached an all-time low, data showed on Sunday.

Statistics from the Korea Institute for Health and Social Affairs showed that the total number of births in the nation has decreased over the past decade, shrinking from 471,000 in 2011 to 261,000 in 2021.

During the same period, the rate of premature births have increased. The rate of preterm births grew from 6 percent to 9.2 percent and the rate of infants born with a low birth weight increased from 5.2 percent to 7.2 percent.

Premature babies are born before their bodies and organ systems have fully developed. Typically, babies born before 37 weeks of pregnancy are considered premature. Low birthweight refers to babies born weighing less than 2.5 kilograms.

Recent studies have suggested premature births are related to infertility treatments, such as in vitro fertilization treatment or artificial insemination. In recent years, twins and higher-order multiples – also known as multiple births, in which the mother gives birth to two or more babies -- have increased largely due to fertility treatments. However, it is estimated that more than half of all twins are born prematurely, and the risk of premature delivery increases with triplets and other multiple births.

Statistics showed that the number of twins and multiple births slightly increased from 139,000 in 2011 to 140,000 in 2021 amid a steep decline in total number of births. Among multiple births in 2021, 66.6 percent were premature and 59.9 percent were born with a low birthweight, with some overlap between the two.

“Premature babies are more likely to have health risks in terms of lung function and blood pressure. Their developmental status, diseases and disabilities should be continuously monitored by the government,” said Choi Eun-jin, a research fellow at the Korea Institute for Health and Social Affairs.