Multiple births double in Korea while rates fall in US, Japan

Multiple pregnancies, considered a high-risk factor in childbirth, have been declining in the United States and Japan over the past two decades, but they have significantly increased in Korea.

Multiple pregnancy refers to carrying twins or more.

The Korean Society for Maternal Fetal Medicine (KSMFM) and the Korean Society for Assisted Reproduction (KOSAR) highlighted this reality at the “13th Korean Society for Maternal-Fetal Medicine Research Symposium” held last Saturday at the Seoul National University Medical Library. They subsequently released a joint fact sheet on Thursday that summarized the risks of multiple pregnancies.

The societies emphasized that multiple pregnancies in Korea are rapidly increasing as more couples attempt in vitro fertilization due to rising marriage and childbearing ages. They stressed that awareness of the risks is necessary, as this increase places a burden on the health of both mothers and newborns.

In Korea, this trend is especially pronounced: the rate of multiple births remains exceptionally high globally. The proportion of multiple births among all births more than doubled over 17 years, rising from 2.7 percent in 2007 to 5.5 percent in 2023. In contrast, the same period saw decreases in the United States (from 3.37 percent to 3.14 percent) and Japan (from 2.21 percent to 2.04 percent).

The increase in multiple pregnancies in Korea is closely linked to the rise in assisted reproductive technologies (ART), such as in vitro fertilization (IVF). The societies emphasized that multiple pregnancies are a significant high-risk factor in obstetrics. The probability of twin births in natural conception is around 1 percent, but rises to 25–30 percent with IVF procedures.

According to the fact sheet, twin pregnancies carry much higher risks of complications compared with singleton pregnancies. There is a sixfold higher risk of preterm birth and labor. The risk of preeclampsia is more than double; for triplets, it is nine times higher. The risk of postpartum hemorrhage is about three times higher, as is the risk of thrombotic disorders.

Experts note that multiple births also entail greater challenges during pregnancy and delivery, along with substantially higher postpartum childcare stress and financial burdens. These risks extend to fetuses and newborns: over half of twins are born before 37 weeks, and 90 percent of triplets are either preterm or low birth weight. About 25 percent of twins and 75 percent of triplets are admitted to the neonatal intensive care unit (NICU). Twins face a risk of cerebral palsy that is four times higher, and triplets have a risk that is 18 times higher compared to singletons.

Both societies said the goal of a healthy pregnancy is safety for the mother and baby. Advances in embryo culture and freezing have raised pregnancy success rates, and fertility treatments are shifting toward minimizing multiple pregnancies. Single Embryo Transfer (SET) helps reduce the likelihood of twin pregnancies while maintaining pregnancy success rates.

They added that clinicians should carefully determine the number of embryos transferred during IVF, considering the mother’s age, embryo quality, previous pregnancy history, and acceptance of twin pregnancy. If clinicians diagnose a multiple pregnancy, high-risk specialists must provide regular check-ups and intensive management.

“While transferring two to three embryos based on maternal age is sometimes done to increase pregnancy success rates, the ultimate goal of assisted reproductive technology goes beyond simple pregnancy success to the birth of a healthy singleton infant,” KOSAR President Suh Chang-suk said. “Advancements in embryo freezing and culture techniques, preimplantation genetic diagnosis, and improved embryo selection algorithms further support single embryo transfer. Evidence shows that SET maintains cumulative pregnancy rates while preventing unnecessary multiple pregnancies.”

KSMFM President Park Joong-shin added, “Because multiple pregnancies are a significantly high-risk factor associated with preterm birth, developmental delays, cerebral palsy and other complications, a preventive approach is crucial. We hope this fact sheet helps those preparing for pregnancy or considering infertility treatment.”