Pregnancy can be one of the most challenging experiences of women. They experience changes in their body and add the need to stay healthy and to follow a strict diet for the health of the baby.

Researchers continued to explore the effects of pregnancy on women. Now, the latest findings suggest it could speed up the aging process.

A study, published in the journal Scientific Reports, shows that telomeres, the end caps of chromosomes that respond to age, become four months to four years older in women in every pregnancy.

Telomeres naturally shorten in all humans as we age. However, cigarette smoking, high body mass index and stress, which increases during pregnancy, could speed up the shortening process of these end caps, The Washington Post reported.

Changes in telomeres have been linked to cell death and increased risk of health conditions like cancer, cardiovascular disease and diabetes. In the study, researchers gathered more than 800 women in their early 20s in the Philippines.

The team analyzed their pregnancy and epigenetic age through DNA testing. Results showed that the more pregnancies a woman had, the “older” she appears biologically.

However, the researchers were surprised when the women who experienced faster aging after each pregnancy looked epigenetically “younger” while their baby was in the womb.

“Why would a woman look epigenetically younger during a pregnancy and epigenetically older after multiple pregnancies?” Calen Ryan, a biological anthropologist at Northwestern University, said. “Could it be that mom’s blood is getting contaminated with baby’s blood, or cells of baby’s blood, and if so is this an artifact of that? These are things we need to understand.”

Dan Eisenberg, one of the researchers and a biological anthropologist at the University of Washington, continued the study to further understand the pregnancy effects on aging process. He’s working with the same group of women and plans to analyze their telomere length before and after pregnancy.

Meanwhile, another team issued a research that supports the initial findings of Eisenberg’s team. The study, published in the journal Human Reproduction, analyzed the telomere length in nearly 2,000 American women, aged 20 to 44 years.

Researchers found that telomeres became 4.2 percent shorter in women who had live births compared to those who remained without children. The decrease led to 11 years faster cellular aging.

The pregnancy effects potentially led to shorter telomeres and faster aging due to stress. A study in 2016 found that indigenous women with children in Guatemala had longer telomeres despite giving birth.

But unlike other studied populations, the Guatemalan women receive more social support, which potentially reduced their stress levels during pregnancy. This then prevented their accelerated aging.

“In this indigenous Mayan society in Guatemala, children are seen as Godsends, as blessings,” Pablo Nepomnaschy, an epidemiologist at Simon Fraser University, said. “Women were expected, until recently, to have many children and in fact, there may be a lot of stress associated with not having children in that society.”