The study examines the relationship between reproductive history and biological aging in young adults from the Cebu Longitudinal Health and Nutrition Survey in the Philippines. Using six epigenetic clocks, the researchers found that pregnancy was associated with accelerated biological aging in women, both cross-sectionally and longitudinally. Specifically, women who had been pregnant exhibited faster aging across all six measures of biological aging. Longitudinal increases in pregnancy number were linked to accelerated aging in two epigenetic clocks. In contrast, the number of pregnancies fathered by men was not associated with biological aging. These findings support the hypothesis that pregnancy accelerates biological aging, even in young women, and suggest that these effects can be detected in a high-fertility context. The study also controlled for various social, environmental, and genetic confounders, providing robust evidence for the tradeoff between reproduction and aging.The study examines the relationship between reproductive history and biological aging in young adults from the Cebu Longitudinal Health and Nutrition Survey in the Philippines. Using six epigenetic clocks, the researchers found that pregnancy was associated with accelerated biological aging in women, both cross-sectionally and longitudinally. Specifically, women who had been pregnant exhibited faster aging across all six measures of biological aging. Longitudinal increases in pregnancy number were linked to accelerated aging in two epigenetic clocks. In contrast, the number of pregnancies fathered by men was not associated with biological aging. These findings support the hypothesis that pregnancy accelerates biological aging, even in young women, and suggest that these effects can be detected in a high-fertility context. The study also controlled for various social, environmental, and genetic confounders, providing robust evidence for the tradeoff between reproduction and aging.