University of California - San Francisco Jan 21 2025 UCSF researchers discovered a molecular timer that gets activated in the first days of pregnancy and influences when mice give birth. A typical human pregnancy lasts 40 weeks, but most parents know this number is only a rough estimate. Babies are born on a seemingly unpredictable timeline, with a normal pregnancy ranging from 38 to 42 weeks. And 10 percent of all births are preterm, meaning they occur before 37 weeks of gestation, which puts