Don't be alarmed if naps are suddenly part of the daily routine. "Fatigue is very common, especially in the first trimester -- again due to increased hormone levels, as well as the demand placed on a woman's body during this critical time of fetal development," explained certified nurse-midwife Regis by e-mail [source: Regis].
The body is working overtime as it ramps up progesterone levels and prepares a healthy, safe home for your baby's next 40 weeks. This blanket of tiredness usually lifts around the second trimester. But remember that every pregnancy is different, so if you're tired throughout the entire process, you can always point to the intense physical effort required to make a human.