Gestation is the period when a fetus develops inside a mother's uterus, typically lasting about 40 weeks or 280 days for humans.
Gestation begins when a sperm fertilizes an egg, creating a zygote. This single cell divides repeatedly as it travels through the fallopian tube and implants in the uterine wall. The developing embryo then grows into a fetus, undergoing critical stages of organ and system formation.
The three primary stages of gestation are:
Most gestations last between 37 and 42 weeks. A full-term pregnancy is 37-40 weeks, while preterm births occur before 37 weeks. Post-term pregnancies extend beyond 42 weeks. According to the American College of Obstetricians and Gynecologists, only about 4% of babies are born on their due date.
Many people confuse gestation with other pregnancy-related terms. For example, gestation is not the same as the menstrual cycle, which averages 28 days but varies widely among individuals., gestation differs from labor, which is the process of childbirth itself.
Another misconception is that all pregnancies last exactly 40 weeks. In reality, due dates are calculated from the first day of the last menstrual period (LMP), not from conception. This method adds about two weeks to the actual gestational age, as ovulation typically occurs around day 14 of the cycle.
| Term | Definition | Duration |
|---|---|---|
| Gestation | Time | ~40 weeks |
| Trimesters | Three stages of pregnancy | Each ~13-14 weeks |
| Due Date | Estimated delivery date | Calculated from LMP |