Healthcare providers describe the age of a fetus in two ways. The first is based on the number of weeks since the first day of the woman’s last menstrual period. This is referred to as gestational age. The second way to describe the age of a fetus is based on the number of weeks since the time of conception. This is referred to as conceptional age. For the information presented here, gestational age, or weeks since the first day of the last period, will be used.
9 Months in the Womb
Embryo or Fetus Age Determination
Stages of Pregnancy
Healthcare providers call an unborn child either an embryo or a fetus depending on the age. When a pregnancy is ten weeks’ gestation or less, they describe it as an embryo. When the age is more than ten weeks’ gestation, they use the term fetus.
Trimesters
A normal, full-term pregnancy is 40 weeks.
It’s divided into three trimesters. Each trimester lasts between 12 and 14 weeks, or about three months.