Trying to Conceive: Gestational vs. Fetal Age
Gestational age refers to the length of time since the first day of your last period. So, when the doctor says your gestational age is four weeks, it just means that it's been four weeks since your last period started. (So, with this method of dating a pregnancy it means you're technically two weeks pregnant before you even conceive.)Your healthcare provider may also refer to you as four weeks LMP (last menstrual period). It means the same thing when youre trying to conceive.
Fetal age refers to the age of your developing baby, counting from the estimated date of conception. The fetal age is usually two weeks less than the gestational age. This is one of the reasons why your doctor or midwife will pay particular attention to the date calculations on any ultrasounds you may have as well as the fundal measurements (measurements of the height of your uterus) that are done at your regular prenatal checkups. It's all a way of cross-checking the accuracy of your due date and ensuring that your baby's development is pretty much on track.
A normal pregnancy lasts from 38 to 42 weeks. Babies born before 37 weeks gestational age are considered premature, so it's important to know both the gestational age and the baby's estimated weight if you go into premature labor.