During pregnancy you must have heard two words repeatedly and must have got confused about the difference – Gestational age and fetal age. You must be thinking that they are synonymous; when the reality is actually the other way around. According to the medical science, gestational age is what concerns the doctors more whereas you calculate the age of your child based on the fetal age. Although they are different but can be calculated easily with simple maths if you know at least one of them.

gestational age vs fetal age

What is Gestational Age?

It is the estimated age of your fetus which is calculated from the starting day of your final menstrual period. You must be wondering that how can the age of your fetus be calculated by the doctors when you have not conceived at that time? Doctors rely on the date of your last menstrual cycle as this date is a confirmed and reliable date although you may not have been pregnant that time.

This time is measured in weeks and technically speaking it includes approximately two weeks where you were not pregnant. The doctors examine whether the baby is perfect in weight, height, size of head and other details during pregnancy based on the gestational age.

What is Embryonic or Fetal Age?

It is the actual age of the baby and is counted from the date of conception, not from the first day of your last cycle. To understand the logic behind this technical aspect you need to know the science behind pregnancy. The appropriate time to conceive is the time during ovulation and this takes place usually in the mid of the menstrual cycle of 28 days that is 14 days after the ovulation. Thus technically fetal age is two weeks less than the exact gestational age. Doctors can easily calculate the two ages with simple maths as they have your first date of your last periods.

  • Gestational Age = Fetal age + 2 weeks
  • Fetal Age = Gestational age-2 weeks.

So if the gestational age is 8 weeks then fetal age is 6 weeks.

Why to Know these Ages?

It is really important to know the gestational and fetal age of the child as it help the doctors to chalk out the treatment of the child during the time of pregnancy, especially during any crisis. Only the knowledge of the two ages can help the doctors to determine that the development of the fetus is perfect.

The most important reason to know them is to find the due date of the delivery by applying Naegele’s rule to determine the baby’s age. According to the rule, the estimated due date (EDD) is based on Last menstrual Period (LMP) and so is basically related to gestational age. The calculation is:

  • EDD= LMP-3 months +1 year +7 days
  • Approximately EDD =LMP + 9 months

Moreover with the help of gestational age doctors can determine whether the movements of the baby are perfect or need any special care.