Gestational Age

Gestational age is the number of weeks the pregnancy lasts or the age of the pregnancy. In other words, it is the number of weeks a baby has been in the uterus. It can also be termed as AOG and is calculated with the women’s last menstrual period and cycle length. Use this calculator, to find your gestational age.

Last menstrual period
Cycle Length
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Estimated Date of Delivery
Gestational age

The actual date of conception generally isn’t known for humans, so gestational age is the common way to measure how far along a pregnancy is. Where your baby is in their development — such as whether their fingers and toes have formed — is tied to gestational age.

Gestational age is measured in weeks from the first day of your last menstrual period. This means that your last period counts as part of your pregnancy. Even though you weren’t actually pregnant, your period is a signal that your body is preparing for pregnancy.

Fetal growth doesn’t actually start until conception, which is when sperm fertilizes an egg.

Your doctor can also determine gestational age using ultrasound or after delivery.

During an ultrasound, your doctor will measure your baby’s head and your abdomen to determine gestational age.

After birth, gestational age is determined using the Ballard Scale, which assesses the physical maturity of your baby.

Gestational age is divided into two periods: embryonic and fetal. The embryonic period is week 5 of pregnancy — which is when the embryo implants in your uterus — to week 10. The fetal period is week 10 to birth.


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