Question

How can a doctor tell how old a baby is while it's still in the whom?

Answer 1

Fetuses have specific milestones based on their age in the womb. There's a chart in this link.

https://www.ck12.org/biology/pregnancy/lesson/Pregnancy-and-Childbirth-MS-LS/

A doctor/nurse can take an ultrasound of the womb to see what the fetus looks like. Then, they can see what physical features it has and judge based on the expected growth of a typical fetus.

Answer 2

https://kidshealth.org/en/parents/birth-defects.html