This terminology does vary geographically and over time, and it may need clarification if not explicitly defined in relevant articles.
For example, mothers with uncontrolled diabetes (Type 1, Type 2, or Gestational) cook very large babies.
When a baby is small, it might be due to a placenta that’s not working like it should.
If you were having regular periods before pregnancy, your doctor will calculate your due date based off of your last menstrual period.
This goes back to the fact that in order to get pregnant, your body ovulated—or released an egg—roughly in the middle of your cycle and it was fertilized by sperm. By the time most women miss a period and find out they’re pregnant, the baby has been growing for 2 weeks, but the mother is actually 4 weeks along because the gestational period starts with the first day of your last period.
I remember because I ended up in the hospital shortly after. :( ok how it works: I'll use me as an example, I am 10 weeks pregnant on July 16 (tomorrow) I was inseminated on May 22 (8 weeks ago) but yet my period started on May 7 (10 weeks ago).