To estimate how far along you are pregnant, this app is referred to the gestational age. After all, it is the common reference point used by health care providers. For purposes of consistency, the first day of the last menstrual period (LMP) is the standard from which they start counting.

You may have heard of a less familiar term known as fertilization age, which is basically the embryonic age of the baby. Because the gestational age starts from your LMP, you are technically not pregnant until two weeks after that when you have ovulated.

Since the first two weeks of pregnancy involves menstruation, ovulation and preparing your uterus for pregnancy, your baby is still an idea at this point. So when you will be 16 weeks pregnant, your baby technically will be 14 weeks old.