What’s the difference between gestational age and fetal (conceptional) age?

Gestational age describes how far along the pregnancy is and is tracked from the first day of your LMP. Fetal age, on the other hand, describes the actual age of the developing fetus and is tracked from the date of conception. 

Because conception typically happens during ovulation (about two weeks after your LMP), doctors usually only track gestational age, since the moment of conception can be very hard to pinpoint.