There is a gestational age N then there is a
fetal age. The gestational is where your baby is still an egg waiting to implant. The
fetal age is how old the baby might just be, which could be more accurate from an ultra sound but the baby wont show until about ten Weeks. Doctors always go by your last menstrual period, this is just an estimate since there Is not a way to tell exactly when your baby implanted and started developing.