Is it true that if your baby has a big head, a natural vaginal delivery is not possible?

Like Jorelle mentioned, it differs from each woman. I have a friend who's really petite and small but she managed to pop out her 4kg baby daughter via norma delivery. Another friend who's an average Singaporean built who had to do emergency C-Sec even though her baby was about 3.4kg (she didn't dilate fast enough). Keep an open mindset - your gynae would be able to advise you better based on your scans to see baby's growth.