The educational health content on What To Expect is reviewed by our team Pregnant sex freak experts to be up-to-date and in line with the latest evidence-based medical information and accepted health guidelines, including Pregnant sex freak medically reviewed What to Expect books by Heidi Murkoff. Wait until you have one during pregnancy! The only way to know for sure is to take a pregnancy test. Sex can be a lot messier. There are many reasons your period could be late—even if your cycle is usually regular.