I had unprotected sex w/ my girlfriend last april 13 her menstrual cycle started btween april 18 to 21 (regular). Is there a high chance of pregnancy?

Pregnancy ? "Unprotected sex" on April 13, with a regular (expected) period on April 18 which ended in 4-6 days has minimal to no risk of associated pregnancy. If the bleeding is prolonged, however, obtain a serum HCG test to be certain, as some pregnancies can occur outside the womb (ectopic) and must be treated immediately. .