Do girls always bleed the first time they have sex?

Hi, and thanks for your medical question on eHealth forum!

If this was your girlfriends second time—which means she had proper intercourse just once before, then it is possible that her hymen did not rupture then, and it ruptured now.

However, if she bleeds every time you have sex, then this needs to be investigated. The various causes for vaginal bleeding after sex are injury and friction, STDs like Chlamydia, gonorrhea, and trichomoniasis, cervical polyps, yeast infections, non specific vaginitis, endometriosis, cervical dysplasia which is a precancerous condition, uterine polyps, uterine fibroids and cervicitis. None of them are conditions that should be ignored.

Since a confirmed diagnosis cannot be given on net please discuss these possibilities with your gynecologist once and get the required tests like internal examination, PAP smear, vaginal swab test for STD, and ultrasound. Hope this helps. Take care!