Pregnancy is possible whenever semen enters the vagina. Generally, performing oral sex on a penis does not carry a risk for pregnancy because semen does not enter the vagina. To be clear, semen in the mouth cannot cause pregnancy; in order for pregnancy to occur, the semen would have to enter the vagina (whether on the penis, hands, or another body part).
While oral sex doesn’t carry a risk for pregnancy, some STIs can transmit through oral sex. Herpes and HPV spread through skin-to-skin contact, while chlamydia, gonorrhea, HIV, Syphilis and Hepatitis B can spread through sexual fluids. If you do choose to be sexually active, consider using condoms 100%, talking to your partner, and getting tested regularly to reduce your risk. Thanks for asking this important question!