Causes
STIs are usually caused by bacteria or viruses. Your chances of getting them are highest if:
- you have unprotected sex
- a condom tears during intercourse
- your sexual partner has an STI
- your partner is engaging in sex with other people
In some cases, such as with HIV or hepatitis B, viruses can also be spread through infected blood or shared needles and syringes, including those used for drugs, body piercing, or tattoos. Pregnant women can pass certain infections (e.g., HIV) on to their babies prior to or during birth, or while breast-feeding.
Growth of genital warts caused by HPV may appear during pregnancy because of
changes in hormone levels.