The following obstetric independent variables were also included: parity (nulliparous, parous), pre-pregnancy diabetes (no, yes), gestational diabetes (no, yes), pre-pregnancy hypertension (no, yes), gestational hypertension (no, yes), hypertension eclampsia (no, yes), previous preterm birth (no, yes), infertility treatment (no, yes), infertility medication (no, yes), Assisted Reproductive Technology, previous cesarean section (no, yes), gonorrhea (no, yes), syphilis (no, yes), chlamydia (no, yes), hepatitis B (no, yes), and hepatitis C (no, yes). Here, PPIB is linked to syphilis.