As estrogen levels rise during pregnancy, yellow vaginal discharge often occurs. Yellow discharge can also be caused by bacterial infections, which, if left untreated, may harm your pregnancy. Conditions such aschlamydia, gonorrhea, and trichomoniasis can result in yellow discharge. In addition, uncomfortable underwear or unhygienic products may also cause discharge. If you are experiencing discharge and itchiness, foul odor, or vaginal pain, call your doctor