Hello, Yellow discharge while in labor can mean either an infection, meconium staining if the membranes are ruptured, or blood mixed white discharge as the mucus plug has been lost. Please maintain good genital hygiene and watch for fetal movements. Also, since you have a threatened preterm labor, it is advisable to elevate the foot end of the bed and try to lie on the left lateral side to allow better fetal blood supply from the placenta. Urinary infection, vaginitis and cervicitis should also be excluded and treated if needed. Wish you safe motherhood.