The fact is that most women know when the onset of labor begins by instinct, luck, and, very often, by killer contractions. No one really knows what actually triggers labor, but a group of natural substances produced by the body stimulate uterine muscle to contract. Probably a combination of fetal, placental, and maternal factors work together to set labor into motion. This is rarely true of later births, as the fetus descends when labor begins. Usually, weight gain slows during the ninth month, and, as labor approaches, some women actually lose 2 or 3 pounds.
Some mothers have increasing fatigue.
Others have energy spurts. Vaginal discharge may thicken or increase. This piece of mucus can be passed through the vagina a week or two before real contractions or just as labor begins. Capillaries frequently rupture as the cervix effaces and dilates, tinting the mucus pink or streaking it with blood. The Braxton Hicks contractions, which have been practicing for several weeks, may become more frequent and stronger.