Doctor's Notes on Signs of Labor
Labor, used as a medical term, means the process of childbirth, from the start of regular uterine contractions to delivery. Labor is a sign and symptom of delivery. Some physicians include lightening, which involves the baby dropping down into the pelvis (short of breath, feel heavy or pressure, increased urination) that occur before normal uterine contractions begin. Bloody show, a brownish vaginal discharge and/or blood tinged mucus plug, may be discharged along with irregular false labor pains can occur before labor and “water breaks” refers to the leaking or disruption of amniotic membranes causing fluid to leak from the vagina, usually a sign that labor time is near. Some consider these as pre-labor signs. Signs and symptoms of labor are dilation of the cervix opening and increasing shortening of times between painful uterine contractions that continue until the baby is expelled from the vagina (delivery).
The exact cause or trigger of labor is not exactly known; however, researchers consider that hormone changes in the baby and the mother likely interact to trigger labor. For example, oxytocin from the fetus and mother may stimulate the uterus to contract and trigger prostaglandins which, in turn, open the cervix and also facilitate uterine contractions.
Kasper, D.L., et al., eds. Harrison's Principles of Internal Medicine, 19th Ed. United States: McGraw-Hill Education, 2015.