Preterm labor is characterized by contractions or irritability of the uterus between weeks 20-36 of gestation that cause effacement and/or dilatation of the cervix.
The usual length of a human pregnancy is from 37 to 42 weeks after the first day of the last menstrual period. The baby is more likely to survive and be healthy if it remains in the uterus for the full term of the pregnancy. Between eight to ten percent of births in the United States are preterm births. Preterm labor is the greatest cause of newborn illness and death in the United States.
Causes and symptoms
The causes of preterm labor are often not identifiable. Women with a previous history of preterm labor have the highest risk of developing it again, between 17 and 37%. Other risk factors are: low socioeconomic status, minority race, maternal age less than 18 or greater than 40, premature rupture of membranes (bag of waters), multiple gestation (twins, triplets, etc.), harmful maternal behaviors (smoking, drug use, alcohol use, no prenatal care), uterine abnormalities (fibroidtumor, abnormally shaped uterus, incompetent cervix, exposure to diethylstilbestrol—their mothers took DES when they carried them), infectious causes (infection of the uterus, kidney infection), fetal causes (intrauterine fetal death, intrauterine growth retardation, birth defects), and abnormal implantation of the placenta.
The symptoms of preterm labor can include contractions of the uterus or tightening of the abdomen occurring every 10 minutes or more often. The uterine contractions of preterm labor, sometimes painful, will usually increase in frequency, duration, and intensity. Other symptoms associated with preterm labor can include menstrual-like cramps; abdominal cramping with or without diarrhea; pressure or pain in the pelvic region; low backache; or a change in the color or amount of vaginal discharge. As labor progresses the cervix, the opening of the uterus, will open (dilate) and the tissue around it will become thinner (efface). Premature rupture of membranes (when the water breaks) may also occur.
An occasional contraction can occur anytime during pregnancy and does not necessarily indicate that labor is starting. Premature contractions are sometimes confused with Braxton-Hicks contractions, which can occur throughout the pregnancy. Braxton-Hicks contractions do not cause the cervix to open or efface and are considered "false labor."
Nadine M. Jacobson R.N., The Gale Group Inc., Gale, Detroit,