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Premature Labor

What Causes Premature Labor?

Last modified: 
23/04/2012 - 15:45

Contributing Author: Guy Slowik FRCS

The mechanism that causes normal term labor to begin is not completely understood, so the actual cause of premature labor is also unknown. However, there are some factors that may increase a woman's risk for premature labor.

Risk factors in a woman's medical history that can lead to premature labor include:

  • Infection in the cervix or uterus
  • A previous premature delivery
  • Multiple pregnancy - twins, triplets, etc.
  • Poor socio-economic status
  • Previous miscarriages or terminations of pregnancies (especially if these were repeated and late)
  • Premature rupture of membranes
  • Previous surgery on the cervix (line conization)
  • Exposure to diethylstilbestrol (DES), a synthetic estrogen commonly given to pregnant women between 1938 and 1971. DES is no longer used because of a link to birth defects.

Nice To Know:

While twins account for 1 in 80 of all pregnancies, they account for 1 in 10 preterm births. 50 percent of twin pregnancies deliver prematurely.

Induction Of Premature Labor

While it is normally desirable for a pregnancy to reach its full term, there are circumstances in which obstetricians must induce preterm delivery for the safety of the mother, the child, or both. One of the following may necessitate the induction of preterm labor:

  • Severe hypertension or eclampsia, or a seizure or coma in a woman with pre-eclampsia; a condition occurring during the second half of pregnancy characterized by high blood pressure, swelling, and large amounts of protein in the urine.
  • If the amniotic sac ruptures prior to the 37th week of pregnancy, this is a condition known as preterm premature rupture of the membranes (PPROM). The decision to induce preterm labor will depend on the gestational age of the fetus and the presence of an infection.
  • Fetal stress, where evidence of poor growth and lack of oxygen is discovered.

Normally, every effort is made to assure that a baby is as mature as possible prior to delivery. In some cases, however, even a very premature baby is better served by Neonatal Intensive Care Unit (NICU) facilities than by continued dependency on a less-than-healthy uterine environment.

Can My Doctor Predict Whether I Am At Risk?

In many cases, premature labor occurs without any known risk factors, making it very difficult to predict which women will deliver preterm.

Because of the difficulty in predicting premature labor risk, all pregnant women should be familiar with the signs and symptoms of preterm labor.

Can Premature Labor Be Prevented?

  • Many measures designed to prevent premature labor have not been proven to work in well-designed scientific studies. These include complete bed rest, oral medications to stop contractions, machine monitoring of contractions at home and pump subcutaneous injections of tocolytic medications to stop contractions.
  • In women with an abnormal or deformed cervix that opens prematurely (incompetent cervix), putting a stitch (cerclage) around the cervix to prevent it from opening is often done to prevent premature labor.
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From Andrew Maynard - Chair of the University of Michigan Department of Environmental Health Sciences, with help from David Faulkner - 2013 Master of Public Health graduate.