Risk Factors for Preterm Labor

Posted On: December 16, 2015 By Andrei Rebarber, MD

Preterm labor is any delivery that occurs between the 20 and 36 6/7 weeks of pregnancy. About 70% of preterm births are spontaneous, while 30% are medically induced due to impending risk for the mother or child. There are many risk factors for preterm labor.

Some epidemiological risk factors include older-aged women; non-white ethnicity, particularly the African American race; medical conditions, like hypertension or diabetes; and lifestyle choices, such as smoking, substance abuse, and poor nutrition. A poor nutritional environment can develop if there is little or no access to prenatal care and limited education on proper food choices.

Women carrying twins have the highest chance of preterm delivery, an almost 50% chance to deliver preterm. Sometimes the mother’s womb, or uterus, has developed abnormally. For example if there’s a septum in the uterus, this is called a uterine congenital malformation. In these cases, women usually don’t find out until they are actually pregnant, after delivering a premature baby, or during an infertility work up. A prior history of preterm labor is the single biggest risk factor for premature delivery after twin gestation.

Symptoms of preterm birth are nonspecific and are often similar to symptoms of a normal pregnancy. They can include pelvic pressure, back pain, and an increase in vaginal discharge. There are four main biologic pathways leading to preterm labor risk factors:

  1. Infection.
  2. Decidual hemorrhage, or bleeding during the pregnancy, particularly more than once in several trimesters.
  3. Abnormal stretch of the uterus, whether it be an excess of amniotic fluid or twin pregnancy.
  4. The activation of the maternal or fetal hypothalamic-pituitary-adrenal axis that causes fetal or maternal stress, leading to a hormonally activated labor.

Our single best preventative strategy available for women at risks for preterm labor (i.e. those with a prior history of a singleton preterm birth) is to administer an injection of progesterone or Makena. This treatment has been associated with a significant reduction in the recurrence of preterm birth by about 30%.

Biomarker screenings can also help detect patients at high risk of preterm labor, whether patients are symptomatic (i.e. contractions) or not.  Biomarker screening with either a transvaginal ultrasound measuring the cervical length, or utilization of a test called fetal Fibronectin (fFN) can indicate the physiological state of the mother and baby and may adjust her risk of imminent preterm birth.

The most effective way to decrease the chance of preterm birth is to consult with your medical provider and obtain a preconception consultation. Review your prior medical history and previous pregnancy outcomes, modify risk factors related to lifestyle if possible, and get regular prenatal care throughout your pregnancy.

Carnegie Imaging for Women blogs are intended for educational purposes only and do not replace certified professional care. Medical conditions vary and change frequently. Please ask your doctor any questions you may have regarding your condition to receive a proper diagnosis or risk analysis. Thank you!

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