In the United States, premature birth is the leading cause of permanent disabilities, and sometimes death in babies. In many cases, it is unclear why a woman experiences preterm (premature) birth. A baby that is born before the 37th week of pregnancy is considered preterm.
Physicians and scientists continue to study the various causes of preterm labor, which may allow them to identify risk factors that would cause a woman to be at an increased risk of delivering her baby prematurely. This area of research is very important, because once preterm labor starts, it may be very difficult, and sometimes impossible, to stop it.
One method that is used to help predict which women will experience premature labor is by measuring the length of her cervix (the opening to the uterus). One of the first changes that occur in a woman’s body before she goes into labor is shortening (effacement) of her cervix. The cervix may begin to shorten weeks before labor starts. If the cervix is shorter than normal early in her pregnancy, she has a higher risk of premature labor. Based on this risk, her physician can offer treatments to reduce her risk of, or prevent, premature labor.
The most accurate method to check the length of the cervix is by transvaginal ultrasound. Because the cervix begins to thin, or shorten, from the inside, the ultrasound can detect this before a woman’s physician or midwife could when performing a vaginal exam.
If you have already delivered a baby that was not born prematurely, or if you are expecting your first baby, it is recommended that measuring the length of your cervix is done as a part of a routine ultrasound between the 18th and 24th week of pregnancy. If the length of the cervix is within the normal range, there is no need to repeat an ultrasound for the purpose of measuring the cervix.
Women who have a history of delivering a baby before the 37th week of pregnancy due to premature labor have an increased risk of premature labor in future pregnancies. Due to this increased risk, if you experienced preterm labor and delivered a baby before your 37th week of pregnancy, The Society for Maternal-Fetal Medicine recommends that you have the first transvaginal ultrasound to measure cervical length between the 14th and 16th week of your pregnancy, followed by additional ultrasounds.
One drug that has proven to reduce the risk of preterm birth is called 17-alpha-hydroxyprogesterone caproate, which is a form of progesterone. It’s also known as “17P.” In 2011, the Food and Drug Administration (FDA) approved this drug for the prevention of preterm delivery. It is available in three forms, a pill, injection (shot), or vaginal suppository. Women who take progesterone usually begin in the 16th week and stop when they reach the 36th week of pregnancy. How often it is given depends on what form of the medication is prescribed.
If you have a history of a preterm delivery, talk to your physician or midwife. He, or she, will be able to answer questions based on your personal history.
Berghella, V. (2017). Second-trimester evaluation of cervical length for prediction of spontaneous preterm birth in singleton gestations. UpToDate. Retrieved from https://www.uptodate.com