The cervix is the cylindrical mouth of the uterus, separating it from the vagina. Normally, the cervix is at least 3-4 cm long (about 1 1/2 inches), and its length in pregnancy strengthens the protection of the fetus. Toward the due date, the cervix normally shortens significantly (effacement) as the body prepares for labor and delivery.

Taking care of yourself throughout your pregnancy is the best possible prevention for preterm birth. This means avoiding habits like overeating and smoking are recommended. Sometimes, women who remain healthy still deliver preterm without reasonable explanation. However, there are studies suggesting a very obvious and physical predictor as to whether or not you will deliver your baby preterm.

Upon delivery, your cervix will slowly open up and dilate so that your baby can be pushed out. Some women have a shorter cervix than others, and this physical characteristic might change the course of natural labor. Women with a shorter cervix are more likely to give birth preterm. Preterm labor, defined as birth before 37-weeks of pregnancy, is more common in these women because it is easier for the baby to fit through the birth canal even before it is fully dilated. The amniotic sac will begin bearing down on the opening as the baby grows heavier, and labor contractions could begin.

When you become pregnant, you should consider getting an ultrasound to determine your cervical length. If you know your cervix is shorter than normal, you can prepare yourself for preterm labor. Even if you don’t take the measures to prevent it, preterm labor will be safer if you and your physician are prepared to take on the challenge. If your physician determines that there is a good chance you might deliver preterm, he or she might suggest you get a cervical cerclage, or a stitching of the cervix to prevent labor before the 37th week. You may also be advised to take bed rest in your last trimester to prevent any unnecessary pressure on the birth canal.

A short cervix is probably not a feature you’ve ever included in a physical description of yourself, but when you become pregnant, it could become the difference between a preterm infant and a baby that has grown to term. Talk with your physician about the length of your cervix to find out whether or not it could pose a problem someday.

Studies have shown that cervical measurements done by transvaginal ultrasound between 18 and 28 weeks can predict the risk of premature delivery. The shorter the cervix, the more likely it is that there is a risk for premature labor and delivery. As pregnancy progresses closer to the due date, the cervix normally becomes shorter.

In one study, published in JAMA, Dr. Owen and researchers found that women whose cervixes had shortened to less than 25 mm in length by the time of the first ultrasound evaluation at or after 16 weeks of pregnancy were 3.3 times more likely to give birth prematurely than were the other women in the study. Women whose cervixes had not shortened until later ultrasound evaluations were also more likely to give birth prematurely.

Does bed rest help with a short cervix in pregnancy?

According to a new study published in the journal Obstetrics and Gynecology, bed rest for women with a short cervix does not help deter early birth. More than 600 women were interviewed for the study. The majority of women placed on rest of any kind were covered by private insurance and tended to be older than women who were not placed on activity restriction. Based on information collected by researchers, women placed on rest (with a short cervix) were more likely to give birth early- the opposite effect doctors were hoping for. 

What Does This Study Mean to Women Looking at Bed Rest?
Though the study suggests no benefit from bed rest for women with a short cervix, obstetricians are not likely to change their treatment methods just yet. The study was relatively small with less than 700 participants. Information was revealed using questionnaires – there was no mention of medical record review to reinforce information provided by study participants. If future studies with medical record review and more participants are completed, treatment protocols may be changed to reflect the ineffective nature of bed rest for certain pregnancy complications. 

There are several approaches to a short cervix in the first and second trimester: