Preterm birth, when babies are born before they’ve had the chance to reach 37 weeks, is one of the more serious health risks a newborn can face, and is a major problem worldwide. The March of Dimes’ “Premature Birth Report Card” shows the rate of preterm birth in the US at 9.6% in 2014, while the World Health Organization estimates that, across 184 countries worldwide, the rate ranges between 5 and 18%. One of the risk factors for preterm birth is a short cervix. Cervical length is not routinely measured during pregnancy, but monitoring is recommended in women at an increased risk for a short cervix, such as those with a prior cervical procedure or a history of a preterm birth. It is also often performed upon request.
How short is too short?
Unless a woman is at an increased risk for a short cervix, the first cervical length measurement often takes place at the time of the anatomy ultrasound sometime between 18 and 20 weeks. On average, a cervix should be somewhere between 3 and 5 cm long during that gestational age window. There is some wiggle-room, but a cervix that’s 2.5 cm long or shorter is considered to be at a higher risk for preterm birth, and will likely be monitored more closely from that point forward.
Cervical length can be estimated by manual exam, but between 16 and 24 weeks it is most often measured by a transvaginal ultrasound. In a transvaginal ultrasound, an ultrasound wand is inserted vaginally, and it emits sound waves that map out a picture of the cervix and uterus.
Why isn’t cervical measurement a standard procedure?
While some healthcare providers perform transvaginal ultrasounds to measure cervical length as a part of their standard procedure, most only measure cervical length in cases where there are other risk factors for preterm birth, like a history of a prior preterm birth, or a cervical procedure. However, many healthcare providers will perform a cervical measurement upon request, so it’s a good idea to have a conversation with your provider about his or her opinion of whether to perform a cervical measurement.
If a provider isn’t affiliated with a hospital or medical center where they perform a transvaginal ultrasound, they can generally provide a referral to a clinic or medical center that does. There are no known risks surrounding transvaginal ultrasounds during pregnancy, and women who are concerned about the possibility of preterm birth may benefit from discussing cervix length with their doctors.
- “Echogenic Fetal Kidneys: Differential Diagnosis and Postnatal Outcome.” IAME. Institute for the Advanced Medical Education, 2014. Web.
- Shannon K Laughlin-Tommaso, MD. “During pregnancy, what’s the significance of cervical length?” MayoClinic. Mayo Foundation for Medical Education and Research, May 2015. Web.
- “Short cervix in pregnancy.” OBFocus. Focus Information Technology, 2014. Web.