When you meet with your OB for your 20-week appointment, they’ll likely perform a transabdominal ultrasound. That’s the one where they squeeze the gel onto your abdomen and move a probe over the surface of your skin to look inside your uterus. It’s an exciting milestone to capture images of baby and examine every last inch of them from head to toe. While that 30-60 minute ultrasound can be helpful in seeing so much of what’s going on with your placenta and baby, it’s not the ideal way to measure the size or length of your cervix, the small opening at the bottom of your uterus.
What is a cervix, and what should I know about cervical length?
The cervix is an important part of pregnancy, labor and birth. In most cases, it stays long and almost totally closed until the end of pregnancy. Unless you’ve had cervical surgery or a previous preterm birth, your OB might not specifically look at your cervix or check to see if you have a short cervix. A short cervix is usually defined as a cervix that is less than 2.5 cm long. The average range of a cervical length during pregnancy is 3 to 5 cm, and that length will shorten as your pregnancy progresses. A short cervix before your 24th week of pregnancy is one of several risk factors for preterm birth, which comes with serious risks for the baby. If you want to know whether you have a short cervix but don’t have a worrisome medical history, you may need to request a transvaginal ultrasound at the time of your 20-week scan.
How is a cervix measured?
Unlike the abdominal ultrasound, which runs a probe on the surface of your skin to pick up images of your baby, a transvaginal ultrasound requires a probe to be inserted two to three inches into the vagina to get a picture of your cervix. This is commonly the type of ultrasound you have in early pregnancy as well! It can create images of your reproductive organs and give your provider a clear picture of your cervical length. It takes 1-2 minutes, and it gives your healthcare provider the most accurate picture of your cervix and whether you are at increased risk of preterm birth. Having this information means that steps can be taken to reduce your risk and protect your pregnancy for as long as possible.
Talking to your provider
Cervical length can play a large part in determining the risk for preterm birth. If a short cervix is caught early in a pregnancy, there are some things your provider can do to reduce your risk of giving birth early. Because of this, it’s worth asking to look at your cervical length between your 16th and 24th week of pregnancy. While some providers already make this their routine for all parents to be, it’s an easy conversation to have ahead of your 20-week appointment.
Sources
- “Cervical insufficiency and short cervix.” March of Dimes. March of Dimes Foundation. August 2015. Web.
- “Preterm (Premature) Labor and Birth.” ACOG. American College of Obstetricians and Gynecologists. November 2016. Web.
- “Management of Pregnancies With Cervical Shortening: A Very Short Cervix Is a Very Big Problem.” Obstetrics & Gynecology. U.S. National Library of Medicine. National Institutes of Health. 2009. Web.
- “Transvaginal ultrasound.” MedlinePlus. U.S. National Library of Medicine. May 16, 2016. Web.
