Is cervical length ultrasound needed to prevent preterm birth?

I am 13 weeks pregnant and previously had a preterm birth at week 33. Do I need an ultrasound to measure cervical length, and when should it be done? (Phuong, Quang Nam)

Answer:

Given your history of a preterm birth at week 33, your uterus may be more sensitive, or the pressure from the fetus from the second trimester onwards could cause your cervix to shorten earlier than usual. Therefore, it is advisable for you to undergo a transvaginal ultrasound to measure cervical length.

Measuring cervical length via transvaginal ultrasound is a method to assess the risk of preterm birth. This allows doctors to intervene promptly to keep the fetus in the womb for as long as possible. The procedure is considered safe and offers higher accuracy compared to abdominal ultrasounds for cervical length assessment, addressing common concerns about its impact on the fetus.

For individuals with a high risk of preterm birth, such as those with a history of preterm birth, miscarriage in the second trimester, previous cervical surgery, or uterine abnormalities, cervical length measurement should be performed earlier, starting from week 16. For most pregnant individuals, this measurement is typically done between week 18 and week 24.

The cervix is a funnel-shaped structure connecting the vagina and the uterus. Its normal length ranges from 30-50 mm, featuring a central canal with internal and external openings. During pregnancy, the cervix remains closed, sealing the uterine cavity from the vagina. As labor progresses, the cervix gradually dilates and opens for the baby to be delivered vaginally.

A cervical length of less than 25 mm before week 24 signals a potential risk of preterm birth. Depending on the findings, you may require regular ultrasounds every one to three weeks to closely monitor any changes in your cervix. If you are at high risk of preterm birth, your doctor might recommend progesterone suppositories or a cervical cerclage as preventive measures.