Does this Cervical Length Indicate Incompetent Cervix?

QUESTION

Dear Ms Ultrasound,
At my ultrasound (19 weeks, 2 days) the technician measured my cervical length at 3.4 cm. She said it was good, but I'm worried because I thought it should be closer to 4 cm. Plus for some reason I'm thinking that at my 12-week u/s the length was closer to 4. But I could be remembering wrong. In fact, I'm not even sure the technician at 12 weeks had told me my cervical length! (Pregnancy brain!)

I'll hopefully talk to my doctor next week when he gets the report, but I was just wondering.

ANSWER

Hi, My first question to you is why are they worried about your cervical length? If you have had an incompetent cervix in previous pregnancies, that would explain the interest. I will assume this is the case.

An Incompetent Cervix is the shortening of the cervix during pregnancy. This results in a weakened cervix and the amniotic membranes bulging into the internal cervical os, eventually causing the amniotic membranes to rupture and an early delivery. If an incompetent cervix is caught early enough, a special suture called a Cerclage is sewn in which holds the cervix closed until delivery.

The normal length of a cervix during pregnancy is 3 centimeters or greater, so your 3.4cm cervical length is within normal limits. The length may vary depending on how full your bladder is during the ultrasound and whether or not the ultrasound was done vaginally or not. A vaginal ultrasound is the most accurate way to measure a cervix. From 32-34 weeks gradual cervical shortening begins, so a measurement of less than 3 cm can be normal in the last trimester.

When an incompetent cervix is being followed, the best bet is to have an ultrasound in the 12-14 week time frame to get a baseline measurement. Sounds like this is what your doctor has already done. In subsequent ultrasounds, if the cervix measures short, a follow-up ultrasound should be done within 24-48 hours.

From the results you have been given from your last ultrasound, you are in the normal range and 'in the normal range' are always very comforting words to a Mother-to-be's ears.

-- Jane, RDMS

Jane Foley

Jane Foley has worked as a Sonographer (Ultrasound Technologist) since 1979. Jane has lived and worked in many parts of the world including Saudi Arabia. She is a Registered Diagnostic Medical Sonographer or RDMS. She pulls a wealth of information from her experience in the field of Radiology and her interactions with such a broad cross-section of cultures she has visited. She now makes her home on the island of Maui with her English husband, Michael.