Preterm birth, a serious complication in pregnancy occurs in 6-8% of women. The risk of spontaneous preterm birth increases as the length of the cervix (neck of the womb) decreases. Ultrasound scanning may be used to assess the length of the cervix in women at high risk of preterm birth. We will recommend an assessment after 16 weeks in high risk pregnancies. There is no proven benefit in assessing the cervix by ultrasound in women with no risk factors for preterm birth.
Who is at risk:
• Prior very preterm birth (<32 weeks gestation)
• Previous cervical surgery (eg. cervical cone biopsy)
• Women with a cervical suture
• Women with suspected cervical incompetence
• Multiple pregnancies
Cervical Length Scan
What is a normal cervical length in pregnancy?
• At 20 weeks gestation the average cervical length is 40mm
• At 34 weeks gestation the average cervical length is 34 mm
How do we assess the cervical length?
A transvaginal ultrasound examination is required to accurately measure the length of the cervix. We check for the following:
• Length of the cervix (normally >25mm)
• Funneling of the membranes at the internal os.
• Dilatation of the cervix
• Location of a cervical suture (if present)
What may happen if it is found that the cervix is shortened or dilated?
If your cervix is shown to be shortened we will liaise with your healthcare team and hospital, letting them know our findings and provide them with a report, we will also organise any follow-up appointments you may need.
