I wasn't sure what this was, never heard of it so googled it, here goes:
If you have had late miscarriages (in the second trimester) or premature births, you may be advised to have scans to measure the length of your cervix (neck of the womb), in future pregnancies. This is to look for early signs of the cervix opening before the baby is due. Cervical length scans may also be recommended if you are expecting twins or have had surgery to your cervix.
Your cervix should stay closed throughout pregnancy until just before the birth. If the cervix starts to open prematurely, the pregnancy may be lost. The cervix has a plug of mucus in it known as 'the show' and if this comes away early, infection may get into the womb. It is not known whether infection gets in because the cervix is not tightly closed or whether the infection causes the cervix to open, but it is vital to treat any infection promptly.
Until about 10 years ago, women at high risk of premature opening of the cervix were advised to have a stitch put in to keep the cervix closed but no one knew for sure whether or not it was really necessary. The procedure itself can introduce infection or break the bag of waters (rupture the membranes), so should only be done if absolutely necessary. Nowadays, the length of the cervix can be measured and a stitch put in only if the cervix is shortening or beginning to open. (Read more about having a cervical stitch.)
A vaginal scan is the best way to measure your cervix because it can be seen much more clearly this way. The cervix looks like a tube on the scan, between 3 and 5 cms in length, with one end at the top of the vagina (the external os) and the other end inside the womb (the internal os). It is the internal os that can begin to open first and this will look like a V shape on your scan. As the os opens further it becomes U shaped. This is called funnelling. If the closed part of the cervix measures less than 2.5 cms, a stitch will be put in to stop the cervix opening further. This will be done in hospital under a general anaesthetic.
When the scans are performed depends on your obstetric history. It may only be necessary to look at 16, 20 and 24 weeks; if your cervix is long and closed each time, no more will be necessary. Sometimes fortnightly scans are performed throughout the second trimester and vaginal swabs taken, to look for infection.
Normal labour is usually accompanied by painful contractions as the cervix opens but a weak, ('incompetent') cervix opens 'silently' with no pain or bleeding. That is why it is important to have regular scans to look for early signs.
There are no risks to you or your baby in having vaginal scans. By having these scans, you will only have a stitch put in if it is truly necessary. If you do have a stich put in, it will be removed a few weeks before your due date.
try to stay positive, the drs have you and your baby's best interests at heart!
