Why the cervix is so important during pregnancy
“This might be a stupid question, but what’s a cervix?” asks a dad-to-be at a prenatal class.
If you’re learning about the mechanics of childbirth in detail for the first time, this part of a woman’s anatomy is going to come up a lot. The cervix is the narrow neck of the uterus—picture the opening at the bottom of a balloon—which keeps the uterus closed until it’s go time.
“During early pregnancy, the cervix is really firm and closed, pointing to the back of the vagina,” explains Nicola Strydom, a registered midwife in Calgary. “A mucus plug forms inside the cervix to protect the baby from bacteria.” It’s not abnormal for the cervix to bleed a little during pregnancy, especially after sex, due to all the tiny blood vessels.
Between 37 and 42 weeks of pregnancy, the cervix tends to shift forward, pointing toward the front of the vagina. It gets softer and starts to widen and open (also known as dilating), and thin (or efface). If this isn’t your first baby, the cervix is already softer and a little more open than a first-time mom’s.
About one percent of pregnant women have a cervical problem, known as an incompetent cervix or cervical insufficiency. (Yep—those are the technical medical terms.) This means the cervix is weak and starts to open, shorten or form a funnel shape partway through pregnancy, which may contribute to an increased risk of preterm birth. The problem could just be how your body is made, but according to the Society of Obstetricians and Gynaecologists of Canada (SOGC), you’re at higher risk if you’ve had a prior pregnancy in which your water broke earlier than 32 weeks, or if you have had some kind of cervical trauma, such as a cervical tear, cervical cancer or repeated D&Cs.
Between 14 and 20 weeks, a woman with cervical insufficiency may have vague symptoms like backaches, pelvic pressure, mild abdominal cramps, light vaginal bleeding or a change in vaginal discharge, but some women have no signs at all.
“It’s a problem that is quite silent,” says Marie-France Delisle, a maternal-fetal medicine specialist in Vancouver and co-author of the SOGC clinical guidelines on cervical insufficiency. During an internal exam, your doctor may find that the cervix is slightly open and the amniotic membranes are bulging. A short cervix may be detected during the regular abdominal ultrasound at 18 to 20 weeks, requiring a follow-up with a transvaginal ultrasound. Treatment varies, says Delisle, from going on modified bed rest (you can only get up for meals or bathroom breaks) to a daily vaginal suppository of progesterone to keep the cervix from shortening further. Some doctors may prescribe a device placed in the vagina, called a pessary, to help support the cervix.
Another option is cerclage, a day surgery in which one continuous suture is used to close the cervix. A preventive cerclage could be done at 12 to 14 weeks (if you have a history of cervical insufficiency) or up to 24 weeks (if it’s found later). The suture is removed around week 37.
Jennifer Gray, of Grande Prairie, Alta., and mom of Parker, 3, and one-year-old twins Nathan and Garrett, dealt with cervical complications during both pregnancies. She wasn’t able to have a cerclage in either case. Her doctors prescribed bed rest and, in the case of the twins, a pessary. While these measures work for many women, they didn’t work for Gray—Parker was born at 29 weeks and the twins at 25 weeks. Parker is doing fine but the twins face prematurity-related health issues. “My body was failing me and there wasn’t anything I could do to stop it,” Gray says. “It was terrifying.”
For most women, though, the cervix works just fine. During labour—or even in the weeks leading up to your due date—your cervix slowly begins to dilate. When the opening gets to 10 centimetres, it’s time to push, and you finally get to meet your little one.
What is a cervical sweep?
Between 39 and 41 weeks of pregnancy, your doctor or midwife may offer to do a membrane sweep—putting a gloved finger into the cervical opening to separate the amniotic membrane from the cervical tissue. (Not gonna lie: It will likely hurt, though how much varies woman to woman.) A sweep is considered a low-risk, drug-free way to help encourage labour because it stimulates the uterus to start producing prostaglandins, which can soften the cervix.
A version of this article appeared in our January 2017 issue, titled "At your cervix," pg. 51.