So what exactly is the cervix and what does it do?
The cervix is a narrow tube-like structure at the lower end of uterus and it extends into your vagina. Comprising strong muscles and with a length of around 1.2 inches (3 centimeters), the main function of the cervix is to enable the flow of menstrual blood from the uterus to the vagina and also to direct sperm into the uterus during intercourse.1,2 After menstruation and directly under the influence of estrogen, the cervix undergoes a series of changes in position and texture. During most of the menstrual cycle, the cervix remains firm, and is positioned low and closed. However, as ovulation approaches, the cervix becomes softer and rises to open in response to the higher levels of estrogen present. These changes are also accompanied by changes in cervical mucus.3
The cervix during pregnancy
During early pregnancy, your cervix becomes softer and swells a bit – this is due to increased blood flow, which is in turn due to the rising levels of estrogen in your body. In addition your cervix will rise up although it is hard to know exactly when this happens because it is different for every woman. You can actually check the position of the cervix yourself. It is located 3 to 6 inches inside your vagina and feels a bit like a small donut with a tiny hole in the middle. Make sure your hands are clean and your nails are short. Get into a sitting position and move your longest finger into your vagina and you should be able to feel it.
The length of your cervix should remain the same during early pregnancy and it is only in the later stages that it starts to decrease in length and become thinner as your body prepares for labor. The length of your cervix might also change if you have bleeding complications, inflammation, an overstretched uterus, or an infection.1
How is the cervix associated with preterm birth?
If the cervix starts to thin before 37 weeks, you might be at risk of having a preterm birth.
In the event that you experience symptoms and signs of preterm labor, such as frequent or regular contractions, vaginal spotting, pelvic pressure, or a low dull backache, your healthcare provider might perform a pelvic exam to check whether or not your cervix has begun to open.5 They will also probably do an ultrasound to measure your cervical length.
If it turns out that you are in preterm labor, there are treatments you can undergo that can stop or delay labor. If you’re not in active preterm labor but meet certain criteria, such as painless cervical dilation in the second trimester before week 24 of pregnancy, you might be recommended to undergo a cervical cerclage. In this procedure, the cervix is stitched closed with sutures.
In addition, if you have a history of preterm birth, your healthcare provider might recommend progesterone injections to reduce your risk of experiencing another preterm birth.4
The cervix during labor
There are 4 stages in labor: the first stage which comprises early labor and active labor, the second stage which is when you push and your baby moves down the birth canal, the third stage which is when you give birth to the placenta and the fourth stage which is recovery from the birth.6,7
During the first stage of labor, contractions help your cervix to become thinner and to start to open. These processes are called effacement and dilation, respectively, and your healthcare provider will be starting to regularly measure the dilation once you get to hospital. During early labor your cervix will open to around 4 centimeters and during active labor your cervix will open from 4 to 7 centimeters. It is once you reach active labor that you should consider going to the hospital. In addition, if you have contractions every 3 to 4 minutes and each one lasts for around 60 seconds, this usually means that your cervix is now opening quite quickly (around 1 centimeter per hour).5 Another reason to get to the hospital!
During the transition to the second stage of labor, your cervix will open further – from 7 to around 10 centimeters. This is when your cervix opens to its fullest and for the majority of women, this is the most painful stage of labor. The second stage of labor begins once the cervix measures 10 centimeters as the baby can now begin to move down the birth canal.7