Cervical OS in Pregnancy, Childbirth and postpartum

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By John Wick

Internally, the female reproductive system consists of the vagina, uterus, ovaries and fallopian tube. The lower part of the uterus is connected to the uppermost part of the vagina via a ring or elongated doughnut-shaped muscular structure called the cervix. Cervix bridges the gap between the vagina and uterus.

Structure of cervix

It has a narrow tube-like opening which runs throughout the structure. It is approximately 1 -2 inches in length. Both openings of this cervix are called os. The end towards the uterus is known as an internal os and the end towards the vagina is known as an external os.

The function of the cervical os

Like all the other organs of the female reproductive system, the role of the cervix also changes throughout women’s menstrual cycle. Both opening of the cervix i.e. internal os and external os will open and close also the position will be higher or lower in different phases of the menstrual cycle. 

However, sometimes some women are born with a cervix that seems to be closed at all times or it’s narrow or completely blocked. This is known as cervical stenosis. This can be present since birth or developed later on in life. There are several factors like age, uterine surgeries, cancers, scarring or internal growths responsible for developing this stenosis.

If you are trying to conceive or having painful symptoms, always consult your doctor who can guide you to the proper line of treatment and care. 

  • Ovulation

During ovulation, the position of the cervix is highest and the opening becomes wider to allow the passage of sperms for conception. In this phase, the secretion of the cervix also becomes thinner and more alkaline to favour the movement of sperm and helps in sperm survival. 

  • Other days of the cycle

During other days of the cycle, the cervix is closed tighter and secretions are thicker and acidic. This provides protection against bacteria and other infective agents.

  • Pregnancy

In pregnancy, the main role of the cervix is to maintain the foetus inside the uterus and allow passage when term is complete.

OS in pregnancy

By now you must have realised how dynamic this part of your body is and its importance throughout your pregnancy and even afterwards. Let’s look at how and what is the role of cervical os in your pregnancy.

  • During entire term of pregnancy

The sole job of cervical os in pregnancy is to keep the baby inside the uterus even when the baby moves downwards closer to the opening in the last phases of pregnancy. This is done with the help of mucus plug. This also prevents entry of any microorganism in the uterus and provides a safe and sterile environment for the growing baby.

  • Dilation and labour

As you move towards the end of term anywhere between 37 and 42 weeks, the cervix undergoes rapid changes to enable passage of the foetus from the uterus down through the vaginal canal. Cervix becomes shorter, softer and wider. This process is called effacement.

  • Early labour

This is the first stage of childbirth where you will experience regular contractions which progressively increase in intensity and occur at shorter intervals. This phase is the longest phase.  It differs in length of time from person to person – It can last for a few hours or even days. However, with subsequent deliveries it becomes shorter.

These contractions cause the cervix to open (dilate) and soften as well as shorten and thin (efface) to allow your baby to move into the birth canal. Cervix is dilated about 2 inches.  Mucus plug will come off in this phase.

  • Active labour

In this phase, contractions are stronger than the early stage and occur more frequently. The cervix is dilated upto 6-10 cm. you may experience water break in this phase. This generally lasts 4-8 hours.

Your doctor or nurse will examine your cervix dilation in order to predict progress of your labour and if any emergency is likely to arise. When your cervix is dilated sufficiently, Your doctor will ask you to push with each contraction but only after the cervix has sufficiently dilated. Pushing too soon may cause the cervix to swell and might delay the delivery process.

Knowing the cervical dilation is necessary for vaginal delivery, doctors can facilitate cervical dilation during the induction of labour. This can be done with the help of certain medicines or mechanical methods. 

Cervical os postpartum

While internal os closes immediately after childbirth, external os may take several weeks to return to its original size and shape. 

To summarise, the cervix is critical to conception and the maintenance of pregnancy.  Internal os is important for preserving effective barriers for microorganism entry into the uterus. Structural abnormalities can pose the risk of preterm birth or complications in labour. And because of its elastic nature which allows it to thin and dilate during labour and retract to its original shape and place after labour- a miracle of birth is possible.