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Cervical Length: Why Does It Matter During Pregnancy

4 min read

A healthy baby is the goal of every pregnancy. Certain parts of the body play an important role to ensure an uncomplicated pregnancy and delivery. But in some cases, certain anatomical issues of the mother can make pregnancy and delivery complicated. Cervical length is one such feature.
Cervical length and pregnancy

What Is Cervical Length?

Cervix is the lower part of the uterus that appears like narrow tube which opens to the vagina. Cervical length refers to the length of the tube and the length of the cervical opening. This opening is too small, just enough to allow the menstrual blood and sperm to pass through.
Before pregnancy, the cervix remains rigid. During pregnancy the cervix is closed and sealed with the mucus plug in order to avoid the entry of any infection to the womb and the growing baby.
As pregnancy progresses, the cervix loses its rigidity and gradually starts to open, shorten, get thinner and softer so that the baby can pass easily through the birth canal during labor. This process is called effacing (decreasing the length) and dilating (opening).

What Is The Importance Of Cervical Length During Pregnancy?

Normal cervical length is important for an uncomplicated pregnancy and delivery. This is because, shorter the cervical length, higher the risk of preterm delivery. Also if the cervical length decreases in early pregnancy, the chances of any infection progressing to the womb goes up and this can trigger uterine contractions which can result in preterm delivery.

Is Short Cervix And Cervical Insufficiency Same?

No. Short cervix and cervical insufficiency are both different. Short cervix refers to the decreased cervical length. Whereas, cervical insufficiency is a condition in which the cervix starts to efface and dilate too early in the pregnancy without any signs of contractions or pain. This happens irrespective of the length of the cervix, mainly due to weak cervical tissues.

Factors That Influence The Cervical Length During Pregnancy

The cervical length during the first trimester is entirely based on the maternal anatomical feature or due to a previous cervical surgery. The other factors that influence the cervical length during pregnancy include:

  • Infection in the cervix can result in short cervical length
  • When the uterus is over distended as in case of multiple pregnancies, the cervical length tends to decrease
  • Inflammation of the uterine lining is found to influence the length of the cervix
  • Some complications that appear during pregnancy like bleeding can irritate the cervix. This may influence the cervical length
  • Previous abortion or difficult labor can adversely affect the cervical length in subsequent pregnancy
How Is The Cervical Length Determined During Pregnancy?

Transvaginal cervical scan gives a clear view and correct measurement of the cervical length. As explained earlier, the cervix appears like a tube with one end at the top of the vagina and the other end inside the uterus. The opening into the vagina is called external OS and the opening into the uterus is called internal OS. The length of the cervix is measured from the internal OS to the external OS. The length is generally taken down in centimeters or in millimeters.

  • Normally when the pregnancy gets into the 24th week, the cervix is 35 to 48 mm long
  • If the length is less than 25 millimeters before the gestation reaches 24th week, the cervical length is considered as short
  • If the length of the cervix is less than or equal to 20 millimeters before the gestation reaches 24th week, the cervical length is considered as too short thus increasing the risk of premature delivery

cervix explained

Is The Cervical Length Measured During All Pregnancies?

No. The transvaginal scan for measuring the cervical length is not a part of a routine pregnancy test. This is usually performed on women with high risk of preterm birth, usually before the 16th week of gestation. This is usually recommended for:

  • Multiple pregnancies
  • If the mother has a history of preterm delivery around the 24th week of gestation
  • If the mother has experienced unexplained miscarriage more than once towards the end of the first trimester or during the early weeks of the second trimester
  • If preterm delivery runs in the family
What Can Be Done If The Cervical Length Is Small?

With a short cervix, the expecting mother has a higher risk of preterm delivery. To prevent this, watch out for any of the following signs, especially before the 24th week of gestation.

As we already know, these are the signs of early labor. Seek immediate medical attention. The doctor will closely monitor you and your baby. He will do a pelvic exam to check your cervix. Your doctor may take the following steps:

  • If the symptoms are due to some infection, it is treated
  • If you are not experiencing any contractions, but the cervical length is constantly decreasing or showing signs of dilation before the 24th week of gestation, cervical cerclage is performed. This is a minor surgical process, in which the cervix is sewn closed temporarily and the stitches are removed during labor
  • Tests like fetal fibronectin are conducted to determine the chances of preterm delivery
  • Other precautionary measures like strict bed rest, staying well-hydrated etc. should be taken to bring down the chances of preterm delivery
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