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Internal OS Closed: What Does It Mean in Pregnancy Scan Report


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A woman’s body undergoes a lot of changes during the pregnancy period. Not just externally but internally as well. If you are a first-time mother who is entirely clueless about medical terminologies, coming across the term “Internal OS Closed” can sound daunting. However, be assured that there’s nothing wrong with you or the baby.

The Internal OS is part of the cervix and should remain closed during the pregnancy. This prevents premature delivery and supports a healthy full-term pregnancy ride for the mother and the child.

However, if you aren’t sure what an Internal OS closed means in your pregnancy scan report, let us clarify them for you in detail. Before that we shall answer you right away what does Internal OS Closed mean in pregnancy scan report.

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What Exactly Does Internal OS Closed Mean in Pregnancy Scan Report

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The internal cervical os plays a very crucial role during pregnancy and childbirth. If your pregnancy scan reports say, “Internal OS closed”, it is normal during pregnancy. Remember that the internal os should remain closed until your baby is ready to be delivered. If the os isn’t closed, it can lead to many pregnancy complications that need immediate medical interventions. 

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Understanding the Anatomy of the Cervix

The cervix is a crucial and definitive part of a woman’s reproductive anatomy. It is present in the pelvic region and joins the vagina and the uterus, forming a canal. The cervix typically measures 1.5 inches in length and is composed of collagen-cell tissues that contribute to its flexibility and adaptability throughout the pregnancy.

Despite being just 1.5 inches long, the cervix has four distinctive parts.

Ectocervix – comprises the lower third of the canal.

Endocervix – comprises two-thirds of the canal.

External OS – opening on the vaginal side of the canal.

Internal OS – opening on the inner side, towards the uterus side of the canal.

The Internal OS remains closed throughout the pregnancy term and gradually opens during labor and childbirth for a successful and healthy delivery of the newborn.

What is the Role of Internal OS during Pregnancy and Childbirth?

The internal OS is subjected to many changes during the pregnancy and eventual childbirth. Keep in mind that the role of the cervical os isn’t just during pregnancy. It has equally important functions before a woman gets pregnant.

Once the egg and sperm are fertilized and the embryo implants into the uterus, the internal cervical os undergoes subjective changes depending on the stage of the pregnancy.

The primary role of the internal os stands out during the second and third trimester of the pregnancy. Since the fetus is gradually descending towards the birth canal, preparing for its delivery, the cervix prepares itself to provide stability to the developing fetus.

Before labor

During the earlier pregnancy stages, especially the first to second trimester, the internal os must remain closed. This prevents the risks of premature delivery of the baby.

If the internal os loosens and opens up, it can trigger early labor, leading to the baby’s premature birth, with complications.

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During labor and childbirth

As the pregnancy hits close to the delivery date, the cervix changes its texture and appearance. The cervix becomes a lot softer and more flexible to promote the safe delivery of the baby.

Once labor hits, that’s when the internal os starts to dilate. Since the woman needs to be dilated 10 centimeters (4 inches) for a successful delivery, the cervix begins opening up to accommodate the baby’s head for a safer delivery.

As the cervical canal becomes wider, the structure of the cervix becomes shorter and thinner. During this phase, the distance between external and internal OS becomes shorter.

How to Self-Examine the Cervical os?

Not just during pregnancy, one can feel their cervical os during regular days, too, with a simple self-examination. You can sanitize and clean your hands and fingers and then insert two fingers into your vagina to feel the back of the cervix.

Doing a self-examination is ideal for women who are trying to conceive. Feeling the cervical OS can tell you if you are in your fertile stages. When a woman is ovulating, the cervical os is quite relaxed to promote successful fertilization and implantation of the embryo.


Somapika Dutta (B.Sc Physiology, Honours)
Somapikar holds Bachelors Degree in Physiology from University of Culcutta. She has 6+ years of experience writing in different niches, including health, tech and lifestyle. An animal enthusiast and a raging foodie, experiencing life - one day at a time.



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