Uterine involution is defined as the process by which the uterus returns to its pre-pregnancy size and shape. This begins soon after delivery, around 6-10 days postpartum, and may take several weeks or months to complete. It is an important part of the puerperium and consequently the post-birth healing process.
Involution is brought about by the combined actions of the myometrium, which contracts and shortens the muscle fibers; and by the cervix and vagina, which contract and shorten the ligaments and muscles. The cervix and vagina also contract, pushing the mucous plug and the blood vessels that supplied the placenta with oxygen and nutrients into the vagina. The perimetrium (the serous membrane that covers the uterus) also contracts and helps to reduce the size of the uterus. All these are hormone-dictated. Finally, as the uterus shrinks, it pulls on the ligaments and muscles that hold it in place, which causes them to shorten.
The hormone that initiates and controls uterine involution is oxytocin. Oxytocin is produced in the hypothalamus and released into the bloodstream by the posterior pituitary gland which in turn stimulates the myometrium.
Uterine Involution vs. Other Terms
Uterine involution is often confused with another term – uterine deflation. Uterine involution and uterine deflation are two separate processes. Uterine deflation is the process by which the uterus releases all of the fluid that is accumulated during pregnancy. This usually occurs within 24 hours after delivery.
There are several other terms that are often confused with uterine involution, including postpartum bleeding and lochia. Postpartum bleeding is the normal bleeding that occurs after delivery, which typically lasts for up to two weeks. Lochia is the discharge that results from the healing process of the uterus, and it may last for up to six weeks.
It is important to note that uterine involution, uterine deflation, postpartum bleeding, and lochia are all normal processes that occur after childbirth. If you are experiencing any unusual symptoms, please consult with your healthcare provider.
This image shows how often the term ‘Uterine Involution’ is used in relation to other, similar birth terms:
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