A few minutes (sometimes a bit longer) after birth
separates from the wall of the uterus
and is delivered. This is why the placenta is commonly called the "afterbirth".
When a woman breastfeeds the hormone oxytocin is released and stimulates the contraction of uterine muscles. During the first few days after birth this contraction of the uterus helps to stop the bleeding caused by the detachment of the placenta from the wall of the uterus. Until the uterus returns to its pre-pregnancy size this contraction can be painful. The pain is worse if the uterus has been over distended (as in a multiple gestation) or if the woman has carried previous pregnancies. First time mothers may only notice a tightening or a menstrual cramp like sensation. Mothers of more than one child or of twins may feel this as a pain as strong as labor pain. This pain of the uterus contracting back to its normal size is called "afterbirth pain"
That same hormone, oxytocin, causes the milk-producing cells to contract and this moves milk from the back of the breast forward where it is more available to the infant. This is commonly called the let-down reflex or the milk ejection reflex or MER. Since this occurs from the same stimulation as afterbirth pains and since new mothers are often unaware of what the MER feels like but recognize the uterine cramping these 2 events can be verbally linked for her. If the mother knows her uterine cramping also means her milk is "flowing" it can be very reassuring.
However, even though they serve a good purpose, those cramps still HURT and it is good to know how to treat them and that they are temporary. They can be relieved with a heat pack over the uterus. If that is not enough many moms will take a pain medication. Depending on the severity of the pain this may be a NSAID or a narcotic. Moms also are reassured to know that the cramping sensation is temporary and goes away in a day or two as the uterus returns to its normal size. Even during a feeding the cramping stops as the uterus finishes tightening up again.
This uterine contraction serves a protective function. If breastfeeding does not occur other stimulations are needed to cause the uterus to contract or the mother may hemorrhage. A medication to simulate the normal hormonal milieu of lactation may be used or manual massage of the tummy
(and thereby the uterus) may be employed. Without breastfeeding more caution must be taken to prevent excessive bleeding as the uterus returns to a normal size.