As weird as it sounds, the answer is yes. This is made possible by hormones. When you breastfeed, your pituitary glands secretes a hormone called oxytocin. The function of this hormone is to contract smooth muscles, such as the milk sacs found in your breasts.
When the milk sacs contract, the milk moves to the front of the breast, making breastfeeding possible. Some mothers say that they feel it as a tingling feeling, which is called the “letdown” reflex.
The oxytocin does not only contract the smooth muscles in your breasts, but the smooth muscle cells in your uterus as well. It’s this contracting of the muscles that actually assist the uterus in shrinking to its original size.
The uterus of non-breastfeeding mothers will never shrink back. It will always remain slightly enlarged (Chua S, Arulkumaran S, Lim I et al. "Influence of breastfeeding and nipple stimulation on postpartum uterine activity." Br J Obstet Gynaecol 1994; 101:804-805)
All women differ from each other. Some women have faster metabolisms’ than others, whilst other women have a non existing metabolism. So let’s talk about the average time it takes for your uterus to get back to normal.
Doctors say that after birth your uterus shrinks back to the level of your belly button. It’s believed that about two days after birth, your uterus is about the size it was at your 18th week of pregnancy. This is why some mothers still look pregnant.
After one week after birth, it will be the size it was at 12 weeks of pregnancy. At about six to ten weeks, it will be back to its original size (as big as a closed fist).
After giving birth, it’s important to deliver
the placenta as well. After the placenta has been delivered, your womb should
contract strongly, to shut of the blood vessels it was attached to.
Excessive bleeding can cause severe drop in blood pressure and may even lead to shock or death, if not treated.
When you then breastfeed after birth, the hormone oxytocin promotes contractions in your uterus, so that the open blood vessels close quicker. Some doctors even massage your uterus to give you a synthetic form of this hormone.
Breastfeeding also lowers the risk of ovarian cancer and premenopausal breast cancer and even osteoporosis.
Breastfeeding does not only benefit your baby, but you too!
Some extra reading on the subject...
A Well-Kept Secret - Breastfeeding's Benefits to Mothers