Pumping breast milk leads to uterine contractions after giving birth. This is a normal and expected part of the body’s postpartum recovery. These contractions help the uterus return to its pre-pregnancy state.
The Hormonal Link
Nipple stimulation, whether from a baby suckling or a breast pump, triggers the release of oxytocin. This hormone is produced in the hypothalamus and stored in the posterior pituitary gland. Once stimulated, oxytocin is released into the bloodstream.
Oxytocin stimulates smooth muscle contractions. In the uterus, it binds to specific receptors on uterine muscle cells, leading to contractions. This mechanism is the same one responsible for contractions during labor. Beyond its role in uterine contraction, oxytocin also facilitates the milk ejection reflex, often called “let-down,” by causing muscle cells around the milk ducts to contract and release milk.
Uterine Involution and Afterpains
The contractions initiated by pumping are a central part of uterine involution, the process by which the uterus shrinks back to its pre-pregnancy size and position. After childbirth, the uterus is significantly enlarged, similar to the size of a grapefruit. Over approximately six weeks, it gradually reduces to about the size of a pear. These contractions help compress blood vessels at the site where the placenta was attached, which reduces postpartum bleeding.
The cramping sensations from these contractions are often called “afterpains.” Afterpains can feel similar to menstrual cramps, ranging from mild discomfort to more intense sensations. They are typically most noticeable in the first few days after delivery, often peaking around days two or three, and generally subside within a week to 10 days. Women who have had previous pregnancies often report more pronounced afterpains, as their uterine muscles may have less tone and need to work harder to contract. Experiencing these pains is a sign that the body is healing and recovering effectively.
Normalcy and Benefits
Uterine contractions during pumping or breastfeeding are a normal and beneficial response in the postpartum period. This process helps the body recover efficiently after childbirth. The contractions reduce the risk of postpartum hemorrhage by compressing blood vessels in the uterus.
These contractions also aid the uterus’s return to its non-pregnant state. While afterpains can be uncomfortable, their intensity typically lessens over the first few weeks postpartum, becoming less noticeable as the uterus continues to shrink.