Strong cramps each time a newborn nurses are common in the first days after birth, and they usually mean the uterus is doing its job. Suckling releases oxytocin, a nine-amino-acid peptide hormone that pushes milk out and also makes the uterus contract as it shrinks back down. The American College of Obstetricians and Gynecologists (ACOG) says these “afterpains” are more common in people who have given birth before and during the first few days of breastfeeding. A heating pad and an over-the-counter pain reliever usually take the edge off; very heavy bleeding, a fever or severe pain that keeps building are reasons to call.
One hormone, two jobs
Oxytocin is made as part of a larger precursor protein, and the UniProt record for that precursor marks the short nine-residue oxytocin segment that is cut free. The hormone squeezes the muscle-like cells around the milk glands, which is the “let-down” reflex, and it also tightens the muscle of the uterus, which is why a synthetic version is used to start or strengthen labor.
A 2020 systematic review of oxytocin levels during breastfeeding pooled 29 small exploratory studies with 601 women. Breastfeeding set off an immediate oxytocin release lasting roughly 20 minutes, delivered in pulses in the early postpartum days, and levels were higher in women who had given birth before. That timing helps explain why the cramps tend to arrive with feeds rather than at random.
The squeezing has a purpose. A Cochrane review of pain relief for afterpains describes the cramping as the uterus contracting to reduce blood loss and return to its non-pregnant size.
Second and third babies often hurt more
In a 2003 study in the journal Pain, researchers asked 50 women about pain while breastfeeding in the three days after an uncomplicated vaginal birth and recorded uterine contractions in 30 of them. Nearly all, 96%, described deep pain during feeds, mostly in the lower abdomen, low back and breast. Pain intensity rose with the number of previous births, and so did the number and length of contractions; longer contractions went with higher pain scores. The study was small, but it fits ACOG’s description.
A much larger Swedish trial of 1,802 women, published in Birth in 2011, found afterpains were rated as more intense the day after birth than two hours after, again stronger in women with previous births. It also found that routinely giving synthetic oxytocin after delivery to help the placenta out did not make afterpains worse, a possibility that had been suggested but never tested.
What helps, and how strong the evidence is
ACOG’s postpartum pain guidance suggests a heating pad on the abdomen and says that for afterpains, ibuprofen may work better than acetaminophen. For people who are breastfeeding, ACOG calls ibuprofen the usual preferred first step because little of it passes into breast milk, and says acetaminophen is also safe. It advises talking with an ob-gyn before combining two or more pain medicines. Follow the label or your clinician’s directions, and check first if you have been told to avoid anti-inflammatory pain relievers.
The Cochrane review, updated in 2020, pooled 28 trials with 2,749 women after vaginal birth. Nonsteroidal anti-inflammatory drugs (NSAIDs) such as ibuprofen were probably better than placebo for adequate pain relief (moderate-certainty evidence) and probably better than opioids. Whether acetaminophen (paracetamol) beats placebo, or differs from NSAIDs, remained uncertain because the evidence was very low certainty. One important gap: 11 of the 28 trials excluded breastfeeding women, and none reported effects on breastfeeding or on babies, so the reviewers called for trials that include nursing parents.
When cramping is not just afterpains
Cramping and bleeding that slowly ease are expected. MedlinePlus notes that bleeding like a menstrual period can come and go for up to six weeks, along with menstrual-like cramps. ACOG lists warning signs that need prompt attention: call 911 or get emergency help for severe pain in the lower abdomen, chest pain or trouble breathing, and call your ob-gyn right away for a fever above 100.4 F, bleeding that soaks through two pads an hour for more than an hour or two, or vaginal discharge that smells bad.
The practical takeaway: if feeds bring a wave of period-like cramps in the first days, especially after a second or later baby, that is a normal oxytocin effect and a sign the uterus is contracting. Plan ahead with a heating pad and a breastfeeding-compatible pain reliever your clinician has okayed, and watch the bleeding and temperature rather than the cramps alone.
By The Everyday Brief · AI-assisted editorial. Drafted with AI research assistance; claims checked against the linked sources (fetched 2026-10-06 PT). Not medical advice.
Sources
- American College of Obstetricians and Gynecologists: Postpartum Pain Management
- Deussen AR, Ashwood P, Martis R, Stewart F, Grzeskowiak LE. Relief of pain due to uterine cramping/involution after birth. Cochrane Database of Systematic Reviews, 2020.
- Uvnäs Moberg K, et al. Maternal plasma levels of oxytocin during breastfeeding: a systematic review. PLoS One, 2020.
- Holdcroft A, et al. Pain and uterine contractions during breast feeding in the immediate post-partum period increase with parity. Pain, 2003.
- Jangsten E, et al. Afterpains: a comparison between active and expectant management of the third stage of labor. Birth, 2011.
- MedlinePlus (U.S. National Library of Medicine): Postpartum Care
- UniProt: Oxytocin-neurophysin 1 proprotein, including oxytocin (P01178)