Relaxin: Hormone, Pregnancy Effects, Pelvic Pain and Care
Updated: 3 days ago
Medically reviewed by Dr. Baraa Alnahhal, MD · Last reviewed: October 2026
Quick Answer: What does relaxin do?
Relaxin is a hormone that loosens muscles, ligaments and joints. It rises around ovulation and during pregnancy, when it helps the uterus and uterine lining prepare for implantation, supports placental development, helps the body stretch, relaxes the pelvis and cervix before delivery and may prevent early uterine contractions. [1]
Core idea | Plain-language meaning |
Main sources | The ovaries produce relaxin; the placenta also produces it during pregnancy. |
Menstrual-cycle pattern | Levels rise after ovulation, when the ovaries release an egg. |
Early pregnancy | Levels remain high and rise through the first trimester. |
Peak | Levels peak around the end of the first trimester. |
Delivery preparation | It helps relax the pelvis and prepare the cervix for labor and delivery. |
Body effects | Looser joints and ligaments can increase flexibility but may also increase unsteadiness or injury susceptibility. |
Pain link | It may be associated with pregnancy-related pelvic girdle pain. |
After birth | Joints and ligaments can stay looser for months; pelvic girdle pain eases within four months for most women but persists in about 1 in 5. |
What the research says
Relaxin has been linked to pubic symphysis separation around birth, but the evidence is small. In a cross-sectional study of 54 women (15 with peripartum pubic symphysis separation and 39 without), serum relaxin measured one day after delivery (OR 1.022) and neonatal weight (OR 1.002) were associated with the occurrence of separation, but not with its severity (Wang et al., World J Clin Cases, 2021). [2]
Exercise in pregnancy lowers pain severity but not the odds of pelvic or back pain. A systematic review and meta-analysis of 32 studies including 52,297 pregnant women found that prenatal exercise did not reduce the odds of low back, pelvic girdle or lumbopelvic pain, but 15 randomized trials showed lower pain severity in women who exercised (standardized mean difference −1.03, 95% CI −1.58 to −0.48). The quality of evidence ranged from very low to moderate (Davenport et al., Br J Sports Med, 2019). [3]
Stand-alone exercise may help prevent episodes of low back pain in pregnancy. A meta-analysis of six randomized trials with 2,231 participants found moderate-quality evidence that stand-alone exercise prevents episodes of low back pain in the long term (RR 0.92, 95% CI 0.85–0.99), while other prevention strategies lacked good-quality evidence of benefit (Santos et al., Physiotherapy, 2023). [4]
What is relaxin?
Relaxin is a reproductive hormone with an important role in the reproductive system, particularly during pregnancy. Its main effect is to relax muscles and ligaments and make them more flexible. [1]
The body also produces relaxin during the menstrual cycle. Its roles include relaxing the uterus, preparing the uterine lining for implantation and preventing contractions. [1]
Where does relaxin come from?
The ovaries release relaxin after ovulation. If conception occurs, the placenta also begins to secrete it. [1]
It is not certain what causes the body to release relaxin. Its release may be self-controlled or may depend on other hormones such as luteinizing hormone or human chorionic gonadotropin. [1]
How does relaxin change during the menstrual cycle?
Relaxin levels begin to rise around ovulation, when the ovaries release an egg. [1]
If conception does not occur, relaxin levels decrease until the next cycle. If conception occurs, levels stay high and continue rising through the first trimester. [1]
What does relaxin do during pregnancy?
During pregnancy, relaxin helps the body stretch as the fetus grows. It relaxes the muscles, ligaments and joints of the pelvis and helps prepare the body for labor and delivery. [1]
Pregnancy function | Description |
Implantation | Helps prepare the uterine lining for implantation. |
Placenta | Helps the placenta grow if implantation occurs. |
Uterine muscle | Helps prevent early contractions and preterm labor by relaxing uterine muscle. |
Expanding uterus | Relaxes ligaments so the uterus can expand. |
Abdominal wall | Makes abdominal muscles more flexible. |
Blood vessels | Relaxes blood vessels to accommodate increased blood volume. |
Pelvis | Helps relax the pelvis before delivery. |
Cervix | Helps the cervix soften and expand before labor and delivery. |
Birth process | Helps the pelvis relax so the baby can descend the birth canal. |
When does relaxin peak in pregnancy?
Relaxin production rises substantially if pregnancy occurs and reaches its peak around the end of the first trimester. [1]
After the first-trimester peak, relaxin declines for the rest of pregnancy before surging again just before delivery. Researchers believe the final surge helps relax the pelvis and widen the cervix. [1]
Can relaxin affect the rest of the body?
Laboratory and clinical research describes other effects of relaxin, including widening blood vessels, reducing scarring (fibrosis) and inflammation, and helping new blood vessels grow, in both women and men. These are research findings, not established self-directed treatments.
Relaxin also makes joints, ligaments and muscles looser during pregnancy. This can increase flexibility, but it may also raise the risk of joint and muscle injuries and may contribute to feeling unsteady. [1]
What does relaxin feel like?
You cannot feel relaxin itself, but it can lead to pain. By loosening the muscles and ligaments around the pelvis, back and abdomen, it can make joints feel less stable. [1]
The combination of a growing belly and the loosening effect of relaxin can make unsteadiness more common. [1]
What is pregnancy-related pelvic girdle pain?
Relaxin may play a role in pregnancy-related pelvic girdle pain, including symphysis pubis dysfunction, which causes pain at the front of the pelvis. It may hurt when using stairs, getting out of a car, changing positions or standing on one leg. [1]
Pain may be felt at the front of the pelvis over the pubic symphysis (see our guide to the pubic symphysis), in one or both sacroiliac joints at the back of the pelvis, in the lower back or in the buttock area.
Relaxin loosens many of the muscles and ligaments around the pelvis, back and abdomen, which can make joints feel less stable. A pregnancy support belt (belly band) can help stabilize the pelvis. [1]
Can you have too much or too little relaxin?
Possibly. Researchers still have a lot to learn about the effects of high and low relaxin. [1]
Some studies suggest high relaxin may cause prelabor rupture of membranes (PROM), when the water breaks before labor starts. Low levels of relaxin may be linked to scleroderma, a condition in which the skin thickens and hardens. More research is needed in both cases. [1]
Question | What can be said cautiously |
Can relaxin be high or low? | Yes, but the effects are not well understood. |
Is high relaxin linked to early water breaking? | Some studies suggest high levels may cause prelabor rupture of membranes (PROM), but more research is needed. |
Does low relaxin cause scleroderma? | Some studies have suggested a link, but the evidence is not sufficient to establish causation. |
Is relaxin usually tested in pregnancy? | No. Healthcare providers don't typically measure relaxin levels during pregnancy. |
Can you change your relaxin levels? | No. There is nothing you can do to change your relaxin levels. |
How long does relaxin remain after delivery?
Joints and ligaments can stay looser for a while after birth. One review reports that knee ligament stability may not have fully recovered by four months after delivery. Pelvic girdle pain resolves within four months for most women but persists in about 1 in 5.
Because ligaments and joints may remain loose, extra care with exercise after delivery makes sense. This timeline varies and should not be used to decide whether a symptom is normal or whether exercise is safe for a particular person. Ask a healthcare professional for individualized advice.
How can you move safely when relaxin is high?
Extra care is recommended during pregnancy because relaxin can increase flexibility and unsteadiness. Being mindful of your movements can lower the risk of joint and muscle injuries. [1]
A pregnancy support belt (belly band) can help stabilize the pelvis during pregnancy. It is not a substitute for an evaluation of significant or persistent pain. [1]
When should pregnancy-related pelvic pain be discussed?
Talk to a healthcare professional if you experience pelvic pain during pregnancy. Pain can occur at the front of the pelvis, in the sacroiliac joints, in the lower back or in the buttock area, and professional assessment can help determine whether it is pregnancy-related pelvic girdle pain or another problem.
Do not use relaxin as a self-diagnosis. New, severe, persistent or worsening pain, bleeding, fluid leakage, regular contractions, fever, fainting, severe headache, vision changes or reduced fetal movement should be assessed promptly by the appropriate pregnancy-care professional.
What questions should you ask a healthcare professional about relaxin?
Question | Why it helps |
Could my pain be pregnancy-related pelvic girdle pain? | Relaxin may play a role in pelvic pain during pregnancy. |
Which movements should I avoid? | Relaxin can raise the risk of joint and muscle injuries, so movement choices matter. |
Would a support belt help me? | A pregnancy support belt can help stabilize the pelvis. |
Could another condition explain my symptoms? | Relaxin does not diagnose a condition. |
How should I return to exercise after birth? | Joints and ligaments may take months to regain full stability. |
How long might pelvic pain last after birth? | It resolves within four months for most women but persists in about 1 in 5. |
Conclusion: Relaxin supports change, but symptoms still deserve context
Relaxin is a reproductive hormone made by the ovaries and, during pregnancy, the placenta. It relaxes muscles, joints and ligaments and helps the uterus, pelvis and cervix prepare for pregnancy and delivery. [1]
Its levels rise after ovulation, stay high and rise in early pregnancy, peak around the end of the first trimester, decline later and surge again before delivery. Most people do not feel relaxin itself, but its effects can contribute to unsteadiness, looser joints and pregnancy-related pelvic girdle pain. High and low levels remain areas of incomplete research. [1]
Use this guide to prepare questions for a qualified pregnancy-care professional. It is an educational resource, not a diagnosis or a substitute for individualized care. [1]
Frequently Asked Questions
What is relaxin?
Relaxin is a reproductive hormone produced by the ovaries and, during pregnancy, the placenta. It relaxes muscles, ligaments and joints.
What is the main function of relaxin?
Relaxin's main function is to relax muscles and ligaments and make them more flexible. During pregnancy, it helps the body stretch and prepare for delivery.
When does relaxin rise during the menstrual cycle?
Relaxin levels rise after ovulation, when the ovaries release an egg. If conception does not occur, levels decrease until the next cycle.
When does relaxin peak in pregnancy?
Relaxin levels peak around the end of the first trimester, decline for the rest of pregnancy and surge again just before delivery.
What does relaxin do during pregnancy?
Relaxin helps prepare the uterine lining for implantation, may help the placenta grow, relaxes the uterus, pelvis and blood vessels, and helps the cervix soften before labor.
Can you feel relaxin?
You cannot feel relaxin itself, but by loosening joints and ligaments it can lead to pelvic pain and unsteadiness.
Can relaxin cause pelvic pain?
Relaxin may play a role in pregnancy-related pelvic girdle pain, which can affect the front of the pelvis, the sacroiliac joints, the lower back or the buttock area.
Can relaxin make you unsteady or prone to injury?
Looser joints and ligaments can increase flexibility but may also contribute to unsteadiness and a higher risk of joint and muscle injuries.
How long does relaxin stay after delivery?
Joints and ligaments can stay looser for months after birth. Pelvic girdle pain resolves within four months for most women but persists in about 1 in 5.
Is relaxin usually tested in pregnancy?
No. Healthcare providers don't typically measure relaxin levels during pregnancy. Possible links between relaxin levels and prelabor rupture of membranes or scleroderma are still being studied.
Related guides
References
Cleveland Clinic. Relaxin: Hormone Production In Pregnancy & Function. Cleveland Clinic. Updated October 28, 2026. https://my.clevelandclinic.org/health/body/24305-relaxin
Wang Y, Li YQ, Tian MR, et al. Role of relaxin in diastasis of the pubic symphysis peripartum. World J Clin Cases. 2021;9(1):91-101. PMID 33511175. https://doi.org/10.12998/wjcc.v9.i1.91
Davenport MH, Marchand AA, Mottola MF, et al. Exercise for the prevention and treatment of low back, pelvic girdle and lumbopelvic pain during pregnancy: a systematic review and meta-analysis. Br J Sports Med. 2019;53(2):90-98. PMID 30337344. https://doi.org/10.1136/bjsports-2018-099400
Santos FF, Lourenço BM, Souza MB, et al. Prevention of low back and pelvic girdle pain during pregnancy: a systematic review and meta-analysis of randomised controlled trials with GRADE recommendations. Physiotherapy. 2023;118:1-11. PMID 36288631. https://doi.org/10.1016/j.physio.2022.09.004
Fiani B, Sekhon M, Doan T, et al. Sacroiliac Joint and Pelvic Dysfunction Due to Symphysiolysis in Postpartum Women. Cureus. 2021;13(10):e18619. PMID 34786225. https://doi.org/10.7759/cureus.18619
Yalçınkaya B, Sezgin EA, Saçıntı KG, et al. Neuromusculoskeletal disorders in pregnancy revisited: Insights and clinical implications. Jt Dis Relat Surg. 2025;36(3):741-750. PMID 40784007. https://doi.org/10.52312/jdrs.2025.2242
Sarwar M, Du XJ, Dschietzig TB, et al. The actions of relaxin on the human cardiovascular system. Br J Pharmacol. 2017;174(10):933-949. PMID 27239943. https://doi.org/10.1111/bph.13523 Erratum in: Br J Pharmacol. 2017;174(24):4836. PMID 29235105. https://doi.org/10.1111/bph.14111
Medical disclaimer
This article is for general educational purposes and is not a substitute for professional medical advice, diagnosis or treatment. Always seek the advice of a qualified healthcare professional with any questions about a medical condition or treatment.
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