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Relaxin: what it is and why it's responsible for your pelvic pain

Relaxin is a hormone released by the ovaries and, during pregnancy, the placenta. As the name suggests, relaxin relaxes the body to support various other processes. That means you can thank relaxin for those achy hips during pregnancy but also that extra space in your pelvis to push baby out. A bit of a lose-win situation, really. ⁠

Now let’s dive into the specifics.

1. Relaxin peaks in the first trimester

Relaxin is thought to promote the growth of a healthy placenta and help your cardiovascular and renal systems adapt to the changing demands for oxygen and nutrients. And crucially, relaxin relaxes the muscles in the uterus to prevent unwanted contractions.⁠

2. Relaxin allows ligaments to stretch, affecting joints and muscles in pregnancy

This clever hormone relaxes the ligaments around the pelvic joints so that the pelvis can widen enough during the delivery of your baby. Sometimes this causes a feeling of instability and pain in the pelvic joints. Fun. ⁠

3. Relaxin softens the cervix and vagina ready for childbirth

Relaxin softens not only the ligaments in pregnancy but, towards the end, the cervix and vagina too. In fact, relaxin is also thought to promote a rupture in the membranes surrounding baby, kickstarting labour.⁠

4. Relaxin affects the non-pregnant too

The pain and inflammation associated with relaxin can unfortunately be felt even after pregnancy unless addressed. More generally, for women, relaxin levels rise around ovulation so that the uterus walls stay nice and relaxed and, once again, don’t start to contract. If no pregnancy occurs, then relaxin drops. And in men, relaxin is secreted from the prostate gland instead, and can be found in semen.⁠