Relaxin

Relaxin is a hormone that helps relax your ligaments, muscles and other tissues. Everyone has relaxin. But this hormone mainly helps with menstrual cycles and pregnancy.

Relaxin makes your body more flexible during pregnancy. This helps the growing fetus and prepares your body for vaginal delivery. But it can make you more prone to injuries and discomfort.

What does relaxin do?

Relaxin serves many reproductive roles. In males, it may help with sperm movement. In females, it helps manage menstrual cycles and pregnancy.

Once your ovaries release an egg during ovulation, relaxin levels rise to:

• Help relax the walls of your uterus to prevent contractions
• Prepare your uterine lining for implantation (when a fertilized egg attaches to your uterus, creating a pregnancy)

If pregnancy doesn’t happen, relaxin levels go down until the next time you ovulate. The levels stay high if pregnancy occurs. They continue to rise throughout the first trimester (the first 12 weeks) of pregnancy.

Relaxin functions during pregnancy

During pregnancy, relaxin:

• Helps grow the placenta
• Relaxes uterine muscles to help prevent preterm labor
• Loosens ligaments so your uterus can expand as the fetus grows
• Makes your abdominal muscles more flexible
• Relaxes blood vessels to adapt to increased blood volume
• Helps develop mammary glands, which make breast milk
• Softens and expands (dilates) your cervix before delivery
• Loosens your pelvis during childbirth

Between your growing belly and the loosening effect of relaxin, it’s common to feel unsteady. So, be extra mindful of your movements to reduce your risk of joint and muscle injuries.

Where does relaxin come from?

Relaxin comes from the:

• Ovaries in nonpregnant females
• Placenta in pregnant females
• Prostate in males

Researchers aren’t sure what triggers your body to release this hormone. It may control its own release or depend on other hormones, like luteinizing hormone (LH) or human chorionic gonadotropin (HCG).

There’s nothing you can do to change your relaxin levels.

When do you start making relaxin during pregnancy?

You make relaxin before pregnancy. Levels start to rise around ovulation and then soar if you become pregnant.

This hormone reaches its peak around the end of the first trimester. After that, it declines for the rest of your pregnancy before surging one last time just before delivery. Researchers believe the last surge helps relax your pelvis and open your cervix.

Can you have too much or too little relaxin?

Maybe. Researchers still have a lot to learn about the possible effects of high and low relaxin.

Certain studies suggest that high relaxin may cause prelabor rupture of membranes (PROM), when your water breaks before labor starts.

Low levels of relaxin may cause scleroderma, a condition in which your skin thickens and hardens. But there isn’t enough research to know for sure.

Healthcare providers don’t typically measure relaxin levels during pregnancy.

Can it cause pain?

It’s possible for relaxin to lead to pain. During pregnancy, relaxin loosens most of the muscles and ligaments around your pelvis, back and abdomen. This can make your joints feel less stable and lead to pain.

Relaxin may play a role in symphysis pubis dysfunction, which causes pain in your pelvis. You may feel pain when you use the stairs, get out of cars, change positions or stand on one leg.

Certain home remedies can help you manage this discomfort. For example, wearing a pregnancy support belt (belly band) can help stabilize your pelvis.