The relaxin hormone is produced during pregnancy to help you "relax" and prepares the body for childbirth during the latter stages of pregnancy.

During the reproduction process, levels of the relaxin hormone will increase to help get the uterus ready for the possibility of pregnancy.

This happens after ovulation. Levels will slowly decrease if conception does not happen. 

During the early stages of pregnancy, relaxin will restrain the effects of contractions in the uterus wall. Doing so helps prevent premature birth. Relaxin also aids in regulating both the renal and cardiovascular systems. This is needed to cope with the extra demand placed on the body by the baby foetus for oxygen and nutrients. Relaxin will be at its highest level during the first trimester of pregnancy. This is needed to help promote the development of the foetus and placenta.

As you reach the end of your pregnancy journey, the relaxin hormone will stimulate membranes around the foetus which allows for the opening of the cervix (known as water breaking) this prepares the body for childbirth. There is also further evidence that relaxin soothes ligaments, muscles and bones in the pelvis as you get closer to the big day. The levels of relaxin are much lower during this stage of pregnancy, however, the hormone is still just as important. 

You'll start to notice your balance becomes a little "off" as you reach the later stages of pregnancy. This is down to relaxin loosening ligaments and muscles. So don't be alarmed if you start to have trouble with keeping a steady balance, just be cautious and take extra care when walking around.

You won't feel any major side effects from relaxin during pregnancy. However, it's estimated that 1 in 300 pregnancies will suffer from symphysis pubis dysfunction (SPD) - A very painful stiffness to the pelvic joints.

Lower back pain

Find it hard to walk both up and down stairs

Pain in the middle of the pelvis

Pain when changing sleep positions

Wearing a support band can really help those who may be suffering from extreme back pain in the spine area during pregnancy. This is caused by relaxin excessively loosening the spine. 

You'll find that relaxin is the most dominant during the second half of your menstrual cycle - the phase where levels increase due to the possibility of pregnancy.

If you find that you do become pregnant, the hormone will now serve a whole new purpose. It will pair with other hormones to help support the early stages of pregnancy. Then as you journey through the 9 months of pregnancy and eventually to delivery, the relaxin hormone will start to loosen joints, muscles, ligaments and bones to make childbirth and labour easier. If you feel any extreme pelvic pain during pregnancy, then make sure to contact your doctor immediately. 

Further reading : 
National Library of Medicine : https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3856209/