The hormone relaxin

First, a little background.

During pregnancy, as you probably know, the body undergoes significant hormonal changes. There are seven hormones that are primarily responsible for ensuring a healthy pregnancy and a successful birth. These are human chorionic gonadotropin (hCG), estrogen, progesterone, relaxin, human placental lactogen (hPL), prolactin and oxytocin (2).

Each of these hormones has an important role during pregnancy, but the one we are focusing on today is relaxin. 

If you are pregnant or have been in the past, you may have heard of relaxin, a hormone that has been known, hence its name, to relax connective tissue and ligaments, such as those in the pelvis, in preparation for childbirth. 

BUT - is this really the case? Let’s investigate.

Schauberger et al (1996) conducted a study that looked at whether or not joint laxity correlated with levels of relaxin. Interestingly, although there was a significant increase in joint laxity over the course of pregnancy and postpartum, none of these actually correlated with serum relaxin levels.

Kristiansson et al (1996) conducted a study to look at back pain during pregnancy and whether this correlated with the relaxin hormone. They found that relaxin peaks at 12 weeks of pregnancy and reduces back down to 50% of this level by 17 weeks.

https://www.inne.io/en/blog/article/hormonal-changes-during-pregnancy/

So what does this mean?

The results of these studies indicate that relaxin may not actually be the hormone involved in softening of ligaments in preparation for childbirth. The literature so far has not determined which hormone may be responsible for this but it is clear that joint laxity increases as pregnancy progresses. It also seems that there may be a relationship between this hormone and the development of pelvic pain in women. 

What we do know about relaxin

Relaxin is a hormone produced by your ovaries and later by the placenta during pregnancy. It is responsible for preparation of the uterine lining essential for embryonic growth and levels too high or low may be associated with fetal loss. It is responsible for relaxation of smooth muscle.

Where to from here?

While we wait for science to tell us more, we know that the involvement of women’s health physiotherapists in the care of pregnant women is extremely important, particularly in the prevention of conditions caused by pregnancy hormones and the huge changes that a woman’s body undergoes during this time.

Participating in a physiotherapist designed exercise and education program, like our Strong Mama Program, will help keep you strong during your pregnancy, help avoid injury and will assist with an empowered postnatal recovery. We guide you week by week.

References:

Hormone Health Network, Glands & Hormones A-Z

Kristiansson et al, Back pain during pregnancy: a prospective study, Spine, 1996

Olivia, B. & Nadia, B., Frontiers in Endocrinology, Hormonal Changes Associated With Intra-Uterine Growth Restriction: Impact on the Developing Brain and Future Neurodevelopment, 2019, 

Pratap, K. & Navneet. M.,  Hormones in pregnancy, Journal of the Nigerian Medical Association,  2012, 53(4):, page 179–183

Schauberger et al, Peripheral joint laxity increases in pregnancy but does not correlate with serum relaxin levels,Am J Obstet Gynecol, 1996