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Let’s Relax about… Relaxin

Perhaps the first thing to emphasise about Relaxin is that it is a woman’s friend. No hormone is produced by the body without a helpful purpose and in harmony with other amazing processes. Yes there’s a delicate balance that can often go wrong, but that’s usually down to external factors rather than a faulty blueprint.

To make us vulnerable by ‘loosening ligaments’ or ‘weakening connective tissue’ strikes me as counter-productive in such an otherwise astounding process of pregnancy and motherhood. I tend to park such comments in the same meaningless pile as ‘wear and tear’, preferring a little mystery and motivation to learn instead of these damning diagnoses.

As is often the case, what the literature tells us and what it doesn’t tell us can be equally valuable. There appears to be no correlation between pain levels and laxity of joints, while fear and beliefs are streaking ahead as causative factors. We are limited by a lack of research in some areas, for example ‘what if a woman has too much Relaxin?’, but it seems, quite rightly, that establishing its role in a normal population is required before defining what ‘too much’ even is anyway.

So what does Relaxin actually do?

Part of our monthly cycle during reproductive years (yes, we all produce it, every month!), Relaxin increases after ovulation, relaxing the walls of the uterus in preparation for pregnancy. When a pregnancy fails to occur, just like Oestrogen it wanes again towards the monthly menses.

Other research has shown that aside from its reproductive role, Relaxin plays a part in the promotion of tissue healing, remodelling and reducing fibrosis. This is obviously useful at any point in life, and also seems perfectly targeted at those difficult days post-labour, when baby is demanding nutrients and depleting shut-eye, and the body may have gone through some significant trauma in the labour suite. Despite all our other distractions, our body quietly sets to work with this gorgeous hormone gently knitting us back together.

During pregnancy, Relaxin is actually highest in the First Trimester. It appears to help regulate blood pressure by increasing vasodilation – perhaps playing a part in the pregnancy ‘glow’ and of course helping the body to adapt to the demands of the growing foetus. It also ensures that its brief monthly role gets extended, inhibiting contractions of the uterus thus reducing the chances of early delivery or miscarriage.

Towards labour is where it seems to have gained its fifteen minutes of fame: it is generally accepted that Relaxin eases the pelvic ligaments to allow for childbirth. However, Relaxin is not a one-size fits all: it is unsurprisingly targeted at reproductive tissue, and like all other hormones has specific receptors: it is not running rampant throughout all our bodily ligaments.

Typically it is the pubic symphysis that is targeted. There’s not much mention of other specific ligaments of the pelvis, so I would argue that we shouldn’t lump them all together unless told otherwise. During labour, it is the symphysis that would allow ease of passage for the baby, perhaps another reason for it being the only pelvic joint with a disc. The sacral area provides a firm wall against which the uterus and pelvic floor can move and guide the baby out – so it wouldn’t make sense for this to become ‘lax’ at the crucial moment. Yes the easing of the symphysis can cause longer term discomfort, but this is likely far more the result of birthing positions, muscle imbalance or straining than a lowly hormone just doing its job.

The whole pelvis is under increasing load at this time, so perhaps it’s worth considering that Relaxin might not be the only cause of pelvic girdle pain – in fact the literature is very conflicted on this issue. From assessing a woman’s musculoskeletal situation, there are usually plenty of other factors that are likely to contribute: tight adductors, weak abductors, lumbar mobility just for starters. Consider the tension and altered loading on the pubis symphysis, simply by a change in posture and the sheer number of muscles that attach there (at least 13). To tell our patients confidently that it’s Relaxin causing their PGP is simply not evidence based.

Post natally it somehow has developed notoriety. PGP does often disappear after labour as the extra load has finally ceased, so in those whose pain continues Relaxin seems to be caught with the smoking gun. Relaxin is known to perpetuate during breastfeeding, but again this makes sense in helping the body, not harming it. Its role in calming inflammation, healing damaged tissue during a time of high stress and change, and reducing fibrosis are all good reasons to keep baby on the boob. Even if Relaxin did play a role in initiating PGP, for a specific purpose targeting specific cells, it will almost certainly not be the perpetuating factor, considering how all the muscles have been adapting and compensating for nine months. As we know (and have experienced) muscles don’t just spring back to full health once the load has been removed or the trauma is over. Is anything in a human body ever that straightforward?

It’s the getting back to fitness that seems to be the sticking point for women. We all seem to acknowledge that it’s ‘society’ telling us to spring back to washboard stomachs and half marathon distances, to reject our maternal urges and get time back for ourselves. Yet the medically minded can tend to turn the blame onto our internal functions, making us feel worse instead. Research does show a connection to ACL injury, especially mid-cycle (i.e. post ovulation, when oestrogen is also high). However, such research, like all other research, needs more investigation, and in vitro studies on college-level athletes perhaps doesn’t translate across seamlessly to new mums. We also know that monthly hormones play a part in worsened prolapse or urinary incontinence symptoms at a certain time in the cycle. Are they the cause, or just doing their thing under difficult circumstances?

I would argue the latter. Childbirth, child rearing, expectations of recovery and even sport have changed exponentially in just a few generations. We are still human animals, doing our best to adapt to the environment. Our hormones do a grand job, are up against a great deal of challenge in the modern world, and their cries are largely ignored, despite often debilitating symptoms of imbalance. I, perhaps cynically, think that if Relaxin was truly the problem, some Pharma company would have jumped on some expensive hormone therapy and pedalled it as essential for the recovery for new mums by now.

In the absence of specific wisdom on this elusive hormone, and in the presence of information that paints Relaxin as just another nurturing wonder of chemistry, I think our duty is to tackle the real causes of pain – catastrophisation and negative beliefs – in our patients, rather than exacerbate them. It’s ok to not know the answer: that’s the joy of discovery and exploration. But let’s make the journey full of wonder, not fear.

As Frankie says… Relax…