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Transformers & Miracle Workers – How Your Body Changes in Pregnancy

Birth Preparation

Image by Melissa Jean (@melissajeanbabies)

Pregnancy is about more than just growing a baby.
Sure, technically that’s what it’s about, but for your body it means so much more.

Every single system of your body needs to change in some way to keep you and your baby healthy. Seems drastic, maybe, but growing new humans is a pretty drastic undertaking, wouldn’t you say?

There are of course a thousand different changes your body goes through during pregnancy, but here are 5 systems and the fascinating ways your body adapts them for pregnancy and to prepare for birth.

Happy reading!

Heart and blood

By the end of pregnancy your body has increased your blood volume (the amount of blood circulating in your system) by around 40%. This is partly because your growing uterus and your placenta place a bigger demand on your circulation. However, it is also your body’s way of equipping you to deal with blood loss at birth. Within your blood there are changes too. Each red blood cell has an increased ability to carry oxygen around the body, which means the job gets done more efficiently. Your blood also becomes better at clotting (pregnant women are in what is known as a ‘hypercoagulable state’). This is also to equip you for birth. By the third trimester of pregnancy, your body pumps 600-800mL of blood to your placenta. After your baby is born, your placenta separates from the wall of the uterus. Your blood has to work quickly to stop the blood flow once this happens, otherwise your blood will be pumped into an empty uterus and you will lose that blood out of your circulation. Due to these amazing changes in your blood, this happens much faster than it would otherwise! All these changes would ordinarily put more stress on your system, altering your blood pressure and your heart rate. But your body is prepared for this too, and by expanding your blood vessels these changes are kept surprisingly minimal.


As your baby takes up more and more room in your abdomen as your pregnancy progresses, your other organs are pushed around to accommodate for it. The lungs are one of the organs affected by this! Your diaphragm that normally allows your lungs to expand and contract is raised by several centimetres into your chest cavity. Ordinarily this would mean that your lungs have less room to expand and therefore you have less lung capacity and need to breathe faster to make up for it, but (you guessed it), your body is ready with an answer for this. Your rib cage becomes more flexible, which widens the overall diameter and circumference of your chest. This allows your lungs to expand outwards to make up for the space they lose vertically. You may notice you become more of a ‘chest breather’ in pregnancy rather than an abdominal breather. Overall, your lung capacity and breathing rate are mostly unchanged during pregnancy – cool hey!


You may normally think of your pelvis as one fixed bone (or maybe you’ve never given it much thought at all, which is okay too!), however it is several bones that are held in place by some normally fairly rigid joints. During pregnancy though a hormone called ‘relaxin’ will )shockingly) relax those joints, making them more flexible. This causes the ‘waddling’ gait that pregnant women develop during pregnancy, but more than this, it actually serves a very important purpose. Increased mobility of the joints allows the pelvis to shift as needed as the baby makes its way through the pelvis during labour!


Many of these changes may have been obvious to you already if you are pregnant or have been before, but did you ever wonder why? Breasts often get larger during pregnancy, but it is more than just ‘bigger’. The tissue in the breast itself is changing! During pregnancy you actually often have a reduction in fatty tissue, but an increase in the breast tissue and structures required for producing breastmilk. Your breasts also develop more receptors to prolactin (the hormone responsible for milk supply), ready for milk production to begin. Your colostrum production begins around week 18 of pregnancy, which you may notice leaking (although not everyone will leak). Perhaps the most obvious sign, however is that your nipple often enlarges and maybe changes shape, and your areola also darkens and gets bigger. This is for a super cool reason. When babies are born they are quite short sighted, and their vision isn’t great. They see best with dramatic colour distinctions. For most women, a darkened areola creates a much more noticeable difference between it and the surrounding breast, almost like a target or a flashing sign for your baby to see and make their way towards once they are born!


Finally your uterus, which really is one of the main stars of the pregnancy show. Before pregnancy, our uterus’ are ‘pelvic organs’ – little pear-sized things nestled within our pelvis weighing roughly 50g. By full term, however, your uterus will reach to the bottom of your sternum and have about 1kg of muscle bulk, which is a 20 times increase in weight! That muscle also develops receptors on its surface to hormones, including oxytocin, that will create your labour and birth your baby. Possibly even more incredibly, your uterus will slowly return basically to its original size in the first few weeks after birth. Immediately after your placenta is born, your uterus will be below your belly button, and by two weeks postpartum it will be back within your pelvis again.   So, if it has not amazed you lately that women are capable of growing babies within their own bodies, I hope this blog post brings that wonder back to you. How incredible is it that our bodies are able to morph themselves into a being that can sustain two lives, then shift back when the time is right? Our bodies really do deserve the utmost respect from us because of what they are capable of. Say thank you to your body today!

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