As soon as the egg and sperm cell meet, these chemical messengers fire up to ensure that the right things happen at the right time.
There are unpleasant side effects: Your emotions seesaw, there’s a furnace in your chest and those pimples you last saw as a teen are back.
But there are also lovely surprises: those two peanuts you smuggled under your shirt before are now proper boobs bursting out of your bra.
All these changes are the result of more than 30 hormones coursing through your body. We look at a few.
Human placental lactogen (hCG)
The pregnancy alarm
One of the first hormones to arrive has the intimidatingly long name of human chorionic gonadotropin (hCG), but it’s also known as the pregnancy hormone. This hormone is only present during pregnancy, so it’s used for pregnancy tests.
It occurs in your blood and urine. So whether you use a home pregnancy test or get a doctor to take blood – if there’s hCG, you’re pregnant! Just a few days after the fertilised egg has burrowed into the uterine lining, the brand-new placenta starts producing hCG.
The amount of hCG increases incredibly quickly and reaches a peak at day seventy. Thereafter, the level decreases, and the hormone then keeps a low profile for the rest of your pregnancy.
The most important function of hCG is to ensure that the steroid hormones oestrogen and progesterone continue to be produced. Without hCG, your progesterone level will decrease again and you’ll menstruate.
As the placenta becomes more mature and can take over the production of oestrogen and progesterone itself, hCG production decreases.
If you’re looking to blame something for that morning sickness and the immense fatigue that hits you in the first trimester, try hCG.
It’s also the hormone that’s responsible for sending you off to the loo every five minutes, and it suppresses your immune system to lower the risk of your body rejecting the baby – which makes you more susceptible to illness during this time.
Better blood flow and sore boobs
Oestrogen is perhaps the most well known female hormone and is produced throughout your pregnancy. As your pregnancy progresses, more and more oestrogen pumps through your body.
This group of hormones is usually produced in the ovaries, but during pregnancy, it’s also made in the placenta, and it plays a key role in a healthy pregnancy.
It aids blood flow to the uterus, supports womb growth and maintains the uterine lining – all to ensure an ideal environment for your baby to grow.
Oestrogen helps to improve blood circulation and also ensures that your blood volume starts increasing by week ten. Plus, it activates and regulates the production of other key hormones, including progesterone.
The baby also benefits from oestrogen:
It helps his organs develop, and later on it’s partially responsible for the development of female sex characteristics. It also regulates the bone density in baby’s developing arms and legs.
It’s oestrogen, together with other hormones, that causes your boobs to swell and become sore or tender early in your pregnancy and start swelling later on – all in preparation for breastfeeding.
And while oestrogen is busy with so many important tasks, it unfortunately also has a few less pleasant side effects, like the permanently blocked nose you sometimes have during pregnancy, and even headache and postnasal drip.
The extra blood can also make your skin look red and blotchy and cause your palms to itch. Feel free to blame the oestrogen (together with a few other hormones) for the pigmentation that’s appearing all over: darker nipples, a brown stripe on your belly sometimes and dark marks around your eyes.
Keeps baby inside
Progesterone also becomes very important while you’re pregnant, as it prevents your uterus spontaneously aborting the foetus by developing a “lining” that can support the placenta.
This, in turn, is very important for the baby’s supply of food and oxygen. Initially, the ovaries produce progesterone, but from the second trimester, the placenta also makes it.
Before your pregnancy your uterus contracts and moves naturally, but while you’re expecting, progesterone helps to prevent these movements. It helps your uterus swell and makes space for your growing baby.
MUST READ | Yes, I'm pregnant, but why am I so tired?
As your pregnancy progresses, your progesterone level increases – until just before birth, when it decreases to give the womb a chance to contract.
Progesterone stimulates the growth of breast tissue and is responsible, together with oestrogen, for the tenderness in your boobs early in pregnancy. And yes, progesterone is not all good: All the progesterone in your body conspires with the hormone relaxin to influence the smooth muscles.
That’s why the valve between your tummy and throat doesn’t always work very well and so you may experience heartburn, especially in the third trimester.
Progesterone and relaxin can also soften cartilage, which loosens joints and ligaments and causes all kinds of hip and pelvis problems. Besides, it also relaxes the digestive system and bladder, which can lead to constipation and flatulence.
It can make your gums bleed and give you acne again for the first time after your teenage years. And it can make you sweat more than usual!
Prolactin is responsible for the multiplication of milk-producing cells in your breasts.
While you’re pregnant, progesterone and oestrogen prevent milk production, but as soon as baby’s born, the levels of these hormones drop dramatically, and the dairy can start producing thanks to prolactin.
Prolactin increases gradually as your pregnancy progresses, and the increased oestrogen in your body is believed to be responsible.
Later on, prolactin helps to keep you from falling pregnant again while you’re breastfeeding – but it’s most definitely not a reliable birth control method, as many moms have come to learn the hard way!
Of course, there’s also a less pleasant side: Prolactin is indirectly responsible for all the extra fur on your face, belly and other parts of your body. Fortunately, these hair gradually disappears after birth.
Relax and enjoy it
Relaxin is released early on in your pregnancy. It reins in womb movements and also softens the cervix in preparation for birth. It works with progesterone to relax your muscles, ligaments and joints, especially in your pelvis.
In this way, it prepares the way along which your baby will travel when he’s born. But softening muscles can sometimes be quite painful and cause backache and other ailments.
The caring hormone
Oxytocin is sometimes called the magic hormone because it’s responsible for the nurturing behaviour of new moms and dads.
On a more practical level, it’s also responsible for the regular contractions of the uterus while you’re pregnant – like Braxton-Hicks – and it’s the hormone that eventually kick-starts the contractions for labour.
Contractions, while you’re breastfeeding, are also attributed to oxytocin and will help your uterus shrink back to its original size. But wait, there’s more… Human placental lactogen (hPL) is also produced by the placenta and helps ensure healthy foetal development.
It helps your boobs prepare for breastfeeding and make colostrum – that important first milk. There’s a link between too little hPL and small babies because this hormone helps organise your metabolism in such a way that you channel more sugar to the baby.
The thyroid hormone
Thyroxin helps you absorb more oxygen and works with growth hormones to stimulate baby’s growth. It’s also crucial for the healthy development of the baby’s central nervous system.
Thyroid-stimulating hormone ensures the release of thyroid hormones, which regulate your metabolism.
Insulin controls the metabolism of food by you and baby. As your pregnancy progresses, the insulin becomes less effective because it can’t keep up with the glycaemic load. For about two to four per cent of women, this causes diabetes.
Cortisol helps with the development of the baby’s tiny lungs and gradually increases in the third trimester of pregnancy.
On the other hand, studies have shown that too much cortisol, which is the body’s stress hormone, can interfere with the working of progesterone. It also plays an important part in learning and memory.
Share your stories and questions with us via email at email@example.com. Anonymous contributions are welcome.
Don't miss a story!
For a weekly wrap of our latest parenting news and advice sign up to our free Friday Parent24 newsletter.