How pregnancy affects the body – how it changes and grows and what the different hormones do.
How pregnancy affects the body – hormones
As soon as the placenta starts to form and the cells, which are fast becoming your baby, have implanted into the side of the uterus, your baby will produce human chorionic gonadotrophin (hCG) – these levels will double every couple of days, reaching its peak by about 10 weeks when the levels start to level out as the placenta starts to function.
Oestrogen – This hormone is needed to:
*stimulate the placenta – to ensure it grows and works
*develop your baby’s lungs, liver and kidneys
*work with progesterone to grow your breast tissue for milk production
The rapidly growing levels of oestrogen in early pregnancy may cause sickness and nausea.
Oestrogen and relaxin creates the loosening of the ligaments and joints throughout the body. This is needed to enable your body to expand for your growing baby and to provide the space for your baby to be born.
Progesterone – This is a powerful hormone and its levels are very high during pregnancy.
In early pregnancy it is needed:
*to stimulate blood vessels to increase the blood flow to your womb
*for the glands in the lining of the womb to produce the nutrients that are needed for your embryo baby
*to enable the lining of your womb to thicken and to aid the attachment of the placenta and the implantation of your embryo baby
*to form the placenta
Throughout pregnancy, progesterone is needed:
*for the development of your baby
*to prevent your womb contracting before labour needs to start
*to prevent lactation until after your baby is born
*to help strengthen the muscles of your pelvic wall for labour
Oxytocin – the posterior pituitary gland releases oxytocin during pregnancy. This will increase at the end of pregnancy to stimulate the contractions needed for labour.
Human placental lactogen (hPL) – this hormone, also known as human chorionic somatomammotrophin, is made by the placenta. It provides nutrition for your baby and it stimulates milk glands in your breasts in preparation for breastfeeding.
How pregnancy affects the body
*during the second trimester your heart is working 40% harder than normal – your heart is working efficiently to pump more blood with each beat
*your heart rate may increase by about 15 beats per minute
*blood volume increases throughout pregnancy
*plasma can increase by 40-50% and red blood cells increase by 20-30% which can mean you need more iron and folic acid
*throughout pregnancy, the air going in and out of your lungs increases by about 50%, with higher blood oxygen levels – you could consume
10-20% more oxygen
*the shape of your chest changes in pregnancy as your diaphragm can rise by 4cm, which reduces lung capacity by 5%
Your cervix and uterus
*the cervix acts as a barrier against infection during pregnancy and it protects your baby by staying firmly closed until labour starts. The hormone progesterone causes the cells of the cervix to create mucus, which forms the mucus plug.
*your uterus will contract throughout pregnancy – these Braxton Hicks contractions will help to aid the blood circulation to the placenta.
Nausea and vomiting
*This affects about 70% pregnant women – it is usually caused by relaxed stomach muscles and increased oestrogen
*About 20% of women will experience it throughout pregnancy
About 50% of all pregnant women experience an increased appetite
This affects between 30-70% of women at some point in pregnancy. It is caused by progesterone which relaxes the oesophageal sphincter.
Weight gain in pregnancy
The expected weight gain in pregnancy is: 4kg (9lb) in first 20 weeks
and 8.5kg (1stone 5lb) in last 20 weeks (12.5kg in total)
- Boobs: 0.4kg (1lb)
- Fat: 3.5kg (12lb)
- Placenta: 0.6kg (1lb5oz)
- Baby: 3.4kg (7lb 7oz)
- Amniotic fluid: 0.6kg (1lb 5oz)
- Increased uterus size: 1kg (2lb 3oz)
- Increased blood volume: 1.5kg (3lb 5oz)
- Extra fluid: 1.5kg (3lb 5oz)
Half of all pregnant women will experience deeper colouring on their face. It is more common in dark haired women.
This increases by about 0.5C – due to increased progesterone and
Headaches The anterior pituitary gland can double in size, which can be the
cause of headaches during pregnancy
Your breasts may swell due to increased blood supply and hormones:
- oestrogen = growth of lactiferous tubes and ducts as well as fat
- progesterone= alveoli buds and their ability to secrete milk
- prolaction = production of colostrum
Hormones in labour
For your baby to be born, the muscles of your womb need to contract and your cervix needs to soften and open> A balance of hormones working together makes this happen.
Oxytocin stimulates the uterus to create contractions. With a high level of oestrogen, it creates prostaglandins which helps to soften and open the cervix.
Relaxin levels increase in labour to help soften and improve flexibility of your cervix, uterus and pelvis to aid the birth of your baby.
Beta-endorphins – your natural opiate – is released to help you manage the contractions. It aIso aids the production of prolactin and
prepares your baby’s lungs for birth.
Adrenaline – high levels are produced when birth is close. This gives you a surge of energy as well as powerful contractions to give birth to your baby.
Prolactin – this is produced throughout pregnancy but levels peak when your baby is close to being born. Levels then stay high to produce milk while you breastfeed.
Hormones after labour
Oxytocin is produced after your baby is born, to create contractions to aid the delivery of your placenta. Along with prolactin, it helps to boost your feelings of happiness and love so you will protect and look after your baby.
Beta-endorphins are also crucial for breastfeeding – levels peak in your body about 20 minutes after giving birth.
Prolactin is produced to enable your breasts to make milk for your baby. With oxytocin and beta-endorphins, it also helps to create euphoria in new mums.
And this is just the basics – there’s a lot going on in your body during pregnancy, labour and shortly after birth. If you are ever worried or concerned about anything, seek some medical reassurance from your midwife or your GP.
Just send me a message here with your pregnancy, birth and baby questions.
Janine Smith | A specialist in pregnancy, birth and working with parents