Here’s what happens to your body during pregnancy and birth…
Your body during pregnancy – 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.
This hormone is needed to:
- stimulate the placenta – to ensure that 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,
which is needed to enable your body to expand for your growing baby and to provide the space for your baby to be born.
This is a very powerful hormone – its levels are very high during pregnancy.
In early pregnant 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
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 somatomammotropin, is made by the
placenta. It provides nutrition for your baby and it stimulates the milk glands in your breasts in preparation for breastfeeding.
Your body during pregnancy
- 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 cell mass increases 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 & 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 mucous 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.
Temperature increases by about 0.5C – due to increased progesterone and
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 and, with a high level of
oestrogen, creates prostaglandins which helps to soften and open the cervix
- relaxin levels increase in labour to help soften and improve the 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
- high levels of adrenaline are produced when birth is close, to give you a surge of energy as well as the powerful contractions you need
to give birth to your baby
- prolactin is produced throughout pregnancy but levels peak when your baby is close to being born and then stays high to produce milk
while you breastfeed
Hormones after labour
- oxytocin will continue to be produced after your baby is born, to create contractionsto aid the deliver of your placenta. Along with prolactin, it helps to boosts 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 you about 20 minutes after giving birth. It also exists in breast milk, to create a mutual bond between you and your baby.
- 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 every worried or concerned about anything, seek some medical reassurance from your midwife or your GP.
Your body during pregnancy – information taken from:
Anatomy & Physiology for Midwives
Myles Textbook for Midwives
Dynamic Positions For Birth
Janine Smith | a specialist in pregnancy, birth and parent support