What does the placenta do?

When you become pregnant, your body doesn’t just grow a human being, it develops a whole new organ to nourish your baby too.

The placenta, sometimes referred to as the afterbirth, has a vital job to do. It supports your baby, giving them the things they need, including oxygen and food and taking away the things they don’t as waste.

What is the placenta?

The placenta is an organ which is attached to the lining of your womb and linked to your baby through the umbilical cord. When you first become pregnant, the fertilised egg will be supported by yolk sac, which is able to nourish the embryo and help it develop.

By four weeks of pregnancy, the placenta starts to grow, starting as just two layers of cells. One of these layers will tunnel into your womb lining, establishing a supply of oxygen from you to your baby, while the other will start producing the pregnancy hormone hCG.

The placenta takes over from the yolk sac and becomes your baby’s support system from around 10 weeks. It is a similar shape to a pancake and will eventually grow to around 20cm in diameter, be around 2.5cm thick at its centre and weigh about 500g (just over 1lb).

How does the placenta work?

The umbilical cord links your baby to the placenta and contains one vein and two arteries. These branch out into a network of blood vessels in the placenta, which then divide into chorionic villi – tiny fingers of tissue, which allow your blood to supply nutrients and take away waste products. The villi also work like a filter, preventing some viruses and bacteria from reaching your baby.

The placenta plays a number of essential roles in your baby develop. It delivers oxygen and nutrients like vitamins, glucose and water from your body and sends them to your baby through the vein in the umbilical cord.

Waste products like carbon dioxide travel from your baby back to the placenta through the arteries in the umbilical cord and the placenta releases them into your circulatory system. In effect, the placenta takes on the role of your baby’s lungs, kidneys and liver until they are born.

The placenta also passes on valuable antibodies from your bloodstream, giving your newborn some protection from illnesses until they are old enough for their first set of vaccinations. And it produces hormones which play a vital role in your baby’s growth and development.

Will my placenta be monitored during pregnancy?

As the placenta has such an important role, the sonographer carrying out your ultrasound scans at around 12 and 20 weeks will check its position and that there are no obvious issues. If you have a blood-clotting disorder, have high blood pressure, have had surgery on your uterus in the past or have experienced issues with your placenta in earlier pregnancies you are more at risk of developing problems and will be monitored more closely.  

What happens to the placenta when my baby is born?

After your baby is born, you will need to give birth to the placenta separately. This is known as the third stage of labour and you will start having contractions again.

Don’t worry though, the process isn’t anywhere near as intense as giving birth to your baby. You can choose to have a natural (physiological) third stage where you allow time and nature to take its course or you can opt for active management.

This is where you will be given an injection of oxytocin in your thigh to make your uterus contract ready to deliver the placenta. Once the placenta has come away from the lining of the womb, your midwife will gently pull the umbilical cord to ease it out.

An actively managed third stage will typically take around 30 minutes, whereas a physiological third stage will usually take longer and is not recommended in all cases. If you have bled heavily or your placenta does not come away, you may be advised to have an oxytocin injection to get things moving.

If your baby is delivered by caesarean section, the placenta will be removed from your uterus as part of the procedure.

When your placenta is delivered, it will be checked carefully by your midwife to make sure it is complete. This is because sometimes the placenta breaks up and part of it may remain in your womb which can make you very ill.

Any fragments must be removed to prevent any infection or bleeding. In most cases, the placenta is disposed of after it has been checked, however you can ask for yours if you wish.

Some cultures like to keep the placenta and bury it, while some women choose to eat it or turn it into capsules as they believe the nutrients will benefit them. If you do want to do something with your afterbirth, talk to your midwife about it during your pregnancy so it can be included in your birth plan.