The Placenta - All you need to know

The placenta sounds like a planet from another solar system and looks like an alien life form. But it has a very important job to do.

It’s your baby’s life support system while she’s in the uterus, supplying her with the oxygen and nutrients she needs. Your placenta develops rapidly in the first 12 to 13 weeks – it’s thought this may be one reason women usually feel so tired in early pregnancy. It’s fully-formed by week 18 and continues to grow throughout your pregnancy – when it’s delivered it’ll weigh in at around one pound.

What does the placenta do?

First and foremost the placenta provides oxygen to your baby. Each time your heart beats, blood from your arteries flows into the placenta so that oxygen and nutrients flow to your baby. It also carries waste products, such as carbon dioxide, away from your baby. Good functioning of your placenta depends on a good supply of maternal blood – if it’s reduced (which happens if you smoke or suffer from pre-eclampsia, blood flow to the placenta is reduced and this can have an effect on your growing baby.

The placenta keeps any harmful substances away from your baby as well as protecting her against infection – but it can’t always distinguish between what’s good and what’s bad, which is why pregnant women are advised not to drink,smoke or take drugs during pregnancy. Some viruses can pass to your baby from the placenta. Rubella (also known as German measles) can be particularly dangerous if you catch it, and can cause defects such as blindness, deafness and encephalitis (inflammation of the brain) in your baby. If you’re not sure whether you have immunity from Rubella, ask your physician to check.

The placenta also secretes hormones such as chorionic gondotropin, progesterone and estrogen, that all help maintain your pregnancy and also prepare your breasts for breastfeeding. During the last stages of pregnancy, antibodies will pass from you to your baby via the placenta, and these will help to protect her for the first three months. After that her own body will start to build up immunity from what she’s exposed to on a daily basis.

Once your baby is born, the placenta’s job is done. After your baby’s cord is clamped and cut, you’ll deliver the placenta in what’s termed the third stage of labor. You can choose to deliver it naturally or have an injection of Pitocin to stimulate your uterus to contract further to expel it (see the stages of labor). In rare cases the uterus fails to contract to expel the placenta, or a portion of it remains inside. This can result in postpartum hemorrhage and the placenta may have to be surgically removed.

Your placenta is a hero! It protects and nourishes your growing baby. For nine months – so if you get a glimpse of it after the delivery, remember to say a big thank-you for looking after your little one for all those months.

The information in this feature is intended for educational purposes only. If you have any concerns about your health, the health of your child or the health of someone you know, please consult with a doctor or other healthcare professional.

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Last Modified: 10/06/2008

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