After the fertilised egg has travelled along the fallopian tube, it embeds into your uterus and this is where the placenta develops and attaches to the lining of your womb. The placenta is linked to your baby by the umbilical cord.
The main purpose of the placenta is to keep your blood supply separate from your baby’s blood supply as you both may have different blood types. As your baby grows inside your womb, your body will pass oxygen and food through the placenta and the umbilical cord and onto your baby. Your baby’s waste products and carbon dioxide will then go back via the umbilical cord where the placenta will put them back into your bloodstream so that your body can dispose of them.
The placenta also protects your baby against infection and most types of bacteria, although it cannot protect your baby against a virus such as German Measles (rubella). The placenta also cannot stop alcohol, nicotine or drugs passing through it. The placenta helps your baby to grow by producing hormones to aid development. In the final weeks of pregnancy, the placenta will pass antibodies that you have in your body to your baby to help them fight infection after birth: this lasts for approximately three months.
After your baby is born and the umbilical cord has been cut, there is no need for the placenta. You will need to deliver the placenta through your vagina. This is known as the third stage of labour and now the placenta is referred to as the afterbirth. Most women do not have any problems with their placenta although after you have delivered your placenta it will be inspected by your midwife to ensure it has come out cleanly. Some women decide that they would like to keep their placenta although most allow the midwife to dispose of it as necessary. If you need more information about this or any stage of your pregnancy, speak to your midwife or doctor.
There are three main problems that may affect your placenta though these are normally quite rare. They are:
- Placenta praevia (low-lying placenta)
- Retained placenta
- Placental abruption
If the fertilised egg attaches to the lower part of your uterus, the placenta will develop in a low-lying position and near or covering your cervix (the baby’s exit). For most women, the placenta will be pulled up away from the cervix as your uterus expands. During your 18-22 week scan, the position of your placenta will be recorded and if it is still low, it is diagnosed as placenta praevia. However, there is still time for the placenta to be naturally pulled up away from the cervix and you will be offered another scan at approximately 32 weeks to check the position again. If the placenta does not move fully away from the cervix, your baby will need to be delivered by caesarean.
This image shows that the placenta is fully covering the cervix. This is classified as Type IV. A partially covered cervix is referred to as Type III, when the placenta just touches the cervix is Type II and a Type I placenta praevia is where the placenta is low but not touching the cervix. Whereas Type II, III and IV will all require a caesarean, Type I may be able to be delivered naturally through the vagina.
If you have placenta praevia, there is nothing you can do apart from waiting to see if it will move by itself. It can be a worrying time for you but you must try and relax as you will be cared for by experienced midwives, doctors and consultants should your placenta not move. It is important that you continue to eat healthily throughout your pregnancy and try and eat plenty of foods that contain iron to reduce the risk of you becoming anaemic.
If your placenta continues to stay low, there is a chance that you may bleed bright red blood towards the end of your pregnancy: this is likely to be painless and come on suddenly. If this should happen, it is important that your contact your midwife or doctor immediately as you will need medical treatment as quickly as possible.
The third stage of labour involves you pushing the placenta and membranes out through your vagina; after this has happened your midwife will examine the placenta to ensure it is complete and that there is none left inside your uterus. If parts of the placenta or the membranes remain in your uterus this is known as retained placenta. You will also be diagnosed with retained placenta if it takes a long time to deliver the placenta.
A retained placenta is very rare with less than 10 in 1,000 hospital births in England being diagnosed with this problem.
There are three main reasons why you may get a retained placenta:
- Placenta accreta: this is where part of the placenta embeds so deeply into the wall of the uterus that it remains attached.
- Trapped placenta: this is where the placenta has come away from the uterus cleanly but then gets trapped behind the cervix.
- Uterine atony: this is when the uterus stops contracting and therefore the placenta cannot separate from the wall of the uterus.
If you have a retained placenta, your uterus will be unable to contract properly and will not be able to contract down and shut off the blood vessels inside the uterus, this means that you will continue to bleed and you will be at risk of the bleeding increasing. Continuous heavy bleeding during the first 24 hours after labour is known as Primary Postpartum Haemorrhage (PPH). Secondary PPH can sometimes occur if small parts of the placenta remain inside the uterus and if they cause heavy bleeding afterwards.
If you are having trouble delivering the placenta during the third stage of labour, your midwife should encourage you to breastfeed your baby as this helps encourage the uterus to contract naturally and help to push the placenta out. If you are not planning on breastfeeding your baby, nipple stimulations might work in the same way. Your midwife will also encourage you to change position as a squatting or upright position may help the placenta to come away more easily.
An injection of oxytocin will also help your uterus contract and your midwife may try to gently pull the placenta out using the cord. If this fails you will need to have the placenta removed manually and you will need either a spinal, epidural or general anaesthetic, antibiotics to reduce the risk of an infection and possibly a catheter inserted to empty your bladder.
Unfortunately if you have a retained placenta with a birth, you are at more risk of having a retained placenta on subsequent births. Ensure your midwife is aware of your pregnancy history and discuss your options with her or your doctor. A retained placenta is also more common in premature births as the placenta is designed to last for 40 weeks and may not be ready to come away earlier even if the baby has been born.
This very serious complication of the placenta is when the placenta comes away either partially or fully from the lining of the uterus before your baby is born. Blood will then accumulate behind the placenta causing it to move further away from the lining and your uterus. If this happens, your baby may get deprived of oxygen and also the nutrients that it needs for development. Placental abruption can also cause severe bleeding to both you and your baby. Sadly, if the abruption is small and goes unnoticed it may cause your baby to have growth problems, be born prematurely, or to die whilst still in the womb. It is a very sad fact that placental abruption is one of the most common causes of stillbirth and neonatal death in the UK.
Unfortunately, we do not know exactly what causes a pregnant woman to have a placental abruption, but it is more likely to happen for women who:
- Have suffered a placental abruption in a previous pregnancy
- Have had trauma in the abdominal area
- Have high blood pressure or hypertension
- Use cocaine
- Have too much amniotic fluid known as polyhydramnios
- Have pre-eclampsia
- Have their waters break prematurely
- Have had lots of babies
- Are older (the risk increases with age)
- Have previously had a caesarean
Placental abruption is most common during the third trimester but can happen from 20 weeks onwards, it affects approximately 1 in 200 pregnancies.
Some of the signs that may indicate placental abruption include:
- Vaginal bleeding: this may be a sudden gush of blood or it may be small spotting amounts. The blood will be dark.
- Tender uterus
- Abdominal pain
- Back pain
- A contraction that is continuous
- If your waters break and it is bloody (Your waters should be clear)
- Excessive thirst
- Your baby is not moving as frequently
If you experience any of these signs, it is important that you phone your midwife immediately. If you losing a lot of blood or feel weak, faint, pale, sweaty, disorientated or your heart is pounding, you must call 999 immediately.
On arrival at the hospital, you will be examined and checked to rule out any other reasons for the bleeding. If you are diagnosed with placental abruption and you are near you due date, your baby will be born straightaway, normally by caesarean. If you are not near the end of your pregnancy, the medical staff may try to delay delivery although they will closely monitor both you and your baby throughout and you will need to stay in hospital so that your baby can be delivered should the abruption get worse.
My Jenny, mum to William and James