The placenta is an organ attached to the lining of your womb during pregnancy.

It keeps your unborn baby’s blood supply separate from your own blood supply, as well as providing a link between the two. The link allows the placenta to carry out functions that your unborn baby can’t perform for itself.

The placenta is connected to your baby by the umbilical cord. Your baby is inside a bag of fluid called the amniotic sac.

What does the placenta do?

Oxygen and nutrients pass from your blood supply into the placenta. From there, the umbilical cord carries the oxygen and nutrients to your unborn baby. Waste products from the baby, such as carbon dioxide, pass back along the umbilical cord to the placenta and then into your bloodstream, for your body to dispose of them.

The placenta produces hormones such as progesterone that help your baby grow and develop. The placenta also gives some protection against infection for your baby while it’s in the womb, protecting it against most bacteria. However, it doesn’t protect your baby against viruses.

Alcohol, nicotine and other drugs can also cross the placenta and can cause damage to your unborn baby.

Towards the end of your pregnancy, the placenta passes antibodies from you to your baby, giving them immunity for about 3 months after birth. However, it only passes on antibodies that you already have.

Although not fully developed, the placenta is well established and functional by five weeks after implantation (when you are about 7 weeks pregnant). By this time, the heart of the developing embryo is pumping blood into the placental villi as well as to the embryonic tissues. Development of the maternal blood supply to the placenta is complete by the end of the first trimester of pregnancy .

However, it is too early to assess the placental site by ultrasound at this early stage.

Usually any potential placental complications are picked up at the 20-week NHS scan and many placenta problems generally correct themselves during the pregnancy.

Posterior placenta

The term posterior placenta means that it is lying on the back wall of the uterus, behind the baby.

Anterior Placenta

The term anterior placenta means that the egg has implanted on the side of the uterus which is closest to the front of the abdomen with the baby behind. This does not cause any risk to you or your baby, however it may be more difficult to feel the baby moving early on in your pregnancy.  It could also be more difficult for a midwife to find your baby’s heartbeat. It will move up as the pregnancy progresses, and you will feel more movements as the baby gets bigger and stronger.

Low lying placenta

If the  placenta is also low- lying, it means that the placenta could be partially blocking the cervix (and the birth canal) or fully if the placenta is covering the cervix.

Low-lying placenta is also known as placenta praevia. This means that the placenta is attached to the lower part of the womb near to or covering the cervix and depending on how much the placenta is covering your cervix it may leave you with no option other than to have a Caesarean section.

Unfortunately, with placenta praevia there is a chance of bleeding heavily during the third trimester of pregnancy. The bleeding can be very dangerous. If you do experience bleeding later in pregnancy, whether it is heavy or light, you may be admitted to hospital to ensure you and the baby are safe. The bleeding is painless and tends to be bright red in colour.

It is a long wait from your 20 week ultrasound when you are initially told about your low-lying placenta. You will be asked to come back for a further scan to assess the placental site later on in the pregnancy, usually at 34 weeks, and it is likely that the scan will be done transvaginally (internally) as well as across your tummy.

If the placenta is found to be covering or reaching the cervix, you then will be referred to a Consultant Obstetrician if you are not already under their antenatal care, and will have to be scanned again transvaginally at 36 weeks pregnant. The consultant will then decide on the best and safest way to deliver the baby.

Victoria Davis

Somerset Early Scans

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