|What Is The Placenta?
As a baby grows inside the womb its life support system is composed of the umbilical cord, amniotic sac (filled with amniotic fluid) and the placenta. The placenta is a pancake shaped organ that is attached to the uterus and is connected to the baby via the umbilical cord. It grows with the baby and by the time of delivery weighs on average 500g or just over 1 pound and is about 20cm wide and 3 cm thick. Appearance-wise, it looks rough and spongy. The role of the placenta is to provide a link between the blood supplies of the mother and the fetus. It transfers nutrients, oxygen and protective antibodies from the mother's circulation into the baby's circulation and removes waste products from the fetus, back into the mother's blood for excretion by her lungs and kidneys. The placenta also produces pregnancy hormones such as estrogen, progesterone and human chorionic gonadotropin (HCG). These hormones enter the mother's blood supply to make changes in her body to accommodate pregnancy and they prepare her breasts for breastfeeding. Raised levels of HCG is one of the early signs of pregnancy, which is why detection of them in the urine forms the basis of most pregnancy tests. Once the baby is born, the placenta is expelled from the womb and this is sometimes referred to as the afterbirth.
Do Twins Have Their Own Placenta?
Identical twins often share one placenta, but have their own separate amniotic sacs and always have their own umbilical cord. Non-identical twins have separate placentas, amniotic sacs and umbilical cords. See also, twin DNA testing as well as pregnant with twins.
What Can Go Wrong: Abnormalities Of The Placenta
Abnormalities Of Weight
The average weight of the placenta at term is about 500g. The weight varies according to whether the umbilical cord has been clamped early or late, thus imprisoning less or more of the baby's blood. If the baby is born with diabetes or hemolytic disease the placental weight may increase to up to half the weight of the fetus. Doctors usually check the umbilical cord and placenta after birth for signs of abnormalities which could indicate a birth defect or illness in the baby.
Location Of Placenta
The placenta is usually attached to the middle or top of the uterus wall. However, in about 1 in 200 pregnancies the placenta is implanted wholly or partially on the lower segment of the uterus (placenta previa) nearer the cervix. This is a serious abnormality which may cause severe hemorrhage in pregnancy and in particular during childbirth. If you have this problem, your baby may need to be delivered by cesarean section. Anterior implantation of the placenta means it has implanted in the front wall of the uterus. This position makes no difference to the baby and does not affect the outcome of the pregnancy. The only difference is that you might not feel the baby's early kicks or punches because the placenta is cushioned between the baby and your tummy. For this same reason it can be more difficult to hear the fetal heartbeat and it could make an amniocentesis more difficult. In most cases the placenta gradually moves to the posterior position and resolves these challenges.
Placental abruption is the early separation of the placenta from its attachment to the wall of the womb before the baby is delivered (more pictures). If the separation is not severe there is usually little danger to the baby or mother as long as it is treated promptly and precautions are taken. If however the placenta peels away completely the risk to the baby is significantly higher. This is because the baby's life line to food and oxygen from the mother is cut off. It is an uncommon complication which occurs most often in the third trimester of pregnancy but it can happen any time after week 20. Statistically 1 in every 100 pregnant women experiences an abruption, although the severe form may only occur in 1 in every 800 to 1600 deliveries.
Infections Of The Placenta
During normal pregnancy the contents of the womb are protected from infections coming up from the vagina and anus by the cervical mucus plug and by membranes around the amniotic sac. These membranes can prematurely rupture leading to exposure of infection. The most common infection is chorioamnionitis which is characterized by fetal tachycardia (irregular heartbeat) and maternal fever. The risk of infection increases with time (by being over-due) and repeated vaginal examination. As there is a risk of the baby developing pneumonia or the mother developing puerperal sepsis, early induction is usually recommended. Signs of chorioamnionitis include:
• High temperature and fever in the mother.
• Rapid heartbeat in both mother and fetus.
• The womb is tender to touch.
• Vaginal discharge that has an unusual smell.
Placental Insufficiency: When the fetus does not receive enough oxgyen.