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Home   Questions   The Amazing Placenta


About Your Placenta:

The placenta is truly an amazing organ. The word placenta is Latin for cake as this structure is round and flat and is attached to the inside of the womb. This organ is a single structure, one side facing the baby, the fetal portion of the placenta and the other side facing the mother, attached to the womb forming the maternal portion of the placenta.


By a process known as diffusion, nutrients and oxygen are moved from the mother to the baby through the placenta. Waste products and carbon dioxide (deoxygenated blood) are taken from baby and returned back to the mother to be eliminated. Although the mother and the baby’s blood come very close together during this exchange, the blood never actually mixes.

Cell Division & Endometrium Development:

About a day after conception, the fertilized egg divides for the first time. This cell division continues on its way down the fallopian tube. After four or five days this newly fertilized egg, now known as a blastocyst has multiplied and divided into two sets of different cells. The outer set of cells develops into the baby’s part of the placenta and the inner set develops into the embryo, which will become your baby.

At the same time the mother’s endometrium or lining of the womb is undergoing it’s own changes and will become the mothers side of the placenta.

The endometrium increases in thickness and creates a flow path to increase maternal blood flow to where the placenta is attached to the lining of the womb. Spaces within this newly formed placenta are called intervillous spaces and provide channels where the transfer of oxygen and nutrients occur between mother and baby.

The Umbilical Cord

On the baby’s side of the placenta is where the umbilical cord enters this cake like structure called the placenta the other end of the cord enters into the baby’s mid abdomen, the place where we all find our belly button. This umbilical cord contains 3 vessels. One vein and two arteries. Oxygenated blood from the mother passes through the placenta and is carried to the fetus via the single vein, you can see this demonstrated in blue on the colour doppler ultrasound.

The baby’s deoxygenated blood passes via two umbilical arteries back to the placenta which is shown in red. You may notice during your ultrasound scan that the sonongrapher will make sure that the umbilical cord has 3 vessels. At the junction of umbilical cord and placenta, the umbilical arteries branch radially to form chorionic arteries. Chorionic arteries, in turn, branch again and these vessels eventually branch to form an extensive arteriocapillary venous system, bringing the fetal blood extremely close to the maternal blood; close enough for an exchange of nutrients by diffusion but no intermingling of fetal and maternal blood occurs. The exchange of nutrients happens through a series of pressure changes caused by arterial blood pressure and uterine contractions.

The placenta continues to grow throughout pregnancy. A well defined placenta can be seen on an ultrasound by 10 to 12 weeks. A normal placenta can grow to about 15 to 20cm in diameter.

The Placenta Organ:

Because the placenta is primarily a fetal organ, its size is often a reflection of the health and size of the baby. Throughout the pregnancy the placenta will grow continuously and it’s thickness is usually equal to the number of weeks of gestation, about 1mm for each week of the pregnancy. So for example if your baby is 15 weeks in gestation the placenta will be about 15mm in thickness.

Placenta Summary:

So in summary the placenta protects the baby, brings into close relationship two blood circulations that of the Mother and that of the baby to support fetal nutrition. Also near the time of delivery produces hormones that help mature baby’s organs in preparation for life outside the womb.


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