Placentation

Definition - What does Placentation mean?

Placentation is the development, structure, or organization of the normal placenta within the pregnant uterus. The placenta is a highly enriched organ that connects the mother’s uterus to the developing fetus, mediating delivery of nutrients and oxygen to - and removal of wastes from - the fetus. The placenta also produces hormones that help sustain a pregnancy. Placentation begins approximately 5 to 8 days after fertilization and ends when the placenta is delivered with the baby at birth. Infertility treatments can lead to placentation abnormalities that in turn adversely affect the pregnancy outcome.

FertilitySmarts explains Placentation

The placenta starts developing when the fertilized egg (now called a blastocyst) implants itself into the uterine wall. If the blastocyst incorrectly attaches too low in the uterus, it results in a condition called placenta previa. Similarly, if the blastocyst attaches too deep to the uterine wall, placenta accreta will occur.

The blastocyst comprises of an inner component (that becomes the embryo) and the outer layer of trophoblast (which forms a large part of the future placenta). The trophoblast itself encloses two cell layers – the inner cytotrophoblast and the outer syncytiotrophoblasts. Cytotrophoblast cells are the stem cells that play a vital role in the placental growth and are capable of dividing throughout pregnancy.

Following attachment, the blastocyst starts invading the uterus, during which cells from the trophoblast layer travel into the deeper layers. Moreover, these cells also travel into the uterine blood vessels called spiral arteries, transforming them into larger and spacious vessels during placentation. If the trophoblast fails to invade and the spiral artery is unable to transform, conditions like preeclampsia and restriction of fetal growth ensue due to interruption of the normal blood flow between the uterus, placenta, and, the fetus.

IVF may also cause placentation defects including placenta accreta and previa. Various factors may account for this observation. Sometimes IVF may induce local trauma to the uterine wall that results in a defective uterine lining and the placenta being attached too deep in the uterine wall. At other times, a biological factor like an impaired response to trophoblast invasion can contribute to abnormal attachment of the placenta. In addition, the stimulation protocols used during IVF may trigger some functional and structural changes in the uterine lining or disrupt the formation of related genes in the endometrium, causing placentation defects.

Other complications related to abnormal placentation include low birth weight and premature delivery.

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