From Mother to Child: The Placenta's Role

By Hunter, Beatrice Trum | Consumers' Research Magazine, January 2001 | Go to article overview

From Mother to Child: The Placenta's Role


Hunter, Beatrice Trum, Consumers' Research Magazine


The placenta is a special organ found in all pregnant mammals. It forms inside the mother's uterus and connects her with the developing fetus to provide it with nourishment and healthy growth.

First of two parts

The placenta serves several functions. It acts as a complex filtering organ. Oxygen-rich blood goes from the mother's body to the placenta, where it is carried by the umbilical cord to the fetus. The blood circulates through the fetus and supplies it with oxygen. Then, the oxygen-poor blood is carried back by the umbilical cord to the placenta, where it is made oxygen-rich again. In addition, the placenta acts as a conduit to bestow the mother's beneficial endocrine, immune, and metabolic functions to the embryo.

Formerly, the placenta was regarded as an invulnerable barrier, shielding the fetus against harmful substances. This perception was upset in the early 1960s with the dramatic thalidomide case. This mild tranquilizer had been regarded as so safe that it was sold as an over-the-counter product to pregnant women in Europe. Some 5,000 infants, many with gross malformations, were born to women who had taken the drug. It was discovered that thalidomide goes through the placenta.

The placenta allows substances both nourishing and potentially harmful to pass through. After the thalidomide incident, pregnant women have been cautioned to avoid all over-the-counter drugs, and doctors have been hesitant to prescribe any drugs except those that are deemed essential, in special circumstances, for the health of the pregnant women and/or her fetus.

Immunity delivered through the placenta is an example of successful "transplantation." In a sense, for more than nine months, the developing fetus accepts a foreign graft. The placenta protects the mother's immune mechanism from being rejected and destroyed by the fetus. Maternal lymphocytes (blood cells that fight infection) are delivered through the placenta to the fetus. (See "Acquired Immunity", page 24.)

The placenta produces proteins similar in structure and function to some pituitary gland hormones. Also, the placenta synthesizes a protein similar to beta-endorphin, a pituitary protein. This protein exerts psychological and behavioral effects, but not hormonal effects. It is suggested that this pituitary protein's function in the placenta is to help alleviate childbirth pain.

Human placental lactogen (HPL) is a circulating hormone that can be used as a reliable indicator of fetal well-being. Other terms are used to denote HPL, including somatomammotropin (HCS), chorionic growth hormone prolactin (CGP), and purified placental protein (PPP). Measuring this hormone's level provides a useful clue about many disorders of high-risk pregnancies, such as hypertension and diabetes. HPL measurements also can screen pregnancies that appear normal but have placental insufficiencies that would otherwise become apparent only at the time of labor and delivery of the infant. Measuring HPL is helpful, too, to diagnose fetal distress and/or asphyxia; to predict the outcome of vaginal bleeding; and the likelihood of miscarriage in early pregnancy.

Nutrients and Toxins. The mother's diet needs to provide all the necessary nutrients, and to exclude toxins as much as possible. Substances such as caffeine, saccharin, alcohol, and nicotine readily pass through the placenta. The fetus may be far more affected by these toxins than the mother, especially if such substances accumulate.

Even a moderate restriction of nutrients during pregnancy may cause some degree of fetal growth retardation. Maternal malnourishment interferes with cellular growth of the placenta, alters RNA metabolism, and lowers the placenta's ability to transfer nutrients. Even mild malnutrition reduces the mass of peripheral villi (small structures that take up nutrients) and results in a reduced placental transfer of nutrients to the fetus. …

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