Placental Barrier

Placental barrier (from the Greek plakus — flat cake) is a barrier between the blood of the pregnant mother and the fetus in the placenta, with selective permeability in two directions.

It serves as a filter that provides nutrients and respiration for the developing organism, while protecting it from the effects of most microorganisms.

Etiology and pathophysiology

The morphological foundation of the barrier consists of the tissues of the fetal chorionic villi, which interact with maternal blood.

The barrier’s permeability changes throughout pregnancy, significantly increasing by the third trimester.

The barrier possesses unique immunological selectivity. For example, it actively allows maternal antibodies of the IgG class to pass through, providing passive immunity to the newborn. However, larger antibodies of the IgM class do not pass through it.

Clinical significance

The state of the placental barrier determines the risk of intrauterine infection. In medical practice, it comprises key significance in several aspects:

• attention to TORCH infections — the pathogens of these diseases are capable of overcoming the placental defense and causing severe developmental defects;
• assessment of drug safety — when prescribing medications to pregnant women, a key factor is the ability of the molecule to pass through the placental barrier;
• creation of a “medicinal shield” — the therapy of certain infections in pregnant women is aimed at maintaining the drug concentration that prevents the migration of microbes to the fetus.