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Medicines taken by a pregnant woman pass through the placenta to the fetus. There are different principles for transporting drugs across the placenta.
This can be passive diffusion, following a concentration gradient from a high concentration environment, i.e. the mother’s bloodstream, to a low concentration environment, i.e. the fetus. Most drugs are transported this way. Active diffusion, or in other words facilitated diffusion, takes place when an additional carrier is necessary for transport. In this way, glucose is transported to the fetus. Active transport – takes place in the opposite direction to the concentration gradient in the environment. This is how amino acids, ions, vitamins are transferred.
Pinocytosis – this material is transported through the cell in a pinocytic vesicle. This is how, for example, immunoglobulins and phospholipids pass. Drugs are only transported across the placenta in a form that is not bound to plasma proteins. The amniotic fluid (one of the membranes) is also involved in the transport of drugs to the fetus. The fetus also ingests the drug when swallowing the amniotic fluid. Until 16-22 weeks of gestation, the fetus absorbs drugs probably also through the skin. The fetus is most sensitive to drugs between days 31 and 71 after the last menstrual period. Before day 31, drugs are all-or-nothing, which means they may kill the embryo or have no effect on it. Later, they may lead to minor or major defects or developmental disorders.
Currently, drugs according to the FDA classification are divided into 5 categories.
Category A – drugs that do not show any risk to the fetus. These are, for example, vitamins.
Category B – studies were conducted on animal fetuses and not confirmed on humans. Generally, these drugs have no negative effects on animal fetuses, and have not been found at all in human fetuses. These include penicillin, digoxin.
Category C – They show teratogenic effect on animals, no studies on humans have been conducted. They can be used in pregnant women when their use will bring benefits greater than the possible side effects. These are, for example, furosemide, quinidine, verapamil.
Category D – The harmful effects of these drugs on the human fetus have been shown, however, in life-threatening situations or serious diseases with ineffectiveness of other drugs, administration of these drugs is justified. These are phenytoin, oral anticoagulants.
Category X – drugs from this group are contraindicated for pregnant women, as well as during the pre-contraceptive period (before pregnancy). These are, for example, thalidomide, anti-cancer drugs.
The basic principle of pregnant women is to adjust any therapy to the fact of pregnancy, and sometimes the therapy should be modified before planning pregnancy. And so, patients with chronic diseases such as diabetes, epilepsy, hypertension should report to the attending physician, i.e. a neurologist, diabetologist and cardiologist, that they plan to become pregnant. Then the attending physician can adjust the dose of drugs, their type, to the woman’s plans. Of course, this would be most optimal, but it is obvious that women get pregnant without necessarily planning it consciously. Then a problem arises, because some drugs, e.g. anti-epileptics, cannot be changed during pregnancy, but only during the planning period. In the case of chronically ill women, the cooperation of a medical team consisting of a specialist in a given field and an obstetrician gynecologist is always necessary.
It cannot be denied that the drugs used in the case of the so-called always raise doubts. colds, inflammations such as bronchitis or urinary tract infections. It should be remembered that any inflammation, especially inflammation associated with increased body temperature, is itself dangerous for the developing pregnancy and may result in miscarriage or preterm labor. Therefore, it requires treatment, and therefore the use of antibiotics. Ampicillin and amoxicillin are considered safe drugs and can be used even in the first trimester of pregnancy. Erythromycin, cephalosporins, clindamycin belong to category B drugs.
However, it is known that streptomycin and kanamycin are harmful, they can damage hearing and bones.
It is impossible to list all medications and their possible side effects here. A rule should be adopted that a pregnant woman must have medical documentation (pregnancy card) with her at all times, so that the doctor ordering the treatment knows about the pregnancy, its duration and possibly any comorbidities.
Text: lek. med. Ewa Zarudzka