When there is a necessity for pregnant women to take drugs during pregnancy, it requires a careful approach in each individual case. Some drugs can negatively affect the pregnancy, the development of the fetus, because of various side effects, which may occur. They can cause risks for the formation of congenital risks and complications for the fetus and the born child. It is suggested that about 1% of all congenital defects are caused by drugs, taken by a pregnant woman.
That’s why, the choice of a necessary drug and it’s dosage for a pregnant woman, regardless of the fact whether it is a prescription drug or not, can be made only by a doctor.
There is a classification of categories of risks for the fetus caused by taking drugs. They are embryotoxicity, teratogenicity and fetotoxicity. These terms determine the time, when a separate drug may cause side effects and birth defects.
Embryotoxicity means the toxic influence of the drug in the first 2 to 3 weeks of pregnancy, from the moment of the fetus development. This refers to the drugs, which are weak acids (phenobarbital, sulfanilamide preparations, acetylsalicylate). A number of hormones, urinary (FUROSEMID, HYPOTHYAZID, DIACARB) and some antitumor drugs possess embryotoxicity.
Teratotoxicity occurs in the case of some effect of some drugs on the fetus from the 3rd to the 8th-10th week of pregnancy. It includes TALIDOMID, sexual hormones drugs, some antiepileptic drugs (PHENITOLIN, VALPROIC ACID), etc.
Fetotoxicity occurs as a result of the influence on a mature fetus. Taking drugs in this period is usually connected with the future mother’s diseases, the pathology of the fetus and the necessity of interrupting pregnancy.
At present, the following critical periods in the life of the fetus are selected, in which the fetus is most sensitive to the damaging effects of drugs:
- From the moment of conception to the 11th day after it, when under the influence of negative factors, including taking drugs, the embryo either dies, or remains alive. Such a phenomenon is due to the fact that at this stage the cells of the embryo are not yet differentiated;
- From the 11th day to the 3rd week, when the fetus starts forming the organs. The type of defect depends on the period of pregnancy. After the end of the formation of an organ system, there are no disorders in their development. Thus, the formation of defects of the neural tube (for example, the absence of the brain - anencephaly) under the influence of teratogens occurs before the 22-28th day after insemination (until the closing of the neural tube);
- Between the 4th and the 9th week, when the danger of delayed fetal growth is continued, but the teratogenic effect is practically no longer observed;
- Fetal period: from the 9th week up to the birth of the child. In this period of growth, structural defects usually do not occur, but there may be a disruption of post-natal functions and various behavioral defects.
How Do Drugs Affect The Fetus?
The ability of drugs, taken by the mother, to pass through the placenta highly depends on their physicochemical properties. Through the cellular membranes, the most readily available are fat-soluble drugs and much worse - water-soluble drugs. Doctors began to take into account that the lack of some vitamins, microelements (including iron) can slow down the fetal development and cause the further suppression of the physical and mental development of the child, which may cause the development of autism in future. At the same time, their excessive taking may also lead to irreparable troubles - to be the cause of congenital deformities.
Small molecules penetrate the placenta very well and the drugs with a molecular weight of more than 1000 units do it much worse. The only anticoagulant drug HEPARIN has a larger molecule and does not pass through the placenta, while the anticoagulants of indirect action (NEODIKUMARIN, PELENTAN, VARFARIN), which are effective only through the administration to the organism and do not affect the clotting when mixed with blood outside the organism, can penetrate the fetus and reduce blood-clotting.
If the medicine penetrates well through the placenta, it can be accumulated in the fetal tissues and negatively affect the fetus. It causes severe complications in the child in future. The continuous use of an antibiotic STREPTOMICIN, which has a wide spectrum of antimicrobial activity during a 3-5-month pregnancy, may cause deafness in the child. Antibiotics from the group of tetracycline (METATSIKLIN, TETRACYCLIN, RONDOMICIN, etc.) negatively affect the process of bone formation; anticonvulsants (DIFENIN, HEXAMIDINE) may have negative effects on the child's central nervous system’s functions; sulfonamide drugs (ETAZOL, SULFADIMESIN, SULFALEN, BISEPTOL, etc.) may have a toxic effect on erythrocytes - red fetal blood cells; many sleeping pills (PHENOBARBITAL) suppress the respiratory center.
At the same time, it should be admitted, that pregnant women often suffer from chronic diseases of internal organs. Some of them experience the exacerbations and complications of chronic diseases, new diseases appear and it can be dangerous for the health and even for the life of a woman and a fetus. The abolition of drugs in these cases is harmful. That's why the doctor tries to prescribe the drugs that are the safest for the fetus and at the same time effective for the treatment of the diseases, which pregnant women have.
There are the following categories of risks, which are developed by the American Administration for Control of Medicines and Food Products and are taken into consideration through the world, prescribing the drugs to pregnant women:
- A – the drugs that were taken by a large number of pregnant women and women of childbearing age without any facts of their influence on the possibility of congenital anomalies or risks for the fetus. (PARACETAMOL, CLOTRIMAZOL - locally, PENICILLINS, antacid drugs - ALMAGEL, MAALOX, etc.);
- B – the drugs, which were taken by a limited number of pregnant women and women of childbearing age, without any facts of their influence on the possibility of birth defects or damage to the fetus. At the same time, studies with animals didn’t show any increase in the frequency of fetal defects (HEPARIN, DICLOPHENAC, IBUPROFEN, AZITHROMYCIN, ACYCLOVIR, METROPIDAZOL, etc.);
- C – the drugs that have demonstrated teratogenic or embryotoxic effects as a result of animal studies. There are suspicions about a damaging effect on the fetus or newborns (due to the pharmacological properties of the drugs), which does not cause the development of congenital defects. The experiments on people were not conducted (ASPIRIN, DEXAMETHASON, DUFASTON, diuretics, etc.);
- D – the drugs that cause or it is suspected that they may cause congenital anomalies or irreversible damage to the organism. It is necessary to correlate the risk to the fetus with the potential benefit for the mother using the drug. (Sedative-like barbiturates, DOXYCYCLINE, TETRACYCLINE, etc.)
- X – the drugs with a high risk of the development of congenital defects or persistent fetal destructions, as there are facts of their theatogenic or embryotoxic effects on both animals and humans. They should not be taken during pregnancy.
Thus, the prescription of drugs to a future mother in the first trimester, second trimester and the third trimester of pregnancy always was and remains an important problem because of the risk of occurred side effects. The doctor takes into consideration the method of application, the used dosage of the drug, calculates whether the benefit overweighs the risk. That is why, when choosing and taking drugs, the self-initiative of a pregnant woman and her relatives is not acceptable.