Classification of malformations
Anomalies are systematized according to the specific way the organ has changed:
- Changes in size: excessive growth (hypergenesis), underdevelopment (hypoplasia or hypogenesis), and complete absence of an organ (aplasia or agenesis).
- Changes in shape: for example, horseshoe kidney, clubfoot, or bicornuate uterus.
- Anomalies of position: heterotopia or ectopia (aberrant thyroid gland, cryptorchidism).
- Increase in number: polydactyly, presence of accessory ribs, hermaphroditism.
- Atavisms: fistulas, as well as lateral and median neck cysts.
- Duplication anomalies: conjoined twins.
Internal teratogenic factors
Internal causes include gametopathies—genetic defects representing hereditary pathology. They arise due to mutations.
- Monogenic anomalies are associated with a defect in a single gene (e.g., syndactyly or polydactyly).
- Polygenic and chromosomal mutations lead to the formation of multiple malformations simultaneously.
A significant risk factor for the appearance of such mutations is mixed consanguineous marriage.
External teratogenic factors
This group includes infectious, chemical, and physical effects on the pregnant woman's body (although in about a third of cases the exact cause cannot be determined).
External factors can harm the fetus directly or indirectly—through damage to the amnion and placenta. For example, trauma or inflammation can provoke the formation of amniotic bands (adhesions) that compress the fetal limbs, causing their deformation or even intrauterine amputation.
- Infections: pathogens penetrate the fetus through the placenta. Viruses pose the greatest danger (measles, chickenpox, viral hepatitis, poliomyelitis, herpes). Bacteria (syphilis, diphtheria, scarlet fever) and other agents (cytomegalovirus, toxoplasmosis, listeriosis) also have an effect.
- Chemical factors: agricultural poisons (insecticides, pesticides), medications (antibiotics, psychotropics, sedatives, amidopyrine), as well as nicotine and alcohol.
- Physical factors: ionizing radiation, vibration, mechanical trauma, hypothermia, or hyperthermia.
Critical periods and prevention
The fetus is most vulnerable to teratogenic effects at specific stages of pregnancy:
- Days 3–5: the period when the zygote implants.
- Weeks 3–6: the period of organogenesis, which is considered the most sensitive to harmful factors.
Prevention of congenital anomalies is based on two pillars: identifying genetic risks in prospective parents at the planning stage and maximally eliminating any external teratogenic influences during pregnancy.
Briefly: answers to topical questions
Which viruses are capable of crossing the placenta and causing congenital malformations?
Viruses capable of crossing the placenta and causing congenital malformations include rubella, measles, smallpox, hepatitis, herpes, poliomyelitis, and cytomegalovirus.
- Rubella (Rubella) ranks first among viruses affecting the fetus and has a pronounced teratogenic effect.
- Cytomegalovirus infection (Cytomegalia) is part of the TORCH infection group.
- Herpes virus infection (Herpes) also belongs to the TORCH complex.
- Other viruses include chickenpox, measles, viral hepatitis, and poliomyelitis.
Which groups of medicinal products have a proven teratogenic effect?
Chemical teratogenic factors cited in sources include:
- Sedatives.
- Psychotropic drugs.
- Certain antibiotics.
- Amidopyrine.
- Thalidomide has a powerful teratogenic effect and can cause phocomelia (limb underdevelopment, "seal limb").
How are congenital malformations classified according to the timing of the damaging factor's action?
According to the timing of the damaging factor's action on the fetus, congenital malformations are classified into four main groups:
- Gametopathies—defects originating in germ cells during gametogenesis.
- Blastopathies—disorders arising during the cleavage of the blastocyst (the first 15 days after fertilization).
- Embryopathies—disorders developing upon exposure to the embryo from the 15th–16th day to the 8th–10th week of pregnancy.
- Fetopathies (fetus)—disorders arising from exposure to the fetus starting from the 10th week (from the 76th day) until birth.
Which specific syndromes are characteristic of chromosomal mutations causing multiple malformations?
Chromosomal mutations causing multiple malformations are characterized by the following specific syndromes:
- Down syndrome—occurs due to trisomy 21.
- Patau syndrome—develops as a result of trisomy 13.
- Edwards syndrome—caused by trisomy 18.
- Turner syndrome—occurs with sex chromosome monosomy (karyotype 45, X0).
To remember the types of organ size changes, use the prefixes: hyper- (many, hypergenesis), hypo- (few, hypoplasia), a- (negation, absence of an organ, aplasia).
Class and exam questions
During which period of pregnancy is the fetus most vulnerable to the formation of malformations?
The most critical period is organogenesis (weeks 3 to 6), as well as the moment of zygote implantation (days 3–5).
What are gametopathies?
These are genetic defects associated with gene or chromosome mutations that underlie hereditary (internal) causes of malformations.
How do amniotic bands affect the fetus?
They arise due to inflammation or trauma of the amnion and can compress the fetal limbs, leading to their severe deformation or even amputation.
What else to study on this topic
- Mechanisms of amniotic band formation
- Features of viral infections as teratogenic factors
- Examples of monogenic and polygenic anomalies
- Atavisms and vestigial structures in surgical practice
- Diagnosis of developmental anomalies in newborns
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