Periods of ontogenesis
Ontogenesis is the entire cycle of an organism's development from zygote formation to death. It is divided into three stages:
- Prezygotic period. Includes the formation of sex cells (gametes) with a halved (haploid) set of chromosomes via meiosis.
- Prenatal (antenatal) period. Covers all intrauterine development from the moment of fusion of the egg and sperm (restoration of the diploid set).
- Postnatal period. Begins after the child is born.
The onset of the prenatal period includes the cleavage stage of the zygote, which turns into a blastula. The latter consists of the trophoblast (future placenta) and embryoblast (embryo body). This is followed by gastrulation with the formation of three germ layers (ecto-, ento-, and mesoderm) and subsequent histo- and organogenesis.
Classification of prenatal pathology
Depending on when the pathological factor affected the fetus, four forms of disorders are distinguished:
- Gametopathies. Occur even before conception due to mutations in the parents' germ cells. They often lead to hereditary diseases, malformations, or early pregnancy loss.
- Blastopathies. Occur within the first 15 days after zygote formation. These include implantation disorders (e.g., ectopic pregnancy), twinning defects, and the formation of "empty" gestational sacs. About half of embryos perish during this period.
- Embryopathies. Span from the 16th to the 75th day (the organogenesis phase). It is during this time that most congenital malformations and teratomas are formed.
- Fetopathies. Occur from the 76th day until birth. They manifest as fetal growth restriction, infections, metabolic disorders, hemolytic disease, as well as specific malformations (persistence of embryonic clefts or structures, or malposition of organs).
Main causes of pathologies
A wide variety of factors can influence fetal development:
- Genetic: gene and chromosomal anomalies.
- Maternal: internal organ diseases (diabetes, heart defects, renal pathology), obstetric complications (preeclampsia, placental insufficiency).
- External teratogens: radiation, alcohol, tobacco, industrial poisons, and toxins.
- Infections: the TORCH group and other microorganisms.
- Immune: maternal-fetal blood incompatibility (e.g., Rh factor).
- Deficiencies: lack of vitamins and trace elements in the pregnant woman.
Perinatal terminology
Strict criteria are used for the proper assessment of newborn condition and statistics:
- Live birth. An infant is considered live-born if, after extraction from the mother, they exhibit at least one sign: spontaneous breathing, heartbeat, umbilical cord vessel pulsation, or muscle movement.
- Stillbirth. Death of a fetus before its complete birth. It can be antenatal (before the onset of labor) or intranational (during labor).
- Prematurity. This is the birth of an infant at a gestational age of less than 37 completed weeks. It is often accompanied by a birth weight of less than 2,500 g and a length of less than 45 cm; however, low birth weight per se is not an absolute criterion for prematurity (it also occurs in full-term infants).
- Perinatal mortality. Reflects the number of stillbirths and infants who died within the first 6 days of life per 1,000 total births.
Briefly: answers to topical questions
Which specific infectious pathogens are included in the TORCH group?
The TORCH group includes:
- T (Toxoplasma) — toxoplasmosis.
- O (Other) — other infections, including syphilis, chlamydia, enterovirus infections, hepatitis A and B, gonorrhea, and listeriosis.
- R (Rubella) — rubella.
- C (Cytomegalovirus/Cytomegalia) — cytomegalovirus infection.
- H (Herpes) — herpesvirus infection.
What are the morphological signs of fetal prematurity upon autopsy?
Morphological signs of prematurity include:
- Skin — lanugo hair (lanugo) on the face, shoulders, and back.
- Nails — underdevelopment of the nail plates.
- Auricles — soft due to poor cartilage development.
- Skull — soft bones; premature infants may have open sutures and small and lateral fontanelles.
- Bone system — absence or underdevelopment of ossification centers in the epiphyses of long tubular bones.
- Genitalia — in boys, testes are not descended into the scrotum; in girls, the labia majora do not cover the labia minora.
Which medications have a proven teratogenic effect?
Sources indicate teratogenic or embryotoxic effects for the following drugs:
- Anticonvulsants — valproic acid, carbamazepine, hydantoin, trimethadione.
- Antineoplastic drugs — methotrexate, aminopterin, mercaptopurine, cyclophosphamide, actinomycin, sarcolysin.
- Antibacterial drugs — streptomycin and tetracycline.
- Psychotropic agents — imipramine, meprobamate; diazepam is contraindicated in the 1st trimester.
- Hormonal drugs — diethylstilbestrol, antithyroid drugs, androgens, and high doses of progestogens.
- Other drugs — thalidomide, warfarin, isotretinoin.
What external teratogens can cause fetal malformations?
External teratogenic factors capable of causing fetal malformations include:
- Physical factors — ionizing radiation.
- Chemical factors — alcohol, nicotine, narcotic substances, medications, as well as industrial and household toxins, including lead, methylmercury, phosphorus, benzene and its derivatives, phenol, formaldehyde, polychlorinated biphenyls, and pesticides.
- Biological factors — infectious agents, including rubella virus, cytomegalovirus, herpesviruses, and varicella-zoster virus, as well as Toxoplasma and syphilis.
To memorize the timing of pathological periods, use the GBEF rule: Gametopathy (before conception), Blastopathy (up to 15 days), Embryopathy (up to 75 days), Fetopathy (until birth).
Class and exam questions
Can a diagnosis of prematurity be made based on weight alone?
No, a weight of less than 2,500 g is not the sole criterion. Approximately one-third of full-term infants are born with such low birth weight.
What is the difference between neonatal and infant mortality?
Neonatal mortality accounts for the death of infants in the first 28 days of life, while infant mortality accounts for deaths within the first year.
What malformations are typical for fetopathies?
Fetopathies are characterized by the persistence of embryonic structures (e.g., patent foramen ovale, cleft lip) and organ hypoplasia (renal dysplasia, microcephaly).
What else to study on this topic
- Mechanisms of conjoined twin malformations
- Characteristics of TORCH infections in the fetus
- Morphology of hemolytic disease of the newborn
- Classification of gestosis and its effect on the placenta
Master the entire topic in the "Pathological Anatomy" course
This is a summary. The course covers everything tested in classes and exams.
- Complete study guide on "Perinatal Pathology" and 4,414 more pages of the subject
- Assignments and quizzes after every topic — just like in a colloquium
- AI tutor answers questions on the topic anytime
- 153 video lessons on the subject
Other topics in «Chapter 24. Childhood Diseases»
Free video lessons: pathological anatomyShort lessons with study notes — no registration required.
Prepared by WhiteCoat Pro faculty in accordance with the medical school curriculum. For educational purposes only.