Abnormal fetal development. The diseases of the fetus. Amniotic membranes and placenta

By their significance in medicine the anomalies of a fetus development and congenital diseases are comparable to such widespread diseases as illnesses of heart and vessels, tumor, infection. The problem of infertility, miscarriages, neonate morbidity, and perinatal death is connected to this problem.

The reasons of occurrence of developmental anomalies and many fetus diseases are complicated and still are not completely investigated. The anomalies of placenta and membrane development are neither fully studied.

It is known that causes of development of inherent anomalies are the following:
- Hereditary factors;
- Influence of damaging factors of external environment (ionizing radiation, intoxication, effect of poisoning substances, chemical agents);

- Complications of pregnancy and labor: the prolonged and severely proceeding hestoses, endocrinological diseases during pregnancy, acute infectious and viral diseases (cytomegaly, rubella, hepatitis, toxoplasmosis, etc.), chronic hypoxia of the fetus.

- Effect of medicinal substances (antibiotic drugs, antiparasitic drugs, anticoagulants of indirect action, preparations of testosterone and some other hormones, аntimetabolites, etc).

In different periods of intrauterine life of the fetus, the damaging factors render unequal action. In clinical practice the division of prenatal ontogenesis into four periods is most common: progenesis, blastogenesis, embriogenesis, fetogenesis. In its turn, fetogenesis is divided into early and late fetogenesis. Each period is characterized by specific forms of pathology, the knowledge of which helps to estimate their reasons.

The pathology of progenesis includes all changes, which have occurred in gametes. The damaging factors can produce effect during laying, forming and ripening of gametes. The basic pathology of gametes causing the disturbances of intrauterine development is mutation, i.e. changes of hereditary structures. Genetic, chromosomal and genomic mutations are distinguished.

The pathology of blastogenesis is limited to the first 15 days after fertilization. To the basic results of blastopathy the following refer: empty embryonic sacs formed due to aplasia or early destruction and subsequent resorption of embrioblast, hypoplasia and aplasia of amnion, amniotic peduncle, yolk sac, paired defects of development (completely or partially not divided twins).

A greater part of embryos damaged due to blastopathy are eliminated by spontaneous abortions, more often in 3-4 weeks after fetus’ death.

The pathology of embryogenesis is limited to 8 weeks, since the 8th day and until the 10th week after fertilization. All kinds of pathology of embryo occurring under the influence of damaging factors in this period are called embriopathies. Embriopathies are manifested by disturbances of organ formation, which result in destruction of embryo or congenital defects of development.

The pathology of fetogenesis includes the time of intrauterine development, beginning with the 11th week of gestation and up to delivery. In this period a further differentiation of tissues and ripening of fetus’ organs occur, and the formation of placenta is finished (approximately by the 12th week of gestation). All kinds of fetus’ pathology developing in this period are called fetopathies. The fetal period is divided into early (till the 28th week of pregnancy) and late (since the 28th week of pregnancy). Accordingly, the early and late fetopathies are distinguished.

Anomalies of Development of Fetus. Fetal Diseases. Anomalies of Development of Fetus. The congenital defect of development means persistent morphological changes of an organ or organism beyond the limits of their possible structure, causing its dysfunctions. They occur in intrauterine period due to disturbances of developmental processes of embryo or (rarer) after birth of child due to disturbances of further formation of organs (e.g., tooth defects, persisting arterial duct, arrest of development of organ or whole organisms).

The following disturbances of development refer to the congenital defects:

Aplasia — a complete congenital absence of organ or its part. The absence of some parts of organ is sometimes termed by a word originated from Greek "oligos" (small) and the name of damaged organ. For example, "oligodaktilia" — absence of one or several fingers, "oligogiria" — absence of some gyri of cerebrum.

Congenital hypoplasia — underdevelopment of organ manifested by deficiency of relative weight or size of organ. A simple and displastic form of hypoplasia are distinguished. Simple hypoplasia, as compared to displasia, is not accompanied by structural disorders of organ. Congenital hypoplasia also means reduction of weight of the whole body of newborn or fetus.

Congenital hypertrophy (hyperplasia) is an increased relative weight (or size) of organ. Macrosomia (gigantism) — an increased length and weight of a fetus’ body. Sometimes hyperplasia is termed by the word "pachis" (thick). For example, "pachygiria" — thickened gyri of the brain, "pachyacria" — thickened phalanges of fingers.

Heterotopia — availability of cells, tissues or whole areas of organ in another organ or areas of the same organ, where they should not be. Such displacements of cells and tissues are usually revealed under a microscope.

Heteroplasia — a disturbed differentiation of some types of tissues, e. g. presence of cells of flat epithelium in Meckel’s diverticulum. Heteroplasia should be distinguished from metaplasia — a secondary change of differentiation of tissues, usually connected with chronic inflammation.

Ectopia — displacement of organ, i.e. its location in an unusual place, e. g. location of kidney in the pelvis, location of the heart outside the chest.

Doubling — (doubling of uterus, a double arch of aorta) — presence of additional organs (polydaktyly, polysplenia, etc).

Atresia — a complete narrowing of canal or natural aperture.

Stenosis — narrowing of canal or aperture.

Non-division (fusion) of organs (or twins). The undivided twins are called “pagus”, adding a Latin term denoting the place of connection. For example, the twins united in the area of thorax, are called “thoracopagus”, in the area of skull — “craniopagus”, etc. The name of defects of not divided extremities or their parts begin with prefix syn, sym (from Greek together) — “syndactylia”, “sympodia” (unity of fingers, feet respectively).

Persistence — preservation of embryonic structures, normally disappearing by a definite period of development (nonclosure of ductus Botalli or foramen ovale in a 3-month or older child).

Congenital defects are differentiated according to:
- etiologic sign,
- sequence of origin in organism,
- time of effect of teratogenic factor,
- localizations.

By etiological sign, three groups of congenital defects are distinguished:
- inherited,
- exogenous,
- multifactor.

To congenital anomalies the defects refer which have occurred due to mutation, i.e. stable changes in the material of gametes. Depending on level of mutation the gene and chromosomal inherited defects are distinguished.

To exogenous anomalies the congenital defects of development refer conditioned by damage with teratogenous factors directly of embryo or fetus.

To defects of multifactor etiology the disorders refer caused by joint effect of genetic and exogenous factors, neither of which individually is the reason of defect.

Depending on sequence of formation in organism, the primary and secondary congenital defects are distinguished.

- The primary defects of development are directly caused by influence of teratogenic factor (genetic or exogenic).

- The secondary defects are complications of primary defects and are always pathogenetically connected with them, being “defects of defects". For example, аtresia of aqueduct of cerebrum, resulting in hydroencephalus, is a primary defect, and hydrocephalus — a secondary one.

According to time of effect of teratogenic factor blastopathies, embryopathies, fetopathies (late and early) are distinguished.

According to localization, congenital defects are subdivided into those of:
- central nervous system
- face and neck
- cardiovascular system
- respiratory system

- organs of gastrointestinal system
- skeletomuscular system
- urinary system
- genital organs
- endocrine glands
- skin and its appendages
- other defects.