The Role of Infections in Intrauterine Growth Restriction (IUGR)
Intrauterine growth restriction is diagnosed when the birth weight falls below the 10th percentile for the current gestational age. Intrauterine infections (cytomegalovirus infection, toxoplasmosis, herpes, rubella) are classified among the fetal causes of IUGR and result in its most severe form.
Infectious fetal injury leads to the development of the hypoplastic (symmetrical) variant of IUGR:
- Timing: The pathological changes originate in the early stages — during the 1st and 2nd trimesters of pregnancy.
- Morphology: There is a symmetrical lag in all parameters (body weight, length, and head circumference). The absolute number of cells in organs is reduced, and reserves of glycogen and adipose tissue are decreased proportionally.
- Complications: Such newborns have a critically increased incidence of asphyxia, hypothermia, hypoglycemia, and secondary infectious complications in the postnatal period.
Endocrine disorders in growth pathology
Normal fetal growth is regulated by specific hormones, the balance of which can be disrupted in infectious and placental pathologies:
- Insulin and insulin-like growth factors (IGFs): Play a key role. Insulin is synthesized by the fetus itself (does not cross the placenta), ensuring fat and glycogen accumulation as well as protein synthesis. IGFs stimulate the cell cycle. In intrauterine malnutrition, the level of C-peptide in fetal blood is frequently decreased.
- Growth hormone (somatotropin): Does not affect physical growth in utero, as the fetal receptor apparatus has not yet formed.
- Thyroid hormones: Do not determine body weight, but are absolutely essential for proper differentiation and maturation of cellular structures.
Intrauterine hypoxia and aspiration syndrome
Against the background of an infectious process (e.g., placental inflammation), placental insufficiency frequently develops, leading to intrauterine hypoxia. Oxygen deprivation triggers a cascade of pathological reactions:
- Metabolic shifts: Tissue glycolysis is intensified, glycogen is depleted, and severe acidosis develops.
- Hemodynamics: Following a transient spike in blood pressure, vascular tone drops. Generalized venous congestion occurs, vascular permeability increases, leading to edema and multiple diapedetic hemorrhages (subarachnoid hemorrhages are particularly characteristic).
- Fluid aspiration: Hypoxia irritates the respiratory center, causing the fetus to make deep respiratory movements. Concurrently, irritation of the vagus nerve (n. vagus) stimulates bowel motility, releasing meconium into the amniotic fluid.
Lung morphology in aspiration: Lanugo hairs (lanugo), epithelial scales, and meconium clumps are found in the lumens of the bronchi and alveoli. If hypoxia occurred in the setting of a maternal infection (endometritis, vaginitis, chorioamnionitis), the amniotic fluid becomes infected. In such cases, microscopic examination of the fetal lungs reveals a massive presence of microorganisms and maternal leukocytes. For comparison: during the aspiration of non-infected fluid, the fetal reaction is different — macrophages appear after 12–16 hours, while neutrophils appear only on the second day.
Impact on lung development (RDS)
Chronic intrauterine hypoxia, IUGR, and infections exhaust the fetal compensatory mechanisms, increasing the risk of respiratory distress syndrome (RDS) — hyaline membrane disease.
Its essence is surfactant deficiency, which is normally synthesized by type 2 pneumocytes. Up to 32–34 weeks, synthesis proceeds via the imperfect ethanolamine methylation pathway, which is extremely sensitive to hypoxia and acidosis. When surfactant is deficient, the alveoli collapse (atelectasis), the endothelium is damaged, and fibrinous exudate accumulates in the alveoli. It forms homogeneous eosinophilic films — hyaline membranes — that completely block gas exchange, closing the vicious cycle of hypoxemia.
Briefly: answers to topical questions
What pathways of surfactant synthesis exist in the fetus, and at what gestational ages do they function?
There are two main pathways of surfactant synthesis in the fetus, functioning at different stages of gestation.
- The ethanolamine methylation pathway is the primary pathway until 32–34 weeks of intrauterine development. It is imperfect and easily depleted during hypoxia, acidosis, or hypothermia.
- The choline pathway becomes active at later stages of pregnancy.
Synthesis begins at 20–24 weeks, when surfactant is detected in trace amounts. From 24 weeks, the activity of producer cells increases rapidly, reaching peak synthetic activity by 35 weeks.
What morphological changes in the placenta are characteristic of intrauterine infections?
Intrauterine infections are characterized by the development of inflammatory processes in various placental structures, depending on the route of infection.
- Villitis is inflammation of the villi (focal or diffuse, exudative or proliferative), which is the main indicator of hematogenous infection. The chronic process leads to sclerosis of the villous stroma and obliteration of fetal vessels.
- Chorioamnionitis is focal or diffuse leukocyte infiltration of the extraplacental membranes in ascending infection.
- Funisitis is inflammation of the umbilical cord vessels (initially veins, then arteries), complicated by thrombosis.
In specific infections (e.g., listeriosis), foci of necrosis and granulomas form in the villous stroma.
What specific malformations does the rubella virus cause in the fetus?
The rubella virus causes multiple congenital malformations in the fetus. The classical triad includes:
- Cataracts.
- Deafness.
- Heart defects.
Also, congenital rubella is characterized by eye lesions, including chorioretinitis, and CNS involvement. Meningoencephalitis and impaired myelination processes have been described in the CNS. CNS damage combined with deafness and blindness leads to mental retardation.
To remember the profile of symmetrical IUGR (infectious): "Symmetry is a System." The entire organism is affected systemically from early stages, so everything is reduced proportionally.
Class and exam questions
Which infections cause IUGR in the fetus?
The main pathogens leading to growth restriction include cytomegalovirus (CMV), rubella virus, herpes simplex virus, and Toxoplasma.
What is the difference in the lungs between the aspiration of infected and uninfected amniotic fluid?
Upon aspiration of infected amniotic fluid (in the setting of chorioamnionitis), microbes and maternal leukocytes are immediately detected in the lungs. In sterile aspiration, an endogenous macrophagic reaction occurs first (after 12–16 hours), while neutrophils appear later.
How do infections affect the development of hyaline membranes?
Infections are often accompanied by fetal hypoxia and acidosis. These conditions deplete the immature enzyme systems of type 2 pneumocytes, suppressing surfactant synthesis, which directly leads to atelectasis and hyaline membrane formation.
Which hormone is critically important for fetal growth, but does not cross the placenta?
This is insulin. The fetus must secrete it independently. Its deficiency or impaired receptor sensitivity leads to severe intrauterine growth restriction.
What else to study on this topic
- Pathogenesis and morphology of the hypotrophic (asymmetric) variant of IUGR
- Mechanisms of hyaline membrane formation in neonatal RDS
- Effect of maternal diabetes mellitus (hyperinsulinemia) on surfactant maturation
- Morphological signs of post-term pregnancy and placental insufficiency
- Chromosomal and gene diseases as fetal causes of IUGR
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 the topic "Intrauterine Infections" and 4,414 more pages on 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.