Forms and causes of fetal growth restriction
In obstetrics, there are two main forms of this pathology, which differ in their time of onset and mechanisms of development:
- Symmetrical form: develops in early gestation (before 22 weeks) under the influence of chronic placental insufficiency and defective trophoblast invasion. A proportional reduction in the cellular elements of the fetus occurs.
- Asymmetrical form: develops in the second half of the gestational period against the background of impaired uteroplacental blood flow. In response to chronic hypoxia, centralization of circulation is activated—the bulk of the blood is directed to the brain to the detriment of other body parts.
Diagnostics: Ultrasound, Doppler ultrasonography, and cardiotocography
The main instrumental examination methods for pregnant women are ultrasound examination, Doppler ultrasonography, and cardiotocography.
- Ultrasonic fetometry: makes it possible to detect the lagging of abdominal dimensions relative to the head and femur in the asymmetrical form, as well as to assess the volume of amniotic fluid (oligohydramnios is frequently observed).
- Doppler ultrasonography: examines blood flow in the uterine arteries, umbilical artery, and middle cerebral artery. A decrease in the cerebroplacental ratio indicates the formation of a "protective circulatory circle".
- Cardiotocography (CTG): registers signs of chronic fetal hypoxia. A score of 5–7 points indicates initial disorders, while 4 points or less indicates pronounced hypoxia.
Pregnancy management and indications for delivery
There is no specific effective treatment for placental insufficiency, so the main goal of physicians is to prolong the pregnancy to a safe gestational age.
- Hospitalization is indicated for confirmed grade II–III FGR, blood flow disorders, or signs of hypoxia on CTG.
- Pharmacotherapy includes antiplatelet agents and low-molecular-weight heparins (especially in thrombophilia), as well as treatment of concomitant complications.
- Indications for preterm delivery: grade III FGR, absence of fetal growth for two weeks, critical hemodynamic disorders, or progressive hypoxia.
- The choice of method depends on the severity of the condition: in compensated forms, vaginal delivery is possible, whereas in grade III FGR, cesarean section becomes the method of choice.
Briefly: answers to topical questions
Which maternal infectious diseases can cause the development of the symmetrical form of FGR?
The symmetrical form of fetal growth restriction, which develops in early pregnancy, can be caused by various intrauterine maternal infectious diseases. Such infections include:
- Rubella
- Toxoplasmosis
- Herpes
- Syphilis
- Cytomegalovirus infection
These pathogens disrupt cellular growth processes and lead to a proportional reduction in all body dimensions of the fetus.
Which maternal extragenital pathologies are risk factors for the development of the asymmetrical form of FGR?
Risk factors for the development of the asymmetrical form of fetal growth restriction include maternal extragenital pathologies that lead to the formation of chronic placental insufficiency in the third trimester. Such conditions include:
- Hypertension
- Bronchial asthma
- Autoimmune diseases
These conditions cause impaired uteroplacental blood flow and chronic intrauterine hypoxia.
Which vascular resistance indices are used to calculate the cerebroplacental ratio?
To calculate the cerebroplacental ratio, vascular resistance indices in the arterial bed of the fetus and the umbilical cord are used. This parameter is calculated as the ratio of the following parameters:
- Resistance index in the middle cerebral artery (MCA)
- Resistance index in the umbilical artery
A decrease in this ratio indicates the centralization of circulation and the redistribution of fetal blood flow toward the brain during hypoxia.
What pathomorphological changes in the placenta underlie chronic placental insufficiency in FGR?
Chronic placental insufficiency in fetal growth restriction is based on pathomorphological changes that reduce the rate of metabolic processes across the placental membrane. Key changes include:
- Thickening of the placental barrier
- Collagen accumulation (in the basal layer)
- Accumulation of fibroblast processes (in the basal layer)
In addition, in the compensated form, involutive-dystrophic changes are observed, which are combined with compensatory reactions such as villous vascularization and the development of vasculosyncytial membranes.
FGR grades are easy to remember by the weeks of lag: Grade I — 2 weeks, Grade II — 3–4 weeks, Grade III — more than 4 weeks (as an escalation of severity from mild to critical).
Class and exam questions
What criteria are used to diagnose the symmetrical and asymmetrical forms of FGR?
The symmetrical form is determined by a uniform lag in fetometric parameters, taking into account the exact gestational age. The asymmetrical form is diagnosed by a decrease in abdominal circumference relative to the head and femur, when the head circumference to abdominal circumference ratio exceeds 1.0.
In which cases of fetal growth restriction (FGR) is early delivery by cesarean section indicated?
Surgical delivery is indicated for severe grade III FGR, lack of fetometric growth for two weeks, decompensated placental insufficiency with centralization of blood flow, and severe fetal hypoxia according to CTG data.
What is the phenomenon of centralization of fetal circulation?
This is a compensatory mechanism during hypoxia, in which the cerebral blood vessels dilate, and the main flow of arterial blood is directed to this vital organ due to reduced perfusion in other areas.
What else to study on this topic
- Pathogenesis and morphological changes of the placental barrier in chronic placental insufficiency
- Characteristics of the early neonatal period and respiratory distress syndrome in premature infants with hypotrophy
- Long-term consequences of FGR and the concept of "developmental origins of adult health and disease" (Barker hypothesis)
- Intranatal diagnosis of fetal hypoxia: Saling test, intrapartum CTG, and amniotic fluid index
- Initial neonatal resuscitation in the delivery room during asphyxia and Apgar scoring
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