Causes of Reduced Fetal Growth (Fetal Growth Restriction)
Suboptimal perfusion of the maternal-placental circulation is the most common cause of fetal growth restriction, accounting for 25-30% of all cases, followed by chromosomal disorders and congenital malformations which are responsible for approximately 20% of cases. 1
Primary Etiologic Categories
Placental Causes (Most Common)
- Placental insufficiency due to suboptimal maternal-placental perfusion represents the leading cause, affecting 25-30% of FGR cases 1
- This typically manifests as late-onset FGR (>32 weeks gestation) with asymmetric growth patterns occurring in 70-80% of growth-restricted infants 2
- Placental dysfunction prevents adequate oxygen and nutrient delivery to the developing fetus 3
Fetal Causes
- Chromosomal disorders and congenital malformations account for approximately 20% of FGR cases 1
- Genetic imprinting disorders (such as Beckwith-Wiedemann syndrome and Silver-Russell syndrome) disrupt normal fetal growth mechanisms 4
- These typically present as early symmetric growth restriction 2
Maternal Factors
Constitutional and Demographic:
- Maternal age, weight, height, and race influence fetal growth potential 5
- Primigravida status and small maternal size increase risk 2
- Mother's own birth weight affects offspring growth 5
Nutritional Status:
- Poor maternal nutrition is a key factor, particularly in socioeconomic contexts 3, 5
- Maternal nutritional status before and during pregnancy directly affects nutrient availability to the fetus 3
Behavioral and Environmental:
- Active and passive tobacco smoking represents one of the most significant modifiable risk factors 5
- Alcohol and drug consumption during pregnancy 5
- Maternal stress levels and occupational factors (total working hours, time spent standing, physical activity) 5
Medical Conditions:
- Maternal hypertension and other vascular diseases 1
- Chronic maternal diseases affecting placental function 6
Uterine and Mechanical Factors
- Uterine malformations and uterine fibromata 2
- Oligohydramnios and multifetal gestation 2
- Early pelvic engagement of fetal head and aberrant fetal position 2
- These extrinsic biomechanical constraints typically arise during late gestation 2
Clinical Context and Diagnostic Considerations
When evaluating FGR diagnosed at <32 weeks of gestation, chromosomal microarray analysis should be offered for unexplained isolated cases 1. However, screening for toxoplasmosis, rubella, or herpes is not recommended in the absence of other risk factors, though PCR for cytomegalovirus should be performed in women with unexplained FGR who elect diagnostic amniocentesis 1.
Important Caveats
The distinction between true FGR and constitutional smallness is critical—true FGR represents pathological growth restriction where the fetus fails to reach its genetic potential, whereas some small-for-gestational-age infants are constitutionally small but healthy 1, 6. This differentiation has significant implications for surveillance intensity and delivery timing, as FGR carries substantially higher risks of stillbirth (1.5% for <10th percentile, up to 2.5% for <5th percentile) compared to appropriately grown fetuses 1.
Environmental and behavioral modifications, particularly smoking cessation and optimization of maternal working conditions, represent the most effective preventive strategies for reducing FGR incidence 1, 5.