Fetal growth is primarily influenced by three factors
More than 40% of the variation in the birth weight is due to genetic factors while the remaining is from environmental factors. Under normal circumstances it grows into a healthy appropriate sized newborn seizing its inherent potential.
These factors are further elaborated as under:
“Tall Parents have tall children”. Parental traits are generally transmitted to the offspring.
The structure of the chest and fatty tissue has better genetic association than other somatic characteristics.
Thyroxine and insulin have an important role in regulating tissue accretion and differentiation in fetus. Thyroxine is secreted in human fetus from the 12th week of gestation.
Growth hormone though present in high levels in fetus is noth known to influence fetal growth.
Fetal growth factors
These factors can be both growth promoting and growth inhibitory. A large number of growth factors are synthesized locally in fetal tissues. Their prime effect is on cell division.
Fetal weight directly correlates with placental weight at term. With advancing gestation the weight of the placenta increases to cater to the increased needs of the baby. This positive remodeling facilitates nutrient transport across the placenta.
The mothers own fetal and childhood growth and nutrient intake and body composition at the time of conception and during pregnancy play an important role in determining fetal size.
Some negatively influencing factors are advanced age or teenage pregnancy and anemia. Smoking of tobacco, drug and alcohol abuse retard fetal growth and induce complications. These complications may take the form of hypertension and multiple pregnancies produce fetal growth restriction. Chronic systemic disease and acquired infections also may influence fetal growth.