Fetal growth

Fetal growth is associated with intense somatic and functional changes

• Growth = quantitative acquisition of body weight
• Development = qualitative changes associated with cell and tissue differentiation of individual organ systems and their subsequent functional maturing

Insulin + IGF-1 (Insulin-like growth factor 1) = main growth factors during fetal development and early postnatal period

Prenatal Period

• Pre-embryonic phase (fertilised egg to nidation/implantation)
• Embryonic phase (conception to 8 weeks – organogenesis)
• Fetal phase (8 weeks to the end of intrauterine period – tissue/organ growth and development)

Factors affecting Fetal Growth

Constitutional

Genetic abnormalities

• chromosomal aberrations
• trisomies (Down syndrome => 47XX +21 for females and 47XY + 21 for males)

Congenital infection

• syphilis (Treponema pallidum)
• toxoplasmosis (Toxoplasma gondii)
• rubeola
• cytomegalovirus (CMV)
• herpes simplex
• parvovirus B19

Maternal diseases

• too young/old age (primipara vetus)
• single mothers
• malnutrition
• smoking and alcohol abuse
• drug abuse (risk for neonatal abstinence syndrome)
• previous uterine interventions
• multiple birth
• recurrent abortions
• history of preterm birth
• chronic illness (hypertension, diabetes mellitus, autoimmune diseases)
• pregnancy complications (preeclampsia, HELLP syndrome = Hemolysis, Elevated Liver enzymes, Low Platelets)

Placental/Amniotic disorders

• acute/chronic placental insufficiency (hemorrhage, small placenta, placenta praevia, abruption, degenerative changes in placenta)
• polyhydramnios
• premature rupture of membranes
• chorioamnionitis
• funisitis

These factors intertwine with the risk factors of preterm birth in general, i.e. many times infants are born premature and are smaller (multiple birth, intrauterine growth restriction, congenital anomalies, etc).

Fetal biometry = ultrasound measurement of fetal anthropometric parameters and fetal weight calculation; monitoring of fetal development and fetal movements; can detect congenital anomalies.

Pregnancy (months)	Fetal Weight (grams)	Fetal Length (cm)
6	650	30
7	1150	35
8	1800	40
9	2700	45
10	3500	50

Intrauterine growth restriction

Intrauterine Growth Restriction (IUGR) = reflects chronic malnourishment based on chronic hypoxia and malnutrition (placental dysfunction) or stems from fetal disorder

• Fetal weight < 10^th percentile for given gestational age and gender
• Growth restriction progresses in this order => weight => length => head circumference

Small for gestational age newborn is then a result of intrauterine suboptimal conditions (birth weight < 10^th percentile for given gestational age and gender). There are generally 2 types of infants who suffered from IUGR (hypotrophic newborns):

• Asymmetric (begins in the last trimester => low birth weight, normal length and head circumference)
• Symmetric (begins earlier => low birth weight, as well as length and head circumference)

Features of IUGR infants

• for term, hypotrophic infants, the postnatal adaptation is usually without complications
• thin/absent subcutaneous fat layer
• thermal instability
• metabolic complications (hypoglycemia, hypocalcemia, hypomagnesemia)

Hypoglycemia may require frequent feeding or parenteral nutrition (to provide sufficient glucose infusion rate => 5-8 mg/kg/min, or higher)

• polycythemia
• dermatology findings in case of congenital infection (exanthema, petechiae)
• increased risk for perinatal mortality
• increased risk for adverse neurodevelopment (due to chronic hypoxia and extrauterine growth restriction = EUGR) => requires handling, physiotherapy, appropriate stimulation
• failure to thrive (if unable to do “catch-up” growth) => if weight remains < 3^rd percentile at 2 years of age => endocrinology assessment and possible growth hormone administration

Macrosomia

Macrosomia = reflects increased fetal weight – constitutional; maternal diabetes mellitus; fetal hydrops (erythroblastosis fetalis); congenital heart defects; Beckwith-Wiedemann syndrome

• Fetal weight > 90^th percentile for given gestational age
• Large for gestational age newborn as a result of macrosomia (birth weight > 90^th percentile for given gestational age)
• Increased risk for perinatal complications (birth trauma), postnatal complications (hypoglycemia, polycythemia)

References

① Kiserud T, Benachi A, Hecher K, et al. The World Health Organization fetal growth charts: concept, findings, interpretation, and application. Am J Obstet Gynecol. 2018;218(2S):S619-S629. doi:10.1016/j.ajog.2017.12.010