- Fetal factors Causing IUGR.

 Fetal factors Causing IUGR

·     Constitutional: most of SGA infants are normal (genetically small)

·     Genetic causes (5-20%)

-        Chromosome anomalies include: Aneuploidy (like Trisomy 21, 18, 13, and 16), uniparental disomy (of chromosomes 6, 14, 16), partial deletions or duplications (Cri du chat syndrome, Wolf Hirschhorn syndrome), ring chromosome, and aberrant genomic imprinting. The finding of symmetric FGR prior to 20 weeks of gestation suggests aneuploidy as the cause, most commonly trisomy 18.

-        Single gene disorders such as Russell Silver syndrome, Bloom syndrome, Cornelia de Lange syndrome, and Fanconi anemia have been associated with FGR.

·       Congenital malformations (e.g., Cardiovascular anomalies, Congenital diaphragmatic hernia, abdominal wall defects (omphalocele and gastrochisis), renal agenesis or dysplasia, anencephaly, tracheoesophageal fistula, single umbilical artery, gastrointestinal atresia, Potter syndrome, anorectal malformation, and pancreatic agenesis)

·       Congenital infection (CMV and toxoplasmosis are the most common), the incidence is highest when infection occurs in the 1^st  trimester, CMV and rubella are associated with severe FGR.

·     IEM (e.g., galactosemia and phenylketonuria).

·     Insulin deficiency (production or action of insulin)

·     Insulin-like growth factor type I deficiency

 

 

- Ponderal index.

 

Ponderal index

The ponderal index (PI) is a useful tool to detect FGR, particularly in infants with asymmetric FGR.

PI is a ratio of body weight to length expressed as:

PI = [weight (in g) x 100] ÷ [length (in cm)]3

Ponderal index is recorded as a number in g/cm3, but there are also percentile curves for ponderal index.

Normal ponderal index is GA dependent, but is generally 2.2 to 3.0 g/cm3 (3rd and 97th percentile).

A ponderal index of <2 or <10% is abnormal and suggests asymmetrical FGR. Infants with constitutional or symmetric FGR typically have a normal ponderal index.

With normal growth, the PI increases gradually from 30 to 37 weeks gestation and then remains constant. Decreased growth of adipose tissue and skeletal muscle, the major contributors to body weight, results in a reduced PI. PI of less than the 10th percentile reflects fetal malnutrition; PI of less than the 3rd percentile indicates severe wasting.