Hypoplastic type

• early onset
• symmetric, organ weights ratios normal
• the infant appears small with normal bodily proportions
• Related to chromosomal disorders, congenital anomalies, intrauterine infections (the TORCH group, syphilis) and other teratogens. Administration of teratogens during the organogenesis interrupts critical phase of organ developement and produces malformations in addition to retarding growth throughout the body. Administration of teratogens after the period of organogenesis causes growth retardation only.

Malnutrition type

• late onset  —  unusual before 20 weeks of gestation
• asymmetrical form, disturbance of organ weight ratios
• sparing of brain growth at the expense of skeletal muscle and internal organs
• the head is disproportionally large
• the skin may be wrinkled with meconium staining
• oligohydramnios
• the causes of this type of growth retardation are reduced uteroplacental perfusion (preeclampsia, chronic hypertension, placenta previa, heavy maternal smoking ) or chronic maternal undernutrition

Other causes of growth failure

• confined placental mosaicism  —  genetic abnormality limited to the placenta (trisomies frequent) is found in 2% of viable pregnancies affected by fetal growth restriction, the fetus is normal but small
• babies from multiple gestations are of lower birthweight than singletons
• parenatal habitus (small women tend to have small babies) or race may be responsible for SGA, but this is not pathologic