From the Guidelines
Small for Gestational Age (SGA) is defined as a fetus whose estimated fetal weight (EFW) is below the 10th percentile for gestational age, while Intrauterine Growth Restriction (IUGR) refers to a pathological process that restricts a fetus from achieving its growth potential due to placental insufficiency or other factors. The key difference between SGA and IUGR is that SGA is a statistical definition based solely on size, while IUGR implies an underlying pathological process 1. Not all SGA babies have IUGR, as some are constitutionally small but healthy. Diagnosis involves serial ultrasound measurements tracking fetal growth parameters, with IUGR typically showing asymmetric growth patterns (head sparing with reduced abdominal circumference) and abnormal Doppler studies of umbilical and fetal vessels 1. Some of the key points to consider in the diagnosis and management of SGA and IUGR include:
- The use of population-based fetal growth references to determine fetal weight percentiles 1
- The importance of serial umbilical artery Doppler assessment to assess for deterioration 1
- The role of antenatal corticosteroids in promoting fetal lung maturation 1
- The need for close monitoring of infants with SGA or IUGR after birth for complications like hypoglycemia, polycythemia, and hypothermia 1. Management depends on severity and gestational age, including increased surveillance with twice-weekly non-stress tests and weekly biophysical profiles, antenatal corticosteroids if preterm delivery is anticipated, and timing delivery appropriately 1. For mild cases at term, vaginal delivery may be attempted, while severe early-onset IUGR may require cesarean delivery 1. The distinction between SGA and IUGR matters clinically because IUGR babies face higher risks of perinatal mortality and long-term neurodevelopmental issues compared to constitutionally small SGA infants 1.
From the Research
Definition of SGA and IUGR
- Small for Gestational Age (SGA) is defined as a birth weight less than two standard deviations below the mean or less than the 10th percentile of a population-specific birth weight for specific gestational age 2.
- Intrauterine Growth Restriction (IUGR) is defined as a rate of fetal growth that is less than normal in light of the growth potential of that specific infant 2.
- SGA and IUGR are often used interchangeably, but there are minute differences between them, with IUGR referring to a restriction in fetal growth and SGA referring to a birth weight that is below a certain percentile 2.
Diagnosis of SGA and IUGR
- Diagnosis of SGA is based on birth weight, with a weight below the 10th percentile considered SGA 3.
- Diagnosis of IUGR is based on evidence of abnormal growth, including arrest of growth or a shift in its rate measured longitudinally, with at least two measurements, 3 weeks apart 3.
- Ultrasound measurements, including head circumference, abdominal circumference, and femur length, are used to estimate fetal weight and diagnose IUGR 3.
Management of SGA and IUGR
- Management of SGA and IUGR includes close monitoring of fetal growth and well-being, as well as timely delivery if necessary 3.
- Corticosteroids may be recommended for women with an FGR fetus, and magnesium sulphate may be prescribed for preterm deliveries 3.
- Referral to a Level IIb or III maternity ward may be proposed in cases of severe FGR or SGA 3.
- Initial management of an SGA newborn includes combatting hypothermia, ventilation, and close monitoring of capillary blood glucose 3.
Long-term Complications of SGA and IUGR
- Children born with SGA or IUGR are at higher risk of minor cognitive deficits, school problems, and metabolic syndrome in adulthood 3, 4.
- SGA children who experience rapid catch-up growth and marked weight gain are at increased risk of premature adrenarche, early puberty, polycystic ovary syndrome, insulin resistance, and obesity 4.
- Neurodevelopmental outcomes are better in SGA infants with spontaneous catch-up growth 4.