Small for Gestational Age (SGA) refers to a baby whose birth weight and/or length is below a specific measurement for their gestational age. This typically means their size falls below the 10th percentile when compared to other babies born at the same number of weeks of pregnancy. SGA is a descriptive measurement at birth, rather than a specific medical diagnosis or disease. It indicates the baby was smaller than expected for their age in the womb.
Expected Growth Trajectories for SGA Babies
Following birth, many SGA infants often demonstrate “catch-up growth.” This is a period of accelerated growth where the baby rapidly gains weight and height, aiming to reach a size more typical for their age. This rapid growth usually begins shortly after birth and is most pronounced during the first 6 to 12 months of life. Most catch-up growth is generally completed by the time the child reaches two years of age.
About 85% to 90% of SGA infants achieve catch-up growth and enter the normal range on standard growth charts by their second birthday. Parents often observe their child growing at a faster pace than average during their early months. This accelerated growth helps these infants close the size gap with their peers, moving their measurements into higher percentiles.
Factors Influencing Postnatal Growth
The reasons a baby is born small for gestational age can impact their postnatal growth. Some infants are constitutionally small, due to genetic factors inherited from their parents and are otherwise healthy. Other babies are small due to intrauterine growth restriction (IUGR), a condition where the fetus did not receive adequate nutrients or oxygen in the womb, often linked to placental insufficiency or maternal health conditions.
Babies with IUGR may have higher caloric and protein requirements after birth to fuel catch-up growth and recover from nutritional deficits. Providing adequate nutrition, sometimes requiring at least 110-135 kcal/kg/day, is important for these infants to achieve growth rates similar to those experienced in utero. Breastfeeding is encouraged, as it supports optimal growth patterns, though fortified milk may be considered to meet increased needs.
When Catch-Up Growth Does Not Occur
While many SGA infants experience catch-up growth, approximately 10% to 15% do not achieve this accelerated growth. For these children, persistent short stature is a concern, defined as remaining below the 3rd percentile for height, or below -2.5 SDS by age two, or below -2 SDS by ages three to four years. If a child consistently fails to catch up, further medical evaluation may be recommended to investigate other conditions affecting their growth.
For children born SGA who continue to have short stature despite adequate nutrition and monitoring, growth hormone (GH) therapy may be considered. This treatment is typically initiated when a child is between two and four years of age, especially if they show no signs of catch-up growth over six months. The aim of GH therapy is to help these children achieve a height within the normal range, reaching an adult height suitable for their genetic potential.
Medical Monitoring and Management
Regular medical monitoring is important for SGA infants to track their postnatal growth patterns. Pediatricians record the baby’s height, weight, and head circumference on standardized growth charts during routine visits. These charts serve as a visual tool to assess whether a child is following an expected growth curve, including catch-up growth patterns.
Consistent tracking helps healthcare providers identify if a child is not growing as anticipated or if their growth deviates from a healthy trajectory. If a child’s height remains below the 2.5th percentile at two years of age, or below the 2nd percentile around three to four years, a pediatrician may recommend a consultation with a specialist. A pediatric endocrinologist, specializing in hormone-related growth issues, can provide further evaluation and guidance for these specific growth concerns.