Small for gestational age babies (SGA babies) are smaller or less developed than most babies of their gestational age and gender. In such a case, the baby’s birth weight is below the 10th percentile compared to babies of the same gestational age.
Birth weight may vary in babies, and several factors can result in low birth weight in babies. However, low or high birth weight is considered normal if it falls within a specific range.
Read on to learn more about SGA babies, reasons for low birth weight, and how to manage it.
What Is Small For Gestational Age?
Small for gestational age (SGA) refers to a baby whose birthweight is less than the 10th percentile for babies’ weight at the same gestational age (1). It means the baby’s weight is less than 90% of other babies of the same gestational age.
Gestational age refers to the number of weeks of pregnancy (2). For example, if a baby is born after 40 weeks of pregnancy and their birth weight is less than 90% of babies born after 40 weeks of pregnancy, he/she is considered small for gestational age.
Small for gestational age is a comparative measurement that helps a doctor determine the newborn’s overall health. A small for gestational age baby could be premature, post-term, or full-term. SGA babies could be small due to normal reasons or have underlying pathology.
What Causes A Baby To Be SGA?
There could be several reasons why a baby could be small for gestational age. Some babies are SGA due to hereditary, where the baby is small because their parents happen to be short in stature (3). Such babies may not display complications during fetal life or at birth.
Most babies are SGA because they experience intrauterine growth restriction (IUGR), a condition where the fetus does not receive adequate oxygen and nutrients for optimum growth, causing them to be smaller than normal (4). Several factors could increase the risk of IUGR and SGA.
Risk Factors For SGA
Below are various factors that increase the risk of IUGR, leading to an increased risk of the baby being born small for gestational age (5) (6). These factors may also directly cause the baby to be SGA without causing IUGR.
1. Maternal factors
These factors affect the mother and, in turn, affect the baby.
- High blood pressure
- Chronic kidney disease
- Heart disease
- Respiratory condition
- Severe anemia
- Maternal lifestyle choices; use of tobacco, alcohol, or narcotics
2. Fetal factors
These conditions affect the fetus.
- Birth defects
- Chromosomal abnormalities
3. Pregnancy-related factors
These factors affect the placenta or uterus and may or may not be due to maternal or fetal problems.
- Poor blood flow to the uterus and placenta
- Detachment of the placenta from the uterus
- Incorrect position of the placenta
- Presence of multiple fetuses (twins or triplets)
How Is SGA Diagnosed?
The doctor could diagnose small fetal size and IUGR through ultrasonography. The healthcare provider will perform the fundal height measurement where the distance from the woman’s pubic bone to the fundus (top of the uterus) is measured (1). If the fundal height is low, it could indicate that the fetus is small and could be born small for gestational age.
Postnatal checkups can determine SGA through assessment of weight. The doctor may also check other parameters, such as head circumference, to confirm the diagnosis.
Small For Gestational Age Chart
The chart denotes the 10th percentile birth weight in grams for different gestational ages in weeks (pregnancy in weeks). A baby with a birth weight less than the 10th percentile birth weight could be considered small for gestational age (7).
|Gestational age (weeks)||Boys 10th percentile (grams)||Girls 10th percentile (grams)|
Source: Fenton charts, University of Calgary
Note: The normal birth weight for gestational age may vary due to several factors, including the country you reside. Therefore, speak to a doctor to determine the precise small for gestational age weight in your region.
What Are The Complications Of SGA?
A few SGA babies may not display any complication and are normal at birth. They may have smaller organs but with normal functions. The doctor may still keep the baby under observation for some hours to days, depending on the baby’s health.
SGA complications at birth
- Low blood oxygen
- Low blood sugar
- Poor body temperature regulation
- Meconium aspiration syndrome
- Excess red blood cells (Polycythemia)
- Low Apgar score
Long-term SGA complications
- Behavioral problems
- Metabolic disorders
- Poor learning abilities
- Neurological dysfunctions
- Poor academic performance
How Are SGA Babies Treated?
There is no way to bring the baby to a normal weight immediately after birth. The doctor may recommend a wait-and-watch technique with periodic review of the baby’s weight. SGA babies with no complications may catch up on their growth and attain a normal development pattern between the ages of six and 24 months (10).
SGA babies with complications could require treatment, which may depend on several factors, such as the extent of birthweight’s deviation from the 10th percentile, baby’s health at birth, and presence of congenital problems. The type and duration of treatment could vary depending on the complications.
Babies with severe complications may require intravenous medications or nutrition, enteral nutrition (feeding through feeding tubes), or incubator support with a ventilator. The baby may require frequent checkups to diagnose or rule out long-term complications. Nearly 85% of SGA babies achieve normal growth patterns by 24 months.
How To Prevent SGA?
The risk of having an SGA baby could be reduced through appropriate prenatal care. You may observe the following measures during pregnancy for adequate care and early detection of any problems.
- Timely ultrasounds checks as per recommended schedule
- Appropriate diet during pregnancy
- Maintain healthy gestational weight
- Take prescribed supplements, such as folic acid and iron
- Avoid unhealthy habits, such as smoking and alcohol use
You may improve health before conception to reduce the chances of complications. A few ways to improve health are maintaining a healthy weight and quitting unhealthy habits. There is no way to avoid fetal and maternal genetic anomalies. Timely ultrasound checks may help determine any signs of genetic problems in the fetus. You may seek the help of a genetic counselor before conception if you or your partner have genetic problems or if either of you has a family history of congenital defects.
Frequently Asked Questions
1. What is the difference between IUGR and SGA?
IUGR stands for intrauterine growth restriction, a condition where the fetus is smaller than normal due to maternal, fetal, or pregnancy-related factors. The term small for gestational age or SGA refers to a baby whose weight is less than the 10th percentile for babies’ weight at the same gestational age. IUGR may cause a baby to be SGA, but not all SGA babies experience IUGR as a fetus (8).
2. Can SGA babies be normal?
Yes. SGA babies may be constitutionally normal if their birth weight is consistent with expected optimal birth weight. These babies do not face any risk of morbidity or mortality (11).
3. Do SGA babies sleep more?
A study on 75,531 mother–child dyads suggested that SGA babies had shorter sleep duration. However, future studies are required to investigate the importance of sleep patterns in babies with gestation-related conditions (12).
4. What are the differences between SGA and preterm infants?
SGA babies have a birth weight below the 10th percentile for gestational age, while preterm babies have been delivered before 37 weeks of gestation. SGA babies may be preterm or full-term (13).
5. Do SGA babies move less?
A study conducted in 2020 measured the movement of fetuses using a fetal movement acceleration measurement recorder. The results suggested that SGA babies had less fetal movement, even without hypoxia (14).
SGA babies appear smaller than the 10th percentile compared to other babies of the same gestational age. It could be genetic or due to maternal and fetal factors; pregnancy-related complications could also be the cause. SGA babies with no complications may catch up on their growth rapidly; however, those with problems may require treatment, depending on the complication. By the age of 24 months, most SGA babies are on track with normal growth. But, continue to monitor your baby’s growth milestones and seek medical advice if you have any concerns.
- Small for gestational age helps doctors determine the newborn’s overall health.
- Maternal factors, fetal factors, and pregnancy-related factors may cause the baby to be SGA.
- Some SGA babies may not display any complications, while in others, they could manifest at birth or at later stages.
- The risks of delivering an SGA baby can be reduced by taking proper prenatal care.
2. Small for Gestational Age; Stanford Children’s Health
3. Small for Gestational Age (SGA); Fairview
4. Small for Gestational Age; Children’s Hospital of Philadelphia
5. Small for gestational age (SGA); U.S. National Library of Medicine
6. Robert L. Stavis, Small-for-Gestational-Age (SGA) Infant; Merck Manuals
7. Fenton Preterm Growth Charts; University of Calgary
8. IUGR/SGA; The University of British Columbia
9. Ester Maria Lundgren and TorstenTuvemo, Effects of being born small for gestational age on long-term intellectual performance; U.S. National Library of Medicine
10. Won Kyoung Cho and Byung-KyuSuh, Catch-up growth and catch-up fat in children born small for gestational age; U.S. National Library of Medicine
11. Obiyo O. Osuchukwu and Danielle J. Reed; Small for Gestational Age; NCBI; (2022)
12. Mari Hysing et al.; Sleep Duration and Nocturnal Awakenings in Infants Born with Gestational Risk; NCBI; (2019)
13. Alfa Muhihi et al.; Risk factors for small-for-gestational-age and preterm births among 19,269 Tanzanian newborns; NCBI; (2016)
14. Masayoshi Morita et al.; Counting fetal movements of small-for-gestational infants using a fetal movement acceleration measurement recorder; NCBI; (2020)