In plain words
Small for gestational age describes a baby who is smaller than expected for the number of weeks of pregnancy. The usual cutoff is below the 10th percentile on a growth chart for that gestational age. Some small babies are healthy and simply small, as is common with small parents. Others are small because the placenta is not supplying enough nourishment, which is called . Clinicians watch growth with ultrasound scans and fetal movement, and they look for the cause. A mother may hear this term after a scan shows a slow-growing baby, or after birth. Being small for gestational age is not the same as being premature, though the two can overlap. Follow-up depends on the cause and the baby's needs.
The deeper version
Small for gestational age is conventionally defined as birth weight below the 10th percentile for gestational age and sex on a population reference, with values below the 3rd percentile often described as severe. Many SGA infants are constitutionally small and have normal outcomes. SGA due to placental insufficiency, or fetal growth restriction, carries higher rates of perinatal morbidity and . Separating the two relies on serial ultrasound estimated fetal weight and abdominal circumference, umbilical artery Doppler, and the growth trajectory rather than a single measurement. Customized growth charts, which adjust for maternal size and ethnicity, have changed how SGA is identified in some settings. The consensus definition of fetal growth restriction (Gordijn and colleagues, 2016) is distinct from the descriptive term SGA.
Where it comes up
What mothers here say about small for gestational age
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Sources
- Gordijn SJ et al. — Consensus definition of fetal growth restriction: a Delphi procedure. Ultrasound in Obstetrics and Gynecology 2016
- American College of Obstetricians and Gynecologists — Practice Bulletin 204: Fetal growth restriction, 2019