A fetus is considered SGA when individual biometric measurements or a combination of measurements used to estimate fetal weight fall below set parameters and requires accurate assessment of gestational age.
Commonly, the definition of SGA refers to a fetus with a predicted weight or an abdominal circumference (AC) measurement less than the 10th centile. SGA at birth is commonly diagnosed based on a birthweight below the 10th centile and often birthweight charts are adjusted for the sex of the baby.
Fetal growth restriction (FGR) implies a pathological restriction of the genetic growth potential. Some, but not all, growth restricted fetuses/infants are SGA. The likelihood of FGR is higher in fetuses that are smaller. Growth restricted fetuses may manifest evidence of fetal compromise (abnormal Doppler studies, reduced liquor volume). Defining FGR and thus diagnosing it in a current pregnancy is challenging because of the need to determine growth potential. Similarly, risk assessing whether FGR existed in a previous pregnancy presents a different challenge. There is a need to focus on those fetuses at risk of adverse outcome and thus those that are FGR rather than SGA using varying parameters such as sequential ultrasound measurements, Doppler assessments, and biomarkers.
The purpose of this guideline is to provide advice that is based on the best evidence available to guide clinicians, regarding the investigation and care of the small–for–gestational age fetus and fetal growth restricted fetus. The guideline reviews the risk factors for these conditions and provides recommendations regarding surveillance, diagnosis, and management, including recommendations for fetal monitoring and birth.
Update July 2026: In December 2025 NHS England asked all maternity units in England to stop using Intergrowth 21 estimated fetal weight (EFW) charts (2000 or 2017 versions) due to concerns about their applicability in the NHS population. Analysis indicated that Intergrowth EFW charts could lead to a lower screen positive rate of small-for-gestational-age fetuses (<10th centile). This could mean that some fetuses that otherwise would have undergone enhanced surveillance had not. In response, the following update has been issued to the guideline: Correction to “Investigation and Care of a Small‐for‐Gestational‐Age Fetus and a Growth Restricted Fetus (Green‐top Guideline No. 31)” - BJOG: An International Journal of Obstetrics & Gynaecology - Wiley Online Library
COVID disclaimer
This guideline developed as part of the regular programme of Green-top Guidelines, as outlined in our document Developing a Green-top Guideline: Guidance for developers, and prior to the emergence of COVID-19.
Version history
This is the third edition of the guideline. The review process will commence in 2027, unless otherwise indicated.
Developer declaration of interests
Declarations of interest are stated within the guideline document.