While going through a chapter on IUGR, I came over an interesting fact. All time long, we have been thinking ' All IUGR babies are SGA but All SGA babies are not IUGR" . It is a common dictum we learn in medical schools, but the fact speaks something else. In a chapter written by Kara Calkins and Sherin Devaskar , the fact was very much well explained.
The fact is " All SGAs are not IUGR neither all IUGR are SGAs". An intrauterine growth restricted baby need not always be small for gestation but can be appropriate for gestation.
About the Basics,
SGA - Small for gestation age babies- babies whose birth weight is below the expected weight (< 10th centile) for gestation and sex.
AGA Appropriate for Gestation - Babies weighing between 10th to 90th Centile for expected gestation age at birth.
Intrauterine Growth restriction or IUGR are babies who fail to grow as per their growth potential due to intrauterine insults and can be SGA or AGA. Detection of IUGR relies on symphysis-fundal height measurements as part of routine prenatal care. Ultrasound is used to confirm IUGR based on estimated fetal weight and measurements of head & abdominal circumference.
Terminology : by ACOG : Defined as per pathology and Doppler changes
1. “SGA” refers to small fetuses with no discernible pathology and with normal umbilical artery and middle cerebral artery Doppler results.
2. “Growth restricted” refers to small fetuses with recognizable pathology and abnormal Doppler studies.
3. “Idiopathic growth restricted” applies to small fetuses with no discernable pathology or abnormal Doppler studies.
IUGR is basically a pathophysiological state where the fetus fail to reach their inutero growth potential. They must not be confused with SGA babies which can be constitutional, genetic or ethnicity related. More than babies born below 10 th centile in curves are constitutional and racial and do not pose added risk of further complications.
On the other hand , Intrauterine growth restricted babies who are born Appropriate for gestation age may have suffered intrauterine growth deceleration as a result of maternal or fetal factors. Even if these patient are mis-classified as AGA , they are not exempted from the complications that they are to face. Due to intrauterine survival mechanism, the natural response of the body is to preserve the brain and heart while rest of the organism gets compromised. Due to these intrauterine metabolic and physiological changes the infants are at risk of later diseases during infancy, pediatric period and adulthood.
The Careful attention, identification and follow-up of such babies become important.
Discussing the IUGR in details is beyond the scope of my discussion. A good short review of IUGR is given Here
1. Fanaroff and Martin's Neonatal perinatal medicine.