What are Some of the Causes of SGA?

Patient Presentation
A 38 1/7 week gestation, newborn girl was delivered by normal spontaneous vaginal delivery, with Apgar scores of 8 at 1 minute and 9 at 5 minutes, to a 27 year old Hispanic mother with 1 previous living child. The past medical history was significant for the mother having close monitoring during the 3rd trimester because of symmetric small-for-gestational age (SGA) in the fetus. The mother’s other child was also SGA with a similar pattern and currently was a small but healthy 33 month old. The family history was positive for the mother’s sister who had an infant die in utero in the first trimester. There was diabetes and obesity in family. The family had a relatively shorter stature. The mother was average size for her family and was 5’1″, and the father was tall for his family and was 5’7″ with mid-parental height at 10-25%.

The pertinent physical exam at birth showed a small, thin infant with a wrinkled face and a lusty cry. Her weight was 2674 grams (5-10%), her length was 47.5 cm (10-25%) and her head circumference was 33 cm (10-25%) using World Health Organization growth charts. There were no obvious congenital abnormalities and she had a 3-vessel umbilical cord. She had thinner skin and smaller amounts of subcutaneous fat and musculature. Her Ballard examination was scored 34 (a score of 35 corresponding to a 38 week infant). The diagnosis of an infant with symmetric SGA was made. It was felt this was due to a constitutionally small infant.

The patient’s clinical course over the next several hours found that she had normal glucose tests when monitored on the neonatal glucose protocol. By discharge on day 2 of life the infant was feeding every 1-3 hours for about 30 minutes. She was having 2-3 wet diapers/day and had lost 113 grams or about a 4% decrease from her birth weight. At followup on day of life 5, she had continued to nurse well along with some formula supplements that had been given when the mother was sleeping. She had lost another 46 grams and had decreased 6% from her birth weight. Her mother felt that her milk had come in the day before. On followup at day 7 of life the infant had gained 33 grams since the previous visit, and at day 15 she was past her birth weight. She continued to be a smaller infant growing around the 10% for the first several months of life. At age 15 months she was around the 10-25% for weight, and 25% for height and head circumference and was growing appropriately.

Intrauterine growth retardation or fetal growth retardation is due to a pathological process that causes decelerated fetal growth velocity. Small-for-gestational age (SGA) is an infant with growth parameters below the normal range for gestational age. More commonly, SGA is defined as a birth weight < 10% for gestational age. This may be due a pathological or non-pathological process (e.g. constitutionally small fetus). Using these standards, remember that 10% of all infants will be < 10% for weight, and they do not necessarily have an underlying problem and infants who are constitutionally small do not have increased perinatal mortality and morbidity. SGA and IUGR are not synonymous. IUGR always refers to a pathological process, whereas SGA may or may not be a pathological process but just a small infant.

SGA infants classically appear small with thin, loose skin, little subcutaneous fat and decreased muscle mass. The umbilical cord is thin. The face has a shrunken or “wizened” appearance often. Therefore, the gestational age at birth is best determined by the neurological assessment than by the physical appearance.

Symmetric SGA usually reflects a fetal problem and usually occurs in the first trimester with overall growth restriction. The long-term prognosis is not as good as asymmetric SGA reflecting an increased risk underlying disease processes such as a genetic abnormality.

Constitutionally small infants usually have symmetric SGA.

Asymmetric SGA usually reflects a placental problem and usually occurs in the 2nd and 3rd trimesters with growth restriction that is discordant. Usually head circumference is preserved, with length somewhat affected, and weight affected the most.

The earliest gestational ultrasound scans are most accurate for recognition of SGA and especially for correct dating of the pregnancy. Special ultrasound growth curves are used which use initial maternal height and weight, ethnic origin, fetal gender and parity. Abdominal circumference is the most accurate ultrasound measurement to determine SGA.

“The recurrence risk for SGA is 29% if a previous pregnancy was affected and 44% if two previous pregnancies were affected.”

Learning Point
Causes of SGA include:

  • Genetic abnormalities
    • 5-20%
    • Can include: Aneuploidy, single gene mutations, genetic imprinting, partial deletions or duplications, uniparental disomy and other variations including multiple syndromes, (e.g. chondroplasias, growth hormone deficiency, Turner syndrome, etc.).
  • Congenital infection
    • 5-10%
    • Cytomegalovirus and toxoplasmosis are most common
    • Herpes, HIV, influenza malaria, parvovirus, rubella, syphilis, varicella, zika are other common infections
  • Structural problems
    • Often seen along with genetic abnormalities
    • Cardiac anomalies
    • Renal anomalies
  • Placental abnormalities
    • Confined placental mosasiacism
    • Placental growth factors
  • Maternal factors
    • Height, weight, age, parity, ethnicity
    • Maternal disease including hypertension, preeclampsia
    • Chronic maternal disease – inflammatory bowel disease, epilepsy
    • Lifestyle – smoking, alcohol or drug use, obesity
    • Social stressors
    • Multiple gestation
    • Incorrect pregnancy dating

SGA complications include:

  • Newborn
    • Asphyxia
    • Hypoglycemia
    • Immune function impairment
    • Polycythemia and hyperviscosity
    • Thermoregulation impairment
    • Mortality
    • Complications of underlying disease such as genetic, structural or infectious disease
  • Long-term
    • Growth problems especially in weight and height (although many infants will improve)
    • Neurodevelopmental problems
    • Adult disease including increased risk of coronary artery disease, hypertension, hyperlipidemia and chronic kidney disease

Questions for Further Discussion
1. What are common treatments given to, or monitored for, in SGA newborns?
2. What could be included in an evaluation for SGA?
3. What are common causes of large for gestational age (LGA) infants?

Related Cases

To Learn More
To view pediatric review articles on this topic from the past year check PubMed.

Evidence-based medicine information on this topic can be found at SearchingPediatrics.com and the Cochrane Database of Systematic Reviews.
Information prescriptions for patients can be found at MedlinePlus for this topic: Birth Weight

To view current news articles on this topic check Google News.

To view images related to this topic check Google Images.

To view videos related to this topic check YouTube Videos.

Vrachnis N, Botsis D, Iliodromiti Z. The fetus that is small for gestational age. Ann N Y Acad Sci. 2006 Dec;1092:304-9.

Finken MJJ, van der Steen M, Smeets CCJ, Walenkamp MJE, de Bruin C, Hokken-Koelega ACS, Wit JM. Children born small for gestational age: differential diagnosis, molecular-genetic evaluation and implications. Endocr Rev. 2018 Jul 4.

Mandy GT, Infants with fetal (intrauterine) growth restriction. UpToDate. (reviewed 6/29/18, cited 10/2/18).

Donna M. D’Alessandro, MD
Professor of Pediatrics, University of Iowa