Synonyms: light-for-date babies

Introduction

Small for gestational age (SGA) babies are those weighing ≤2500 g if born at term. They fall into 2 groups:

• Babies whose growth at all gestational ages has been low. They are light-for-dates, but otherwise healthy.
• Growth is normal in the early part of pregnancy, but slows in utero by at least 2 measurements, normally ultrasound. This is due to intrauterine growth restriction (IUGR). They have a wasted appearance with little subcutaneous fat. They are at greater risk of dying.

The very low birthweight (VLBW) baby weighs ≤1500 g.

Significance of SGA

SGA fetuses are at greater risk of:

• Stillbirth.
• Intrapartum hypoxia.
• Neonatal complications.
• Impaired neurodevelopment.
• Possibly type 2 (non-insulin-dependent) diabetes and hypertension in adult life.^1,2,3,4

However, the vast majority of term SGA infants have no appreciable morbidity or mortality.⁵

Epidemiology

Incidence

7% of neonates are of low birthweight. 10% weigh ≤2500 g.⁶

Risk factors

• Maternal age ≤17 years or ≥35 years.
• Socioeconomic class IV or V.⁷
• Weight before pregnancy ≤50 kg or ≥75 kg.⁸
• Smoking⁹ - although quitting before 15 weeks' gestation may negate risk.¹⁰
• Excessive consumption of alcohol.¹¹
• Drug/substance abuse.
• Previous low birthweight baby.
• Anaemia in pregnancy.
• Chronic hypertensive disease.¹²
• Maternal polycystic ovarian syndrome.¹³
• Antepartum haemorrhage.
• Multiple pregnancy.
• Congenital fetal defects.
• Intrauterine infection.

Diagnosis

There is a variety of methods used to detect small for gestational age (SGA) fetuses:

• Abdominal palpation (the least accurate).
• Measurement of symphyseal fundal height.
• Ultrasound - estimated fetal weight.
• Ultrasound - biophysical profiling.
• Ultrasound - Doppler flow velocimetry.

However, the following should not be forgotten:

• Most investigations use a one-off measurement (size) to predict SGA, while there is evidence that it is the trend (growth) that is of more value in predicting poor fetal outcome.
• All require an accurate estimation of gestation as a prerequisite for accuracy.
• Most tests diagnose SGA fetuses, rather than growth-restricted fetuses.
• Little allowance is made for important prognostic factors for SGA, such as maternal height, weight, ethnicity, parity and fetal gender.

Management

Antenatal

• If an SGA fetus is found, there should be a careful ultrasound survey for chromosome defects. Karyotyping may be offered.¹⁴
• The fetus should be monitored with umbilical artery Doppler. A study comparing fetal heart-rate monitoring, biophysical profile and umbilical artery Doppler found that only umbilical artery Doppler had value in predicting poor perinatal outcomes in SGA fetuses.¹⁵ Absent or reversed end diastolic flow is associated with increased perinatal mortality and morbidity.^16,17
• Timing delivery is a balance between Doppler findings and gestation. If the fetus is less than 36 weeks' gestation, the mother should receive corticosteroids.
• The fetus should be delivered in a unit with neonatal expertise and facilities.

Intrapartum

• Continuous electronic fetal monitoring should be offered.¹⁸
• There is currently no evidence to support routine elective Caesarean delivery.^19,20

Post-delivery

• Care should either be provided for in a nursery temperature >24°C or, for very small babies, in an incubator at a temperature of 26-32 °C and humidity 65-75%.
• Temperature is decided by monitoring the infant's core temperature and adjusting accordingly.
• Oxygen is supplied either by a head box or into the incubator:
  • The level is adjusted according to monitoring by transcutaneous oxygen electrode or pulse oximetry.
  • A level is maintained that avoids hypoxia, but also considers the problem of toxicity on the retina (retinopathy of prematurity (ROP)).²¹
• Infection control is important:
  • Careful attention should be paid to avoiding overcrowding and the possibility of medical attendants or relatives introducing infection into the nursery.
  • Hands must be washed before handling a baby.
• Feeding should start 6 hours after birth, using breastmilk as soon as possible:
  • Normally, the baby is fed by nasogastric tube or spoon.
  • They are put to the breast as soon as they are suckling strongly.
  • If the baby is unable to accept enteral feeding then may need to supplement with parenteral nutrition.
  • Regularly check for hypoglycaemia and treat with IV glucose if necessary.
• Supplements of vitamin A, C, D, niacin and riboflavin are also given.²²
• If Ca²⁺ <2 mmol/L, give calcium gluconate IV slowly.
• Cranial ultrasound (to detect haemorrhage)

Complications

• Spontaneous preterm delivery.²³
• Respiratory distress syndrome.
• Cyanotic attacks - caused either by inadequate ventilation or cerebral damage.
• Jaundice.
• Hypoglycaemia - affects 15% of cases.
• Hypocalcaemia - usually occurs in the first 24 hours of life.
• Intracranial haemorrhage - mainly occurs in babies weighing <1500 g.
• Retinopathy of prematurity and sequelae.²⁴
• Cerebral palsy.^25,26

Prognosis

• Mortality increases with decreasing weight.⁶
• Preterm, low birthweight infants have an extremely high risk of mortality in their first year and parents should be counselled regarding this risk.²⁷

Very low birthweight (VLBW) females catch up in growth by 20 years of age whereas VLBW males remain significantly shorter and lighter than controls.²⁸

Morbidity

See separate article where this is covered: Premature Babies and their Problems.

Document references

1. McIntire DD, Bloom SL, Casey BM, et al; Birth weight in relation to morbidity and mortality among newborn infants. N Engl J Med. 1999 Apr 22;340(16):1234-8. [abstract]
2. Cnattingius S, Haglund B, Kramer MS; Differences in late fetal death rates in association with determinants of small for gestational age fetuses: population based cohort study. BMJ. 1998 May 16;316(7143):1483-7. [abstract]
3. Barker DJ; The long-term outcome of retarded fetal growth. Clin Obstet Gynecol. 1997 Dec;40(4):853-63.
4. Sallout B, Walker M; The fetal origin of adult diseases. J Obstet Gynaecol. 2003 Sep;23(5):555-60. [abstract]
5. Jones RA, Roberton NR; Small for dates babies: are they really a problem? Arch Dis Child. 1986 Sep;61(9):877-80. [abstract]
6. Doyle W; Maternal nutrition and low birth weight. J Fam Health Care. 2002;12(6 Suppl):2. [abstract]
7. Saving Mothers’ Lives 2003-2005 (Full report), Centre for Maternal and Child Enquiries
8. Cnattingius S, Bergstrom R, Lipworth L, et al; Prepregnancy weight and the risk of adverse pregnancy outcomes. N Engl J Med. 1998 Jan 15;338(3):147-52. [abstract]
9. Carter S, Percival T, Paterson J, et al; Maternal smoking: risks related to maternal asthma and reduced birth weight in a Pacific Island birth cohort in New Zealand. N Z Med J. 2006 Jul 21;119(1238):U2081. [abstract]
10. McCowan LM, Dekker GA, Chan E, Stewart A, Chappell LC, Hunter M, Moss-Morris R, North RA; SCOPE consortium. Spontaneous preterm birth and small for gestational age infants in women who stop smoking early in pregnancy: prospective cohort study. BMJ. 2009.
11. SIGN. (2003) The management of harmful drinking and alcohol dependence in primary care. Scottish Intercollegiate Guidelines Network.
12. Zetterstrom K, Lindeberg SN, Haglund B, et al; Chronic hypertension as a risk factor for offspring to be born small for gestational age. Acta Obstet Gynecol Scand. 2006;85(9):1046-50. [abstract]
13. Homburg R; Pregnancy complications in PCOS. Best Pract Res Clin Endocrinol Metab. 2006 Jun;20(2):281-92. [abstract]
14. The Investigation and Management of the Small-for-Gestational-Age Fetus, Royal College of Obstretricians and Gynaecologists (2002)
15. Chang TC, Robson SC, Spencer JA, et al; Identification of fetal growth retardation: comparison of Doppler waveform indices and serial ultrasound measurements of abdominal circumference and fetal weight. Obstet Gynecol. 1993 Aug;82(2):230-6. [abstract]
16. Soothill PW, Ajayi RA, Campbell S, et al; Prediction of morbidity in small and normally grown fetuses by fetal heart rate variability, biophysical profile score and umbilical artery Doppler studies. Br J Obstet Gynaecol. 1993 Aug;100(8):742-5. [abstract]
17. Karsdorp VH, van Vugt JM, van Geijn HP, et al; Clinical significance of absent or reversed end diastolic velocity waveforms in umbilical artery. Lancet. 1994 Dec 17;344(8938):1664-8. [abstract]
18. Intrapartum care, NICE Clinical Guideline (2007)
19. No authors listed; A randomised trial of timed delivery for the compromised preterm fetus: short term outcomes and Bayesian interpretation. BJOG. 2003 Jan;110(1):27-32. [abstract]
20. Haque KN, Hayes AM, Ahmed Z, et al; Caesarean or vaginal delivery for preterm very-low-birth weight (< or =1,250 g) infant: experience from a district general hospital in UK. Arch Gynecol Obstet. 2008 Mar;277(3):207-12. Epub 2007 Aug 11. [abstract]
21. Retinopathy of prematurity - UK guideline, Royal College of Ophthalmologists (2008)
22. Lucas A, Morley R, Cole TJ; Randomised trial of early diet in preterm babies and later intelligence quotient. BMJ. 1998 Nov 28;317(7171):1481-7. [abstract]
23. Morken NH, Kallen K, Jacobsson B; Fetal growth and onset of delivery: a nationwide population-based study of preterm infants. Am J Obstet Gynecol. 2006 Jul;195(1):154-61. [abstract]
24. O'Connor AR, Stewart CE, Singh J, et al; Do infants of birth weight less than 1500 g require additional long term ophthalmic follow up? Br J Ophthalmol. 2006 Apr;90(4):451-5. [abstract]
25. Mittendorf R, Pryde PG; Magnesium sulfate for the prevention of cerebral palsy. N Engl J Med. 2009 Jan 8;360(2):189-90; author reply 190.
26. Murphy DJ, Hope PL, Johnson A; Neonatal risk factors for cerebral palsy in very preterm babies: case-control study. BMJ. 1997 Feb 8;314(7078):404-8. [abstract]
27. Kristensen S, Salihu HM, Keith LG, et al; SGA subtypes and mortality risk among singleton births. Early Hum Dev. 2006 Jul 11. [abstract]
28. Hack M, Schluchter M, Cartar L, et al; Growth of very low birth weight infants to age 20 years. Pediatrics. 2003 Jul;112(1 Pt 1):e30-8. [abstract]

Internet and further reading

• Saving Mothers’ Lives 2003-2005 (Full report), Centre for Maternal and Child Enquiries
• NICE/Health Development Agency; Food-support programmes for low-income and socially disadvantaged childbearing women in developed countries, July 2006
• Ross MG et al; Fetal growth restriction, eMedicine, Feb 2010

Acknowledgements