Synonyms: IUGR, intrauterine growth retardation, fetal growth restriction, FGR
Intrauterine growth restriction (IUGR) is a condition where a baby's growth slows or ceases when in it is in the uterus.
It is part of a wider group - small for gestational age (SGA) fetuses - which includes fetuses that have failed to achieve their growth potential and fetuses that are constitutionally small.
Approximately 50-70% of fetuses with a birthweight below tenth centile for gestational age are constitutionally small. The lower the centile for defining SGA, the greater the likelihood of IUGR. On the other hand, a fetus with growth restriction may not be SGA.
If the mother is small, it may be normal for her to have a small fetus; this is constitutional SGA, not IUGR.
Causes of IUGR can be maternal, placental or fetal.
- Increasing maternal age.
- Hypertension or heart disease.
- Diabetes in pregnancy including gestational diabetes.
- Maternal alcohol abuse causing fetal alcohol syndrome or fetal alcohol effects.
- Maternal use of other drugs including cannabis.
- Maternal smoking (causes 30-40% of cases - if quit before 15 weeks should be normal).
- Renal disease in pregnancy.
- Undiagnosed coeliac disease.
- Drugs including warfarin, phenytoin and steroids.
- In many cases of IUGR, the placenta is small and doesn't provide sufficient nutrition to the growing baby. In IUGR pregnancies, blood flow to the placenta decreases as pregnancy progresses, compared with normal pregnancy when blood flow to the placenta increases throughout pregnancy to meet the growing baby's demand for oxygen and nutrition.
- Cell death (apoptosis); in pregnancies complicated by IUGR, the placenta contains a relatively high proportion of cells that have a shorter life than normal. This means the placenta functions less well, thereby transferring fewer nutrients and less oxygen both to and from the baby.
- In multiple pregnancy, one or more fetuses is often small. Twins show IUGR in 15-20% of cases.
- Chromosomal abnormalities including Down's syndrome, Edwards' syndrome, Patau's syndrome and Turner's syndrome.
- Congenital defects are associated with SGA.
- Intrauterine infection such as cytomegalovirus, toxoplasmosis, rubella and syphilis.
- When the problem is placental insufficiency, the head is not as restricted in size as the abdominal girth - head sparing. This represents preferential nutrition to the brain, with a lack of glycogen stored in the liver.
- If there is a fetal problem such as a chromosome abnormality, there is uniform restriction of growth.
There may be racial differences. Babies of Indian race tend to be a little smaller. If the fetus is in the lower centiles but continues to grow within those centiles, this is reassuring but, if growth is slow and the fetus is falling into lower centiles, this is cause for concern.
Risks associated with intrauterine growth restriction
There is increased risk of:
- Intrapartum fetal distress.
- Intrapartum asphyxia.
- Postnatal hypoglycaemia or hypocalcaemia-neonatal complications.
- Impaired neurodevelopment.
- Meconium aspiration.
- Intrauterine death.
- Possibly type 2 (non insulin-dependent) diabetes and hypertension in adult life.
The reason that studies on SGA fetuses have shown poor perinatal outcome is likely to be the high incidence of true IUGR in this group. However, the vast majority of term SGA infants have no appreciable morbidity or mortality.
Physical examination of the abdomen by inspection and palpation detects as little as 30% SGA fetuses. Therefore, if SGA is suspected, it is necessary to supplement abdominal palpation with ultrasound.
Correct assessment of gestational age is essential and so an ultrasound examination in the first trimester should be routine.
Symphyseal fundal height (SFH) measurement has limited diagnostic accuracy to predict an SGA neonate. A large study found the sensitivity and specificity to be 27% and 88% respectively. Serial measurements may improve sensitivity and specificity.
Antepartum surveillance should be instituted once the possibility of extrauterine survival for the growth-restricted fetus has been determined. This may include Doppler scanning, stress or non-stress testing, and amniotic fluid volume assessment biophysical profile (BPP).
The use of Doppler ultrasonography to measure umbilical artery waveforms should be considered a part of fetal evaluation once IUGR is suspected or diagnosed. Modern techniques give very accurate information. The triplex mode is used to assess umbilical venous blood flow. There is a colour Doppler picture of the umbilical vein, pulsed Doppler velocimetry, and real-time ultrasound to measure the diameter of the umbilical vein.
- An elevated ratio of femoral length to abdominal circumference (AC).
- An elevated ratio of head circumference (HC) to AC.
- Unexplained oligohydramnios.
The AC measurement is the best single measurement to assess fetal growth because, where growth is restricted, the liver is usually affected. AC and estimated fetal weight (EFW) are the most accurate diagnostic measurements to predict SGA.
Oligohydramnios is an indicator of IUGR. Amniotic fluid of less than 5 cm, as measured in the four quadrants, is suggestive of oligohydramnios. Other causes of oligohydramnios include death in utero, renal agenesis, and premature rupture of membranes.
There is evidence that it is the trend (growth) that is of more value in predicting poor fetal outcome.
When a small fetus is diagnosed, the risk of chromosomal defects should be assessed; up to 19% of fetuses with an AC and EFW less than the fifth centile may have chromosomal defects. The risk is higher when growth restriction is associated with structural abnormalities, a normal liquor volume or a normal uterine or umbilical artery Doppler. Therefore, all growth-restricted fetuses need an ultrasound anatomical survey as a minimum. It may also be appropriate to offer karyotyping.
Definitive management depends on the cause:
- If the cause is constitutional, there is no cause for alarm and pregnancy can continue as normal.
- Detailed ultrasound examination may show features of chromosome abnormalities. By the time that diagnosis is made, it is probably too late for termination of pregnancy, but the parents can be apprised of what to expect.
- If the problem is placental inadequacy, the risks of delivery versus prematurity have to be balanced.
- Umbilical artery Doppler to monitor high-risk fetuses (growth-restricted) reduces perinatal morbidity and mortality.
- The biophysical profile has not been shown to improve perinatal outcome but sufficient data do not exist to rule out its value. A Cochrane review found only four poor-quality studies with fewer than 3,000 patients. Authors of the review concede that to make a meaningful conclusion about the impact of biophysical profile on perinatal mortality, in excess of 10,000 women would need to be studied.
When to deliver?
The Growth Restriction Intervention Trial (GRIT) showed there is no evidence that early delivery to pre-empt severe hypoxia and acidosis reduces any adverse outcome. However it appeared that obstetricians currently make appropriate delivery decisions to minimise mortality.
- When end diastolic flow is present in the umbilical artery, delay delivery until at least 37 weeks, provided other surveillance findings are normal.
- When end diastolic flow is absent or reversed, admission, close surveillance and administration of steroids are required. Among preterm growth-restricted fetuses with absent end-diastolic blood flow in the umbilical artery, the umbilical artery/middle cerebral artery ratio is the best predictor of neonatal mortality or severe morbidity. If other surveillance results (biophysical profile, venous Doppler) are abnormal, delivery is indicated. If gestation is over 34 weeks, even if other results are normal, delivery may be considered.
- Administer steroids if gestation is between 24+0 and 34+6 weeks. Antenatal steroids significantly reduce the incidence of respiratory distress syndrome.
- Intrapartum monitoring with continuous cardiotocograph is recommended.
- Deliver in a unit where optimal neonatal expertise and facilities are available. A skilled resuscitator who is trained and competent in resuscitation of the newborn should be present at delivery.
- Where possible, an experienced neonatologist should be present if gestation is extremely preterm or growth restriction is severe.
- Babies that have been starved in utero tend to be hungry and feed enthusiastically to gain weight. As an adult they can expect normal or only slightly reduced stature.
- If there was slow head growth before 26 weeks they may show significant developmental delays at 4 years of age. It has also been shown to be associated with impaired executive cognitive function in young adults.
- An extremely low birth weight implies a high risk of perinatal mortality and neonatal morbidity, but the most significant variable that can be correlated to the long-term neurological outcome is the gestational age.
- Studies have shown that infants with birth weight below 2.5 kg have a three times increased risk of death due to coronary artery disease later in life. There seems to be an increased risk of hypertension, type 2 diabetes, and autoimmune thyroid disease.
Further reading & references
- Saving Mothers' Lives. Reviewing maternal deaths to make motherhood safer: 2006-2008; Centre for Maternal and Child Enquiries (CMACE), BJOG. Mar 2011
- Ott WJ; The diagnosis of altered fetal growth. Obstet Gynecol Clin North Am. 1988 Jun;15(2):237-63.
- Chard T, Costeloe K, Leaf A; Evidence of growth retardation in neonates of apparently normal weight. Eur J Obstet Gynecol Reprod Biol. 1992 Jun 16;45(1):59-62.
- 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.
- McCarthy FP, Khashan AS, Quigley E, et al; Coeliac disease. Don't forget increased risk of fetal growth restriction. BMJ. 2009 Mar 17;338:b1069. doi: 10.1136/bmj.b1069.
- 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.
- Taylor DJ, Howie PW; Fetal growth achievement and neurodevelopmental disability. Br J Obstet Gynaecol. 1989 Jul;96(7):789-94.
- Roth S, Chang TC, Robson S, et al; The neurodevelopmental outcome of term infants with different intrauterine growth characteristics. Early Hum Dev. 1999 May;55(1):39-50.
- 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.
- Barker DJ; The long-term outcome of retarded fetal growth. Clin Obstet Gynecol. 1997 Dec;40(4):853-63.
- Gardosi J, Mul T, Mongelli M, et al; Analysis of birthweight and gestational age in antepartum stillbirths. Br J Obstet Gynaecol. 1998 May;105(5):524-30.
- Jones RA, Roberton NR; Small for dates babies: are they really a problem? Arch Dis Child. 1986 Sep;61(9):877-80.
- Hall MH, Chng PK, MacGillivray I; Is routine antenatal care worth while? Lancet. 1980 Jul 12;2(8185):78-80.
- Rosenberg K, Grant JM, Tweedie I, et al; Measurement of fundal height as a screening test for fetal growth retardation. Br J Obstet Gynaecol. 1982 Jun;89(6):447-50.
- Persson B, Stangenberg M, Lunell NO, et al; Prediction of size of infants at birth by measurement of symphysis fundus height. Br J Obstet Gynaecol. 1986 Mar;93(3):206-11.
- Pearce JM, Campbell S; A comparison of symphysis-fundal height and ultrasound as screening tests for light-for-gestational age infants. Br J Obstet Gynaecol. 1987 Feb;94(2):100-4.
- The Investigation and Management of the Small-for-Gestational-Age Fetus, Royal College of Obstretricians and Gynaecologists (2002)
- Snijders RJ, Sherrod C, Gosden CM, et al; Fetal growth retardation: associated malformations and chromosomal abnormalities. Am J Obstet Gynecol. 1993 Feb;168(2):547-55.
- Alfirevic Z, Neilson JP; Doppler ultrasonography in high-risk pregnancies: systematic review with meta-analysis. Am J Obstet Gynecol. 1995 May;172(5):1379-87.
- Alfirevic Z, Neilson JP. Biophysical profile for fetal assessment in high risk pregnancies. Cochrane Review; February 1996
- Thornton JG, Hornbuckle J, Vail A, et al; Infant wellbeing at 2 years of age in the Growth Restriction Intervention Trial (GRIT): multicentred randomised controlled trial. Lancet. 2004 Aug 7-13;364(9433):513-20.
- 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.
- Gerber S, Hohlfeld P, Viquerat F, et al; Intrauterine growth restriction and absent or reverse end-diastolic blood flow in umbilical artery (Doppler class II or III): A retrospective study of short- and long-term fetal morbidity and mortality. Eur J Obstet Gynecol Reprod Biol. 2006 May 1;126(1):20-6. Epub 2005 Aug 31.
- Spinillo A, Montanari L, Bergante C, et al; Prognostic value of umbilical artery Doppler studies in unselected preterm deliveries. Obstet Gynecol. 2005 Mar;105(3):613-20.
- Vergani P, Roncaglia N, Locatelli A, et al; Antenatal predictors of neonatal outcome in fetal growth restriction with absent end-diastolic flow in the umbilical artery. Am J Obstet Gynecol. 2005 Sep;193(3 Pt 2):1213-8.
- Soll R, Ozek E; Prophylactic protein free synthetic surfactant for preventing morbidity and mortality in preterm infants. Cochrane Database Syst Rev. 2010 Jan 20;(1):CD001079. doi: 10.1002/14651858.CD001079.pub2.
- Intrapartum care, NICE Clinical Guideline (2007)
- CESDI; Enquiry into sudden unexpected deaths in infancy
- Tideman E, Marsal K, Ley D; Cognitive function in young adults following intrauterine growth restriction with abnormal fetal aortic blood flow. Ultrasound Obstet Gynecol. 2007 Jun;29(6):614-8.
- Valcamonico A, Accorsi P, Sanzeni C, et al; Mid- and long-term outcome of extremely low birth weight (ELBW) infants: An analysis of prognostic factors. J Matern Fetal Neonatal Med. 2007 Jun;20(6):465-71.
- Gortner L; Intrauterine growth restriction and risk for arterial hypertension: a causal relationship? J Perinat Med. 2007 Jul 12;.
- Shankaran S, Das A, Bauer CR, et al; Fetal origin of childhood disease: intrauterine growth restriction in term infants and risk for hypertension at 6 years of age. Arch Pediatr Adolesc Med. 2006 Sep;160(9):977-81.
- Jansson T, Powell TL; Role of the placenta in fetal programming: underlying mechanisms and potential interventional approaches. Clin Sci (Lond). 2007 Jul;113(1):1-13.
|Original Author: Dr Hayley Willacy||Current Version: Dr Hayley Willacy|
|Last Checked: 16/07/2010||Document ID: 2336 Version: 22||© EMIS|
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