The reasons behind the retarded development of foetuses are varied and not easily determined.
INTRA-uterine growth retardation (IUGR) is a condition in which a foetus is unable to achieve its genetically determined potential size. This has to be distinguished from small for gestational age (SGA) foetuses in which the growth is at the 10th or less percentile weight for all foetuses at a particular gestational age.
About 40% of SGA foetuses are constitutionally small; another 40% are at increased risk of preventable perinatal death; and the rest are small due to chromosomal or environmental causes, for instance, trisomy 18 and foetal alcohol syndrome.
IUGR occurs when nutrients and gas delivery to the foetus is insufficient to permit optimal growth. There may be maternal conditions that decrease oxygen carrying capacity, a dysfunctional oxygen delivery system due to maternal vascular conditions or placental damage due to maternal conditions.
The maternal factors that increase the risk of IUGR include pre-eclampsia, chronic hypertension, heart disease, diabetes, uterine malformations, smoking and substance abuse. The placental or umbilical factors that increase the risk of IUGR include multiple pregnancy, placenta praevia, abruptio placentae and abnormal cord insertion.
When the foetus has no nutritional reserve, it redistributes its blood flow to sustain the growth of vital organs, with increased relative blood flow to the brain, heart, adrenals and placenta, and decreased blood flow to the other organs. This is called the head sparing effect.
Growth may be symmetrical or asymmetrical. In the former, the foetus may have had an early global insult such as infection and foetal alcohol syndrome. The latter is more likely due to an imposed restriction on nutrient or gas exchange.
The symmetrical SGA infants have outcomes similar to those appropriate for gestational age. The asymmetrical SGA infants are more likely to have anomalies, pre-term birth, induction of labour before 36 weeks, Caesarean section for non-reassuring foetal heart rate, intubation in the labour ward, admission to neonatal intensive care unit, respiratory distress syndrome, intraventricular brain haemorrhage and neonatal death.
The consequences of IUGR extend into adult life with an increased risk of metabolic syndrome which is manifested as obesity, hypertension, cardiovascular disease, diabetes and hypercholesterolaemia. In addition, IUGR children have an increased risk of mental health problems.
The diagnosis of IUGR is not easy as there is no single test that provides an accurate diagnosis. As such, obstetricians screen foetuses during antenatal check-ups to identify those that are at risk. A useful population-wide screening test for IUGR is the fundal height measurement from the pubic symphysis. Although the sensitivity of fundal height measurement is limited, it is helpful in identifying potential IUGR.
An ultrasound scan at 16 to 20 weeks of pregnancy will confirm the dates, identify multiple pregnancy and evaluate for anomalies. Another scan at 28 to 32 weeks will detect abnormal growth, evidence of asymmetry and evidence of head sparing, that is, reduced amniotic fluid (oligohydramnios), abnormal Doppler findings.
Accurate gestational age and individual parameters measurements are available with the current ultrasound machines. An abdominal circumference measurement less than two standard deviations below the mean is a cutoff point to consider a foetus asymmetric.
Amniotic fluid volume measurements provide supporting evidence of a hostile intra-uterine environment. The incidence of IUGR is higher in those with a low amniotic fluid index or low maximum vertical pocket values.
Umbilical artery (UA) resistance shows a continuous decline in normal pregnancies but not in foetuses with uteroplacental insufficiency. The status of UA blood flow measured by Doppler corroborates the diagnosis of IUGR. It assists in the identification and initiation of surveillance of foetuses that are at increased risk of complications
Foetal medicine specialists carry out middle cerebral artery (MCA) Doppler studies. A normal MCA Doppler finding is useful in identifying SGA foetuses that are unlikely to have a major adverse outcome.
A meta-analysis of studies, where the goals were the treatment of impaired growth, reported three useful interventions:
> Cessation of smoking resulted in lower rate of low birth weight at term.
> Nutritional supplements in undernourished women and magnesium and folate supplementation, in some studies, resulted in a decrease in SGA babies.
> Where malaria is a cause, its treatment can increase foetal growth.
The only intervention shown to decrease neonatal morbidity and mortality is the administration of steroids to premature foetuses when delivery is anticipated. There is no evidence that hospital bed rest, maternal oxygen administration, maternal oestrogen administration and maternal nutritional supplements improve foetal growth or decrease perinatal morbidity and mortality.
Maternal haemodilution and intermittent abdominal negative pressure are experimental therapies and are potentially harmful to mother and foetus.
The management goal in a pregnancy diagnosed with IUGR is to deliver the most mature foetus in the best physiological condition possible with minimal risk to the mother. This involves a surveillance plan that maximises gestational age with minimal risks of neonatal morbidity and mortality. It requires antenatal testing with the hope of identifying the foetus with IUGR before it gets distressed in utero.
There are various protocols used in the management of IUGR. It is essential that the condition is managed by an obstetrician who is supported by a paediatrician, preferably a neonatologist, an anaesthetist and trained nursing staff. As the prognosis of severe IUGR is poor, its management is usually individualised.
The mode of delivery is dependent on the gestational age of the foetus, any foetal distress and the state of the cervix. An elective Caesarean section will be advised when there is evidence of foetal distress or there are traditional obstetrical indications.
When a trial of vaginal delivery is carried out, the foetal heart will be monitored and the mother nursed on her left side. Should there be any indication of foetal distress and the cervical state does not permit vaginal delivery, Caesarean section will have to be resorted to.
The cessation of smoking will result in a lower incidence of low birth weight at term. Although there are reports of the beneficial effects of aspirin, its role, if any, in the prevention of IUGR, is still unclear.
IUGR presents many challenges as it is not associated with risk factors in most instances and there is no single diagnostic test available. An obstetrician is usually alert to the possibility of IUGR. However, its diagnosis, assessment and management are complex.
Source: Dr Milton Lum