Not all small babies are growth restricted. Some babies are healthy and constitutionally small.
Some babies are small because of an adverse effect such as intra uterine infection or exposure to some toxin early in pregnancy.
Most babies who have intrauterine growth restriction will do so because of placental insufficiency.
Small babies need very close monitoring.
Small babies are defined as being born with a birth weight of less than 3.0kg at 40 weeks gestation. This incorporates 10% of all births in Australia.
Intrauterine growth restriction is serious and has the potential to cause fetal harm. Fetal distress, emergency caesarean section and even cerebral palsy or worse can result from undiagnosed intrauterine growth restriction (IUGR). There are however special circumstances where growth restriction is more likely to occur and should be anticipated. A maternal history of having had a previous growth restricted baby strikes an alert and needs to be investigated.
Possible underlying factors that may be causing growth restriction need to be identified, treated and monitored closely. (Placental insufficiency, Hypertension, thrombophilias, Connective tissue disorders, Marginal cord insertion and Intra-uterine infection etc.).
Pregnancies complicated by IUGR need to be monitored closely and often the baby will need to be delivered earlier than expected if the risks become too high. The timing of delivery is based on balancing the risks of growth restriction against the risks of prematurity.
Unfortunately no test for fetal growth assessment is perfect. Within the limits of error Obstetricians should focus on fetal growth and well being as a priority. The objective is to prevent a baby coming to harm.
Intrauterine growth restriction is divided into two groups:
- Asymmetrical growth restriction
- Symmetrical growth restriction
These two categories actually have different aetiologies.
Asymmetrical Growth restriction
Asymmetrical Growth restriction is much more common and is ultimately the result of poor placental vascular function.
This cause for poor placental function will have many factors including:
- antiphospholipid syndrome,
- other blood clotting disorders
- uterine abnormalities
- illicit drug use etc.
Thrombophilias include a series of blood clotting conditions that will cause small blood vessels to clot. It is obvious to everyone that the function of the placenta is to provide the fetus with adequate food and oxygen to ensure fetal well being. Any thrombosis of placental vessels will result in decreasing placental blood flow. This will result in potentially serious harm to the fetus if not monitored.
Investigations would include:
- Anticardiolipin antibodies
- Lupus anticoagulant
- B1 Glycoprotein 2
- Factor V Leiden mutation
- Antithrombin III
- Prothrombin 20210 mutation
- Protein S & C deficiency
- Methylene tetrahydro folate reductase deficiency (MTHFR)
- Antinuclear antibody
- Extractable nuclear antigens (ENA)
If no cause can be identified for a previous growth restricted baby it would be appropriate to treat the patient in her next pregnancy with a combination of:
- Low dose aspirin (LDA 100mg aspirin). CLASP study.
- Higher dose Folate intake.
- Vitamin D and Calcium supplements
If a thrombophilia is identified, it will be necessary to treat the patient in the current pregnancy with Clexane, a blood thinning injection that needs to be injected daily by the patient for most of the pregnancy.
Monitoring of placental function is essential and will involve a series of high quality ultrasounds monitoring fetal growth but more importantly placental and middle cerebral artery doppler blood flow patterns.
Other parameters of fetal well-being are also assessed by performing a biophysical profile score.
If a level of deterioration in fetal well being is reached, it will become necessary to plan the delivery of the baby. If prematurity is an issue then it will be necessary to administer steroids to stimulate fetal lung maturity and Magnesium Sulfate infusion for cerebral protection.
Symmetrical growth restriction
Symmetrical growth restriction is less common but is often caused by an early insult to the pregnancy. This may be caused by:
- Fetus with a chromosomal abnormality.
- Non-chromosomal syndromal conditions.
- Transplacental infection (TORCH screen).
- Drug treatment for some pre-existing medical disorder in the mother.
Symmetrical growth restriction poses extra concerns regarding the question of continuing with the pregnancy.
In many circumstances an amniocentesis will need to be performed (including microarray assay) and sometimes a geneticist consultation.
Intrauterine infections are suspected on blood tests (serial serology and reactive lymphocytosis). It can be diagnosed when an amniocentesis is performed at 20 weeks and in certain cases treatment with hyper immune immunoglobulin (antibody) treatment can be offered to protect the fetus.
In any event in those pregnancies where after appropriate consultation the patient continues with her pregnancy, very close monitoring of fetal growth, brain growth and placental function is essential.
Given the limits of error in available testing, we should do our best to diagnose IUGR. In circumstances where a pregnancy is compromised by growth restriction the pregnancy will be investigated and the baby will be closely monitored. The mother will be kept well informed of progress and her management options will be discussed. The ultimate objective is to prevent the baby from coming to harm. The baby may require early delivery.