Growth scans are becoming increasingly popular in maternity care - with many babies being induced early because they are either ‘too big’ or ‘too small’.

Woman can be confused by this, and feel their body has failed them.

Let’s focus for today, on the ‘too small’ baby, and when this is actually of concern, and why.

The first thing to understand is that babies who measure under the 10th percentile via ultrasound are labelled as ‘Small for Gestational Age’ or SGA - regardless of whether they are completely healthy and just genetically or constitutionally small, or whether they have been growth restricted due to a pathological process (usually placental problems, but can be other things) during the pregnancy.

Growth restricted babies have many neonatal complications, while healthy small babies usually adapt very well to extra-uterine life if supported physiologically. It is extremely important to distinguish the difference between healthy babies who are small, and unwell babies who have blood and nutrient restrictions which may result in them being small (it is important to note that normal sized babies can have these deficiencies also) - and a growth scan alone, will not identify this.

Failing to do this may result in unwell babies not being picked up, and well babies being interfered with unnecessarily.

Women who are labelled and managed as ‘high risk’ during pregnancy, develop unexpected complications or experience life-threatening emergencies for themselves or their babies report high levels of stress, trauma, helplessness, guilt and anxiety. Postnatally they are less likely to breastfeed, and more likely to experience postnatal depression. In these situations, it is even more important that a trusting, supportive and compassionate relationship with their care provider is maintained. In these situations, it is even more important that women, and their informed decision making rights, are held at the centre of emergency care.

Queensland Health (Queensland Clinical Guidelines 2016) defines fetal growth restriction (FGR) as an adaptive and initiatively protective process against a compromised state, which if left undiagnosed, can result in serious morbidity or mortality for mothers and babies. It occurs in around 10% of pregnancies. FGR is classified as either symmetrical or asymmetrical. Symmetrical FGR occurs early in the pregnancy and sees an overall reduction in size of the baby and is associated with chromosomal abnormalities, congenital conditions or infection; while asymmetrical FGR generally occurs later in gestation and sees a reduction in length and weight with a normal head size for gestational age. Asymmetrical FGR is the more common type, and is most commonly associated with placental problems and maternal conditions such as pre-eclampsia.

There is no cure for FGR.
Fetal weight measurement by ultrasound has an error rate of more than 10 percent, symphysis-fundal height measurement is unreliable and routine antenatal screening is not always possible. The use of growth charts or percentile cut offs do not consider pathophysiological processes, and alone may therefore be insufficient for discovering FGR babies, and inaccurate at differentiating between SGA and FGR.

The best tools for identifying the truly growth restricted baby is examination of fetal anatomy via ultrasound (there are tell-tale signs anatomically of malnutrition and oxygen deficiency) and uterine and umbilical artery doppler studies (measures how well the placenta is functioning). It is worth noting though, however false positive findings during an ultrasound could lead to unnecessary interventions and associated morbidity.

Growth restriction can result from hypertensive disorders (high blood pressure and/or pre-eclampsia) due to restricted blood flow and poor/small placental development, maternal age, health, smoking status and infection, while fetal factors include metabolism disorders and chromosomal abnormalities (less common). Babies rely on a functioning placenta to receive oxygen and nutrients.

Despite all the technological advancements. Normal fetal movements still remain one of the best clinical indicators we have of fetal wellbeing, which is why it is so important to stay connected to your baby.

Induction of labour is fairly common with the rationale of reducing stillbirth risk (there is alot more to this picture).

Truly growth restricted babies require continuous monitoring in labour, as they often experience fetal distress due to the normal hypoxic stress of uterine contractions (reduced blood flow and therefore oxygen during contractions) in combination with their placental insufficiency (not enough oxygen or nutrients to start with).

Induction of labour usually includes the use of synthetic oxytocin administration to stimulate uterine contractions, however this can result in hyper-stimulation of the uterus, not enough time between contractions for the fetus to recover and increases the likelihood of fetal distress from hypoxic stress.

Synthetic contractions are not able to consider the intricate hormonal communication between mothers and babies. Often in physiological birth we see ‘spacing’ of contractions, or less contractions, when a baby is compromised (the body knows much more than we do). This makes sense in an evolutionary sense, to give compromised babies more time between contractions to recover. This opportunity is not given to babies who are being birthed via induction.

Induction of labour increases the need for pharmacological pain relief (including epidural) which can result in fetal distress from dropping maternal blood pressure, and less available blood supply to baby.

It also increases the need for directed (valsalva) pushing, which also increases the rate of fetal distress. This type of pushing increases reduces cardiac output, lowers arterial blood pressure, reduces blood available to the placenta and therefore to the baby.

The evidence tells us that expectant management (waiting and watching) of growth restricted babies who show signs of being clinically well, versus induced early delivery resulted in no difference in outcomes and reduced the need for obstetric intervention.

In cases of pathological and non-reassuring signs of fetal wellbeing in babies who are truly growth restricted - caesarean section may be safer than the risks associated with induction of labour.

After delivery, FGR babies are more likely to require resuscitation, and standard clinical management is to clamp an cut the cord prior to this. However, compromised babies benefit greatly from remaining attached to their placentas until the blood transfer from the placenta to the baby has completed. Delayed cord clamping or milking the cord before cutting transfers 30% more blood volume to the baby, resulting in higher iron stores, stabilised cardiovascular systems, less need for transfusions, reduces inflammatory responses, prevents permanent damage from hypoxia and protects against neonatal haemorrhage.

Small babies of all kinds are at higher risk of developing low blood sugar levels, and low body temperatures. After birth, the optimal environment for transition to life outside the uterus, when a life-threatening emergency is not imminent is skin-to-skin contact with the mother.

Skin to skin regulates heart rates, respiration, temperature and provides easy access for the establishment of early breastfeeding which directly prevents hypothermia and hypoglycaemia while establishing milk supply for the frequent feeding required to combat physiological jaundice in newborns.

As always, women should be given full understanding of risks, benefits, alternatives - and ultimately make the choice they feel is right for them and their babies.

In the case of small or growth restricted babies - it is very important to distinguish the two - and failing to do so could cause more harm than good.

References
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