Which growth standard should be used in a preterm obstetric population?

What is it about?

When babies are born preterm, it is more likely that they have experienced growth restriction, which is the failure to have met their growth potential. Growth restricted babies are more likely to experience adverse outcomes at birth, or to be stillborn. However, there are many obstetric growth standards available, and we are still unclear which one best picks up babies that are at high risk of stillbirth or other poor outcomes. Growth charts can be birthweight standards (averaged from all babies born at a particular gestational age), or intrauterine standards (derived from the ultrasound estimated weights of healthy babies growing inside the womb). We compared several birthweight and intrauterine charts to see which was best. We found that the birthweight standards underestimated the amount of babies that should be classified as small. This is likely because they were derived from the cohort of babies born preterm, which inherently had a higher rate of growth restriction. This means that many high risk small babies would be missed. Intrauterine charts picked up an extra group of babies that were high risk of poor outcomes, and are likely a better way of classifying preterm babies as small. Of the intrauterine charts, there was a trade off between sensitivity (how many growth restricted babies were accurately classed as small) and specificity (how many non growth restricted babies were accurately classified as healthy sized), depending on which chart was used.

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Photo by Isaac Quesada on Unsplash

Photo by Isaac Quesada on Unsplash

Why is it important?

If a baby is classified as small during pregnancy, that baby can receive increased monitoring or an earlier delivery in order to reduce the risk of a stillbirth. It is very important that we accurately classify growth restricted babies as small, so that they can receive the interventions needed. It is also important that we don't classify healthy babies accidentally as small, so that they don't receive unnecessary interventions in pregnancy. Our research helps to improve the classification of small babies.