D1 At my Trust we use 2500g as our cut off for postnatal monitoring of growth restricted babies rather than below the 10th centile as we do not want to medicalise care for healthy babies. Is this appropriate?
Since gestational age is now routinely determined at the beginning of each pregnancy, the 2.5 kg cut off is no longer useful, as it mixes up smallness due to immaturity, constitutional factors, and growth restriction. The term ‘small for gestational age’ (SGA) gets around this problem by adjusting the fetal or neonatal size according to the gestational age, with the usual cut-off being the 10 centile, and this limit is further refined by using the customised GROW (gestation related optimal weight) standard.
See RCOG Green Top guidelines
D2 We have implemented GROW and use customised centiles to assess whether the birthweight is SGA. However our neonatologists use the WHO standard to screen for SGA as a risk factor for hypoglycaemia. The two assessments are often out of sync. Which one should we use?
The UK-WHO standard, as used in the parent held Red Book for neonates, is an internationally derived population reference which does not adjust for individual constitutional factors that affect the normal range of birthweight, as recommended by the RCOG. Various studies have shown that a customised standard is better in defining babies at risk of perinatal mortality and morbidity [1-5]. A recently completed comparative analysis with the UK-WHO standard (submitted for publication) has shown that the customised GROW standard identifies a third more cases that are at significantly increased risk of low Apgar scores, admissions to the neonatal unit, and perinatal mortality.
- Clausson B, Gardosi J, Francis A, Cnattingius S: Perinatal outcome in SGA births defined by customised versus population-based birthweight standards BJOG 2001 108:830-4
- McCowan L, Harding J, Stewart A (2005) Customised birthweight centiles predict SGA pregnancies with perinatal morbidity BJOG 2005; 112: 1026-1033
- Figueras F, Figueras J, Meler E, Eixarch E, Coll O, Gratacos E, Gardosi J, Carbonell X: Customised birthweight standards accurately predict perinatal morbidity Arch Dis Child Fetal Neonatal Ed 2007; 92:277-80
- Gardosi J, Francis A. Adverse pregnancy outcome and association with smallness for
gestational age by customised and population based birthweight percentiles. AmJObstetGynecol 2009;201:28.e1-8
- Odibo A, Francis A, Cahill A, Macone G, Crane J, Gardosi J Association between pregnancy complications and small-for-gestational-age birth weight defined by customised fetal growth standards versus a population-based standard J Maternal Fetal Neonatal Med 2011;24:411-7
D3 How do we calculate a customised birth weight centile?
The customised birth weight centile is calculated using any of the GROW software options (GROW-App, GROW-Centile of GROW-API). The date of birth, gender and birth weight of the baby is entered. If your hospital is using the GROW-App or GROW-API it will also ask you some additional questions:
- Unit responsible for providing antenatal care
- Outcome (whether the baby was a live birth or stillbirth)
- Referral for suspected fetal growth restriction, based on fundal height measurement(s)
- Detection of small for gestational age or fetal growth restriction (based on ultrasound scan)
This information is used to provide individual Trusts/hospitals with reports on FGR, referral and detection rates.
D4 We plot the birth weight onto the GROW chart to identify the birthweight centile- is this accurate?
Plotting the birthweight on to the chart will demonstrate a birthweight centile, however this can be calculated more accurately using the GROW web application software. The software also prompts a record whether a referral was made for a scan following a fundal height measurement due to suspicion of fetal growth restriction, and if growth restriction was detected on scan. This information is then used to produce quarterly reports on baseline SGA rates, referral and detection rates, and allows bench marking against the GAP user average.