FAQs

A1 What’s the use of customised growth charts?
Customised charts predict the growth potential of each baby and display the gestation related optimal weight (GROW) curves. This is done by adjusting for known constitutional / physiological variables (maternal height, weight, ethnic origin and parity), and excluding pathological factors such as smoking and diabetes. As a result, GROW charts are better at identifying pathological growth and confirming when growth is normal than any population based chart. For further information, please see www.gestation.net/literature.htm
A2 What do the lines on the chart signify?
The middle line (50th centile) is the optimal growth curve, which goes through the ‘Term Optimal Weight’ (TOW) point at 40 weeks. The upper and lower lines show the 97th and 3rd centile limits, respectively, for fetal weight. The curves can also be used to plot the slope of fundal height measurements. With any assessment of growth, the slope of serial measurements is more important than individual points.
A3 Do previous birth weights affect the centile lines on the chart?
No, but it is important to input previous baby weights so that the software can display centiles for each baby, to assist risk assessment in the current pregnancy.
A4 Do I need to generate a GROW chart for a woman who books at 30 weeks gestation?
Yes, and the entry of her weight will be an approximation (unless her pre- or early pregnancy weight is known). In any case, late bookers should be considered for serial scans as the accuracy of the gestational age and EDD is likely to be poor.
A5 The electronic system in the GP surgery where I am based shows a population based fundal height chart. Many GPs do not have training in the use of customised charts they are falsely reassured by this information. Help!
It is vital that all clinicians providing antenatal care for women are trained and competent in the use of standardised fundal height measurement and plotting on the mother’s own customised growth chart. One size does not fit all – the chart needs to be adapted to the characteristics of the pregnancy.
A6 Customised charts for Twins
Customised charts are recommended for twin pregnancies and both twins can be electronically plotted in GROW 2.0. Tooltips will show the growth rate and the exact centile each twin is on. The tool tip will also calculate dicordance between the two fetuses.
A7 Ethnicity is often associated with social deprivation. How do you know that it is valid to adjust for ethnic origin?
The GROW method for calculating growth potential considers other factors, including index of multiple deprivation (IMD), and calculates the differences in growth and birth weight which still exist AFTER excluding pathological factors as well as social deprivation [1].
There is other evidence that standards should be adjusted for ethnic variation, from the UK [2], US [3] and Canada [4,5]:
  1. Gardosi J. Ethnic differences in fetal growth. Ultrasound Obstet Gynecol. 1995 Aug;6(2):73-4
  2. Seaton SE, Yadav KD, Field DJ, Khunti K, Manktelow BN. Birthweight centile charts for South Asian infants born in the UK. Neonatology. 2011;100(4):398-403. doi: 10.1159/000325916
  3. Alexander GR, Kogan MD, Himes JH, Mor JM, Goldenberg R. Racial differences in birthweight for gestational age and infant mortality in extremely low risk US populations. Paediatr Perinat Epidemiol 1999;13:205–17.
  4. Kierans W, Joseph K, Luo ZC, Platt R, Wilkins R, Kramer M. Does one size fit all? The case for ethnic-specific standards of fetal growth. BMC Pregnancy Childbirth 2008;8:1.
  5. Hanley GE, Janssen PA. Ethnicity-specific birthweight distributions improve identification of term newborns at risk for short-term morbidity. Am J Obstet Gynecol 013;209(5):428.e1– doi: 10.1016/j.ajog.2013.06.042
A8 Why do I need to enter the mother's booking weight for previous pregnancies?
The birthweight centiles for previous babies is calculated using the booking weight for the relevant pregnancy. This ensures an accurate calculation of birthweight centile for each baby for SGA risk assessment in the current pregnancy. Where possible it is advised to enter the mother's weight at the beginning of each previous pregnancy as it may affect the previous babies' birth weight centiles. If you do not have this information then you can enter the booking weight in the current pregnancy, although this might result in a different centile to what may have been calculated at the end of that pregnancy.
A9 How do we produce a customised chart for a surrogate mother, or when a donor egg is used?
In all circumstances it is the characteristics of the host mother that is used to produce the customised growth chart.