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| C1 Our Trust is worried that introduction of customised charts will put an excessive load on scan resources |
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GROW charts used by properly trained staff do not increase scan requirements in low risk pregnancies. (see B10) and will in fact reduce unnecessary scans if routine one-off scans are replaced by serial fundal height assessment. Increased demand on ultrasound resources is usually a result of raised awareness of the need for serial scanning in pregnancies at increased risk, as recommended by GAP Guidance. The additional demand depends on unit policies. Approximately 25-30% of pregnancies have an increased risk of SGA and stillbirth based on early pregnancy assessment, and case reviews have shown that lack of appropriate surveillance in high risk pregnancies is frequently associated with avoidable deaths. |
| C2 How should fetal growth be assessed in a mother who has had a previous small for gestational age baby? |
| This mother is at increased risk of having another SGA baby; she requires serial ultrasound assessment (3 weekly until delivery) as per the GAP Guidance. |
| C3 Our ultrasound department does not accept referrals for scans at term because they say it is not accurate - what shall I do? |
| Scans for EFW after 37 weeks are at least as accurate as before 37 weeks, with over 70% being within +/- 10%. – see Francis et al, ADC-FNN 2011 |
| C4 How does engagement of the fetal head affect calculation of the EFW? |
| If head circumference cannot be measured accurately because it is too deep in the pelvis, an accurate EFW can also be calculated by a formula which uses abdominal circumference and femur length alone (e.g. Hadlock 2). |
| C5 Should we still be using individual biometry ultrasound charts for assessing fetal growth? |
| Individual parameters should be recorded but plotting them on charts held by mothers can be confusing as we do not have individually customisable charts for HC, AC, FL etc, and population based ‘one size fits all’ charts do not reflect actual growth in a multicultural population. In contrast EFW charts can be adjusted according to individual pregnancy characteristics. |
| C6 If the EFW is below the 10th centile but the population based individual biometry is within normal ranges, what should we do? |
| Customised EFW is more accurate and is better able to distinguish between normal and pathological growth. Individual parameters cannot be customised (see C5). |
| C7 I am a community midwife, if I identify a growth problem with a woman I cannot refer directly for scan, but have to refer to a consultant clinic for review. Sometimes the woman will be referred back to me without a scan, sometimes she will be scanned but I feel the delay in getting the scan is unacceptable. What can I do? |
| Discuss this with your manager. If a clinician with the appropriate training makes a referral because of concerns about the fundal height measurement, we recommend that the measurement should not be repeated and the mother be referred directly and expeditiously for an ultrasound scan to assess fetal growth. |
| C8 My Trust can only afford to carry out one scan at 34 weeks for obese women. How should I monitor growth for the rest of the pregnancy? |
| Mothers with a BMI>35 should receive serial (at least 3 weekly) third trimester scans until delivery, as recommended by the RCOG Green Top guidelines. Fundal height measurements are unreliable in mothers with an increased BMI. |
| C9 How is growth velocity assessed in GROW 2.0? |
Assessment of fetal growth velocity (slow or accelerated) is an important, additional parameter for the assessment of fetal size (SGA or LGA). Previously, growth velocity has been assessed by change in centiles (e.g. 30 centile or 50 centile drop). However centiles, being non-parametric, are unreliable at the extremes of the weight distribution, and the evidence for these methods in terms of ability to identify non-SGA fetuses as being additionally at risk is sparse or non-existent. GROW 2.0 uses a novel method (https://doi.org/10.1002/uog.24860) to assess growth velocity which does not rely in a drop in centiles but on percentage weight loss. Slow and accelerated growth cut-offs are furthermore calibrated according to the interval between measurements, thereby adjusting for potential error of scan estimation of fetal weight. Therefore the limits of normal growth velocity vary with each pregnancy and set of measurements and need to be calculated by computer software. This can be done within the GROW 2.0 app, or with stand-alone calculators for individual or cohorts of measurements, available here: https://www.perinatal.org.uk/growthrate The method (‘Projected Optimal Weight Range’, POWR) has since been validated against pregnancy outcome in two different datasets:
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| C10 Is there any evidence regarding routine third trimester scan to detect SGA or FGR? |
| Antenatal detection of late onset fetal growth restriction remains a challenge. But a routine 3rd trimester scan, usually done at 32 or 36 weeks, is unlikely to detect SGA at birth, as most fetal growth restriction (FGR) is late onset, so may not manifest at the time of such scans.Therefore, a routine scan in the third trimester is ineffective due to poor detection rate, and potentially also dangerous due to false reassurance.
The Cochrane Review states unequivocally that ‘There is no evidence that routine ultrasound in late pregnancy improves perinatal outcomes’ One-off scans are a spot check only, and an inefficient use of resources in light of the chronic ultrasound shortages in the NHS. They cannot provide information on growth trajectory. It is better to perform serial fundal height assessment in low risk pregnancy and refer for scan on indications. The focus should be to ensure that we have sufficient resources so that mothers assessed as having increased risk of FGR get serial scans, as recommended by GAP Guidance. |
| C11 How do customised centiles perform in the identification of macrosomia? |
Macrosomia represents a risk for shoulder dystocia and adverse outcome for baby and mother. Various ways have been used to define macrosomia over the years, including >4kg, >4.5 kg, or > 90th or 95th population based centile. We recommend using >90th customised GROW centile, based on recent studies that have shown that customised centiles improve the identification of macrosomia that is associated with pathological outcome:
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