The following examples illustrate some of the issues which have arisen during discussion and training sessions, specifically relating to normal, static, slow and excessive growth.

Example 1 - Normal Growth

Normal variability in measurement means that the slope will alter from one measurement to another. The line may cross centiles, but the overall slope of the curve should not be static (no growth over 2-3 weeks) and becomes abnormal if the slope falls away in subsequent measurements. In the case of normal fundal height growth, the measurements should reflect the curve on the customised charts. Using these charts in very small and very large women should reduce the number who will be referred for ultrasound assessment.

Example 2 – Static Growth

In this example, the measurement is identical in two measurements separated by 2 weeks. We would consider this to be an abnormal pattern, and should prompt referral for ultrasound assessment. Static growth has the same significance whether the original measurement is above the 90th Centile, on the 50th, or on the 10th Centile. The potential impaction is static fetal growth, and possibly also reduced liquor volume, both of which are associated with intrauterine death.

Example 3 – Slow Growth

It might be difficult to determine when then growth of the fundal height is slow. The essential feature is that you are concerned about it, and it is likely that the pattern will have emerged over 3 or 4 measurements. We are not able to define the referral criteria, but growth curves which cross centiles from higher to lower are of concern. It is absolutely vital that you plot your fundal height measurements correctly with a cross, so that the radiographer or midwife undertaking the ultrasound assessment can see clearly why you have referred the case. If the EFW is similarly clearly plotted (with an open circle) you will have the ultrasound assessment of fetal weight, put into context by the customised chart.

Example 4 – Excessive Growth

The clinical concerns about large for dates are very much less than small for dates. A large for dates pregnancy might be first presentation of gestational diabetes, which can present with both a large baby and polyhydramnios. The ultrasound assessment will address the issue of fetal size and polyhydramnios, and should prompt a re-evaluation of the fetus for structural anomalies. Large babies can be very difficult to predict using Ultrasound, and it is even more difficult to know whether to recommend elective caesarean sections in these cases. The evidence to date is that the diagnosis of macrosomia in the fetus is of doubtful benefit in terms of improving the outcome, once of the issues of diabetes have been resolved.

The fundal height measurement is known to have considerable variability, often being above the 90th Centile on the customised charts in the 24 – 30 week range. We therefore recommend that an initial measurement above the 90th Centile does not prompt ultrasound referral, but is repeated and is only assessed by ultrasound examination if the plot increases steeply (which might occur with polyhydramnios). The emphasis here is again on using your clinical judgement, if the circumstances are those where there is a high risk of gestational diabetes, the expectant mother will be offered screening for diabetes with a random blood sugar or GTT.

Cases showing a large fundal height will contain some interesting cases with rare complications of pregnancy, but we must remember that the initial observations at 24- 28 weeks are very frequently above the 90th Centile, because the customised charts have been produced with the estimated fetal weight primarily in line.

Good communication is essential, and one message, which can be quite frightening to a mother, is that she is having a big baby. It is therefore appropriate to reassure the mother and repeat the fundal height measurement 2 to 3 weeks later. Ultrasound is notoriously poor at predicting the weight of big babies, a calming reassuring approach is very important.