Discussion
An increase in clinical intervention by early delivery, including by
labour induction, associated with the SGA GTG guideline and the
introduction of the GROW package was evidenced by the rapid rise in
average monthly induction rate from 21% in January 2015 pre
introduction, to 31.5% in January 2016 and a peak of 36.4% in July
2018. An overall increase of 73% more inductions contemporaneous with
the introduction of GROW. There may have been other components to this
increase but there were no other changes in clinical policies in the
unit.
The purpose of SBL was to reduce stillbirths. The Plymouth singleton
stillbirth rate had fallen between 2010-13, believed to be due to the
introduction of a RCOG Certificate of Completed Training holder
(Consultant or Fellow), resident on delivery suite, including every
night, for 164 hours a week in 2012. The Stillbirth rate did not show a
significant change following the introduction of GROW and the SGA GTG.
Introduction of GROW was also contemporaneously associated with a
massive rise in the number of (post anomaly) growth ultrasound scans.
This put enormous pressure on the obstetric ultrasound service and Fetal
Medicine unit who had to provide 40% scans.
The SGA GTG changed the primary aim of fetal wellbeing screening from
detection of fetal growth restriction (FGR) to detection of SGA fetuses,
despite the guideline identifying that the majority of SGA fetuses will
be normal (constitutionally) small. Concentration on detecting SGA
fetuses would not identify FGR fetuses who were destined to be in the
upper 50 percentiles but were growth restricted to a lower centile,
unless they went below the tenth centile. The majority of FGR fetuses
will not be detected by simply detecting SGA fetuses.
Since moving to IG21, the induction rate rise stopped, and the numbers
of infants allocated as SGA decreased. The question is whether neither
GROW or IG21 are “correct”. The UK90 reference ranges were adopted
across the UK in the late 1990s 8,10 and were
reanalysed in 20093 for inclusion in the UK-WHO growth
charts, still the standards in the Personal Child Health Record (red
book). There are more recent gender specific UK birthweight centiles11 but these have not been adopted nationally. There
is no software package analogous to GROW or IG21, useable on a daily
basis to allocate SGA at birth for either UK90 or others. Of the three
birthweight references tested, the UK90 gave the best true positive and
least false negative rates. It would appear to be the most appropriate
for our routine use.
Screening for fetal wellbeing is a complex process. The primary
screening tools are patient history and SFH measurement. SFH has been in
use for 50 years 11 and there are over 20 uncustomised
SFH references in use 12 but only one
customised.13 If ultrasound is indicated there are
multiple charts for each part of the fetus. In the version of ultrasound
database (Viewpoint 5.6.25.281, GE Healthcare, UK) we are currently
using there are 17 formulae available for calculating estimated fetal
weight (EFW). UPHT policy dictates the Hadlock four parameter
(biparietal diameter, head circumference, abdominal circumference and
femur length) formula 14 which has been published as
the most accurate, although accuracy of EFW is at best ± 10-20%, with a
systematic over estimation.15
The GROW process compiles the errors at each step in the process. If a
fetus is suspected of being small by SFH, with it’s inter and
intraobserver error, an ultrasound is performed. The abdominal
circumference and EFW are calculated, each with their own inter and
intraobserver error dependant on the formulae used. The EFW is then
manually transferred to the GROW SFH/EFW paper chart stored in the
patient’s notes, with manual transcription errors combined with plotting
errors due to the size of the chart. The GROW EFW has its own error
range. At delivery the newborn is weighed and the weight is entered onto
GROW which has another reference range with its errors.
When the change was made to the IG21 process, we introduced IG21 SFH
charts, changed our ultrasound database to use IG21 fetal biometry
references and entered the birthweight into the IG21 software, thus
using references all derived from one dataset 16 in
the hope of reducing accumulated errors. The finding that the IG21
process introduced a significant a skew to the allocation, albeit in the
opposite direction to GROW, was disappointing.
The focus of all the additional work introduced by SBL and SGA GTG was
to reduce avoidable stillbirth. An aim all clinicians support fully.
The review of 200 consecutive
stillbirths, identified that there were similar numbers of stillbirths
who were suspected of being large for gestational age as there were who
were SGA. In addition several stillbirths were ‘expected’, either as a
result of parental choice to interrupt (e.g. delayed selective feticide
giving the survivor twin a better chance at later gestation; feticide at
<24 weeks but delivery occurring after 24 weeks) or where
parental choice was to allow a fetus to die rather than actively end the
pregnancy. With 10-12 stillbirths per year a small number of expected
cases has a significant effect on the total rate, so the process set in
place over the past decade by external guidance, concentrating solely on
detection of SGA rather than fetal health will always have limitations
in reducing avoidable stillbirths.
Screening for SGA is not a Public Health England Screening programme,
unlike screening for trisomies or the anomaly scan. 17
A future larger multicentre study should link neonatal outcome with
antenatal policies to determine which predict poor outcomes, rather than
simply being sizeist.
This study suggests that maternity units should assess the impact on
local intervention rates, clinical outcomes and changes in workload
associated with introduction of programmes like GROW and Intergrowth 21,
but also hints at the need for a centrally organised, properly funded,
PHE specified programme of assessment of fetal growth screening. A
central part of such a programme would be validated birthweight
centiles. As in the trisomy programme 17, sonographers
should be centrally monitored and recertified for biometry measurements.
Standardised ultrasound measurements and EFW formulae using appropriate
longitudinal statistical analysis18,19 should be used
in all units. This approach is already standard for both Crown Rump
Length and Nuchal Translucency measurements and there is a national
quality assurance programme monitoring the process, with local and
national reporting. Surely, if the aim is truly to reduce stillbirth and
perhaps further, to improve all fetal heath monitoring, such a national
Growth screening programme is now required.