Conclusions
Using growth standards that rely on a common centile cutoff for every
day of a given gestational week, an infant is significantly more likely
to be considered small if born earlier in the gestational week, and
significantly less likely if born at the end of the week. This leads to
an artefactual distortion of the SGA cohorts, and unequal distribution
of relative risk of stillbirth by days of the week. This anomaly can be
overcome by the use of charts that provide a centile cutoff for each day
of the week, producing uniform SGA classification across the week, and
correcting the distorted risk of stillbirth. We therefore recommend use
of growth standards that give an individual centile cutoff for each day
of the week. If this is not practical, we urge clinicians to be
cognisant of the timing of assessment within the week when making
management decisions.
Acknowledgements
We are grateful to CCOPMM for providing access to the data used for this
project and for the assistance of the staff at Safer Care Victoria. The
conclusions, findings, opinions and views or recommendations expressed
in this paper are strictly those of the author(s). They do not
necessarily reflect those of CCOPMM. NP receives a National Health and
Medical Research Council Postgraduate research scholarship, and a top-up
scholarship from the national Stillbirth Centre of Research Excellence.
AL receives salary support from an NHMRC Ideas grant and ST receives
salary support from an NHMRC Practitioner’s Fellowship. The funding
sources were not involved in the research.