Gestational diabetes mellitus: accuracy of Midwives Data Collection

In reply: Moses et al are correct in noting that gestational diabetes mellitus (GDM) is under-reported to the New South Wales Midwives Data Collection (MDC). The most recent validation study of the MDC was carried out in 1998. We reviewed a random sample of 1680 medical records from NSW public and private hospitals, representing 1.9% of births reported in 1998. The sensitivity and specificity of reporting of GDM to the MDC were 86.7% and 99.6%, respectively.1 In this sample, the incidence rate of GDM was 3.5% according to the MDC, and 4.0% according to the medical record review.

These population rates are lower than the rates reported by Moses et al among women attending hospitals in Wollongong. In addition to incomplete recording of diagnosed GDM on the MDC, the low rate of recording of GDM in medical records in our sample suggests that GDM was also under-ascertained at a population level. This is probably due to variations in the implementation of pregnancy screening for GDM between clinicians and across NSW hospitals.

In February 2003, the Royal Australian and New Zealand College of Obstetricians and Gynaecologists endorsed the Australian Diabetes in Pregnancy Society GDM Management Guidelines.2 The guidelines recommend universal screening for GDM, noting that selective screening may be appropriate because of limited resources or known low GDM incidence.

The suggestions for trying to improve reporting of GDM by redesigning the MDC form are welcome, and we will certainly consider them at the next review. We are also considering using the hospital Inpatient Statistics Collection (ISC), in which discharge diagnoses are classified according to the International Classification of Diseases, as an alternative source of information on maternal morbidity. We are currently reviewing a random sample of 500 medical records of mothers who gave birth in hospitals throughout NSW. The information obtained will be compared with matched ISC records provided to the NSW Department of Health to determine whether the ISC is a more reliable source of information on maternal morbidity than the MDC. In the longer term, I anticipate that the integration of the MDC with computerised medical records in hospitals will also contribute to improved reporting.

Under-reporting of maternal morbidity, including GDM, is an issue for all state and territory perinatal data collections in Australia. The information is used for planning and evaluation of healthcare services, so it is important that we get it right. I would like to thank Moses et al for raising this issue.