This cost analysis was based on data from a cluster-randomised GDM prevention trial (N = 848), conducted at maternity clinics in Finland in the period from 2007 to 2009. During pregnant women’s routine visits to the maternity clinic, public health nurses recruited all women up to 12 weeks pregnant. The inclusion criteria of the original study were: BMI ≥ 25 kg/m², previous occurrence of GDM, or any signs of glucose intolerance, a macrosomic newborn (≥ 4500 g) in any earlier pregnancy, type 1 or 2 diabetes in first- or second-degree relatives or age ≥ 40 years. Women included in the trial were either primigravida or multigravida with singleton pregnancies. The exclusion criteria were: pathological value in baseline oral glucose tolerance test (OGTT) at 8–12 weeks’ gestation (blood glucose > 5.3 mmol/l at fasting, > 10.0 mmol/l at 1-hour or >8.6 mmol/l at 2-hour), type 1 or 2 diabetes before pregnancy, inadequate Finnish language proficiency, age < 18 years, twin pregnancy or physical limitation preventing physical activity.
In the present study, the case definition of GDM included women with a pathologic oral glucose tolerance test or ongoing insulin treatment. Women exhibiting no GDM diagnostic criteria formed a comparison group. The cost comparison included health care costs accruing to the municipality of residence and to the patient. The costs were evaluated from a societal perspective, including costs to the patient. This is because, in the tax-based health care system in Finland, the patients’ municipality of residence reimburses the real health care costs to the relevant hospital district. However, the daily charges for outpatient- and inpatient care also create a small cost to the patient. The cost analysis included all eligible women from the GDM prevention trial who had signed a study-participant consent form and had given us their permission to use their data in the Medical Birth Register and the Care Registers for Social Welfare and Health Care. Because the travel expenses and time costs related to the use of health services were assumed to be minor, they were not included in the calculation.
Costs were taken into account from the beginning of the pregnancy until the last day that the mother and her newborn spent in hospital after the birth. Information concerning medication and the number of visits to primary and secondary care was obtained from maternity cards filled in by the public health nurse at the maternity clinic. Information on visits to a diabetes nurse or a dietician was collected from questionnaires filled in by the mothers at the beginning of the study (at 8–13 gestational weeks) and again at 26–28 and at 37–39 gestational weeks. The information on the number of the mother’s inpatient hospital days before and after the standard delivery stay, the mode of delivery, the ICD-10 diagnosis code of the mother and newborn and the number of hospital days of the newborn were obtained from the Medical Birth Register and the Care Register.
Primary health care costs were based on the average national unit costs for health care, which includes visits to the public health nurse and to the doctor . The costs of visits to secondary care, visits to a diabetes nurse and a dietician, the modes of delivery, inpatient days and neonatal intensive care units use were estimated by using the unit costs of the Tampere University Hospital, which was the hospital in which 93% of the deliveries took place and is the second largest hospital in Finland . The unit costs were entered at the price level for 2009. Unit costs of obstetric outpatient and inpatient care included salary costs and administrative expenses, laboratory expenses as well as costs for all professionals participating in the provision of health care.
The cost evaluation included only inpatient days preceding and following delivery in hospital units related to pregnancy and GDM. The standard inpatient daily charge of 30 Euros was added to the unit cost, which was the cost to be paid by the patient. In the cost analysis, pre-delivery inpatient days were counted until the delivery and during the immediate post-partum period after delivery using the average national inpatient day cost . Delivery cost and inpatient day costs due to delivery were counted separately using the Tampere University Hospital unit cost , which was used to obtain detailed DRG (Diagnosis Related Groups) information. Delivery unit costs included a standard number of inpatient days, depending on the mode of delivery. In addition, delivery-related operation costs included the salary costs of obstetric staff, including administrative expenses, medication and the cost of neonatal care in cases without an ICD-diagnosis. The newborn babies’ hospital stays were calculated separately in cases when the newborn needed care in a neonatal intensive care unit because of a disease involving organic complications or another ICD-10 diagnosis.
If the newborn had an ICD-10 diagnosis code, the costs of the newborn’s care were evaluated using the classification of the delivery hospital, where the costs of newborn babies were allocated to one of three possible unit cost categories, depending on the newborns’ birthweight, ICD-10 diagnosis code and the number of inpatient days in hospital. In the case of rooming-in, the costs of the newborn baby’s care were included in the mother’s delivery unit cost.
Medication costs included insulin costs but not the costs of glucose monitoring at home, as these were known to be minor . Insulin costs were calculated for a period of 2.5 months and included health insurance reimbursements. According to the Finnish national guidelines, insulin treatment should be started, if necessary, at the 30th gestational week and should continue until delivery . The costs of the oral glucose tolerance test (OGTT) as a diagnostic test for GDM were assumed to have been incurred once in both groups. In the original study, a pathologic OGTT result at 8–12 weeks’ gestation was a criterion for exclusion from the study, which meant that a large amount of information concerning the costs of OGTT was missed (N = 174).
The association between the groups and continuous variables was tested with the Mann–Whitney U-test and with the chi-square test for categorical variables. Costs were reported as means and were rounded to whole Euros. Mann–Whitney U-test was used to analyse the differences between the two groups. Ratios or proportions of prenatal complications and mode of delivery variables were calculated using the chi-square test or, if the assumptions of the chi-square tests were not valid, Fisher's exact test. Total costs were adjusted for maternal age, body mass index and education. These adjustments were performed using ordinal regression analysis, because cost distributions were not normally distributed. The results were considered to be statistically significant if p < 0.05. All analyses were performed using SPSS software (version 19).