International Comparisons of Fetal and Neonatal Mortality Rates in High- Income Countries: Should Exclusion Thresholds Be Based on Birth Weight or Gestational Age?
Abstract
We compared the effects of using a 1000-gram birth weight or a 28-week gestational age threshold on reported rates of fetal and neonatal mortality in Europe. Methods: Aggregated data from 2004 on births and deaths tabulated by birth weight and gestational age from 29 European countries/regions participating in the Euro-Peristat project were used to compute fetal and neonatal mortality rates using cut-offs of 1000-grams and 28-weeks (2.8 million total births).
We measured differences in rates between and within countries using the Wilcoxon signed rank test and 95% confidence intervals, respectively. Principal Findings: For fetal mortality, rates based on gestational age were significantly higher than those based on birth weight (p, 0.001), although these differences varied between countries.
The use of a 1000-gram threshold included 8823 fetal deaths compared with 9535 using a 28-week threshold (difference of 712). In contrast, the choice of a cut-off made little difference for comparisons of neonatal deaths (difference of 16).
Neonatal mortality rates differed minimally, by under 0.1 per 1000 in most countries (p = 0.370). Country rankings were comparable with both thresholds.
Conclusions: Neonatal mortality rates were not affected by the choice of a threshold. However, the use of a 1000-gram threshold underestimated the health burden of fetal deaths.
This may in part reflect the exclusion of growth restricted fetuses. In high-income countries with a good measure of gestational age, using a 28-week threshold may provide additional valuable information about fetal deaths occurring in the third trimester.