Variation in rates of postterm birth in Europe: reality or artefact?

To compare rates of postterm birth in Europe.

Analysis of data from vital statistics, birth registers, and national birth samples collected for the PERISTAT project.

Thirteen European countries.

All live births or representative samples of births for the year 2000 or most recent year available.

Comparison of national and regional rates of postterm birth. Other indicators (birthweight, deliveries with a non-spontaneous onset and mortality) were used to assess the validity of postterm rates.

The proportion of births at 42 completed weeks of gestation or later.

Postterm rates varied greatly, from 0.4% (Austria, Belgium) to over 7% (Denmark, Sweden) of births. Higher postterm rates were associated with a greater proportion of babies with birthweight 4500 g or more. Fetal and early neonatal mortality rates were higher among postterm births than among births at 40 weeks. Countries with higher proportions of births with a nonspontaneous onset of labour had lower postterm birth rates. The shapes of the gestational-age distributions at term varied. In some countries, there was a sharp cutoff in deliveries at 40 weeks, while elsewhere this occurred at 41 weeks.

These results suggest that practices for managing pregnancies continuing beyond term differ in Europe and raise questions about the health and other impacts in countries with markedly high or low postterm rates. Some variability in these rates may also be due to methods for determining gestational age, which has broader implications for international comparisons of gestational age, including rates of postterm and preterm births and small-for-gestational-age newborns.