In the 1960s caesarean section accounted for approximately 3% of births in many nations of the Western world. By the mid-1980's, however, this rate was beginning to increase and concern was not only being expressed at the rising numbers of babies being delivered abdominally but also at the four-fold difference in national rates, from 5% of births in Czechoslovakia to 18% of births in the United States. This difference, it was argued, could not be explained either by variability in the characteristics of women living in these various countries, nor in their fetuses. The increased use of caesarean section at this time was attributed to a lowering of the threshold at which the operation was being used to manage dystocia (delayed progress in labour), breech presentation, fetal distress and the delivery of small or pre-term infants. The large difference between caesarean rates in North America and some European countries was felt to be due to differences in the management of dystocia and of women who had previous caesarean deliveries.