However, shortly afterwards came what would eventually be called the baby boom. This went through its ascending phase during the war years themselves in two European countries - Sweden and Switzerland - that remained outside the conflict. Elsewhere in western Europe, the boom did not become fully apparent until the end of the hostilities, but it then manifested itself with great vigour, even if taken as a whole, in terms of total rates, the increase in fertility between the early 1930s and the late 1950s in a country like France (about +0.8 child per woman) was identical to that observed in Sweden or Switzerland (figure 1, graph at bottom right). In North America the baby boom assumed still larger dimensions than in Europe, the total rates for the United States and Canada reaching, respectively, 3.0 and 3.4 children per woman in 1950, then 3.7 and 3.9 in 1957 (figure 2). On the other hand, in Austria and Germany, where fertility had increased in the late 1930s, there was no rise from 1945 to 1955. In southern Europe, where the demographic transition came later, the baby boom was hardly noticeable, fertility being still high around 1950. During the period 1955-1965, total fertility rates generally showed an upward trend in western Europe and North America, owing partly to lower ages at marriage and, consequently, at maternity; added to the normal annual number of births (i.e. that which would have been observed all things being equal) was the surplus resulting from these lower ages of marriage and childbearing. The lowering of the age at marriage was by then a well-established phenomenon, which had started to become manifest shortly after the First World War; it was to continue until the mid-1970s (and even up to the beginning of the 1980s in southern Europe), with a shift towards earlier family formation. The increasing rarity of higher-order births (four or more) combined with the lowering of the age at marriage had the effect of reducing the average age at maternity.