Shifts in peak month of births and socio-economic factors: a study of divided and reunified Germany 1950–2022

Introduction

Living organisms from plants to animals, including humans, are heavily influenced by their environment. Rhythmic fluctuations in biological processes or behaviour can be observed according to circadian [1] or seasonal changes [2]. Human births also have a strong seasonal pattern which has been consistently demonstrated although the mechanism is not well understood. A role for social factors has been suspected but has not been generally recognized.

Seasonality in human births is a phenomenon that can be traced back a very long time and in practically all populations studied. In the northern hemisphere, this phenomenon has long followed the pattern of a strong seasonal peak in the months of February to April. The phenomenon had been described very early for the German town of Görlitz in the 17th century [3], for a Canadian population in the 17th century [4], it has been reported for Eskimo populations between 1778 and 1918 [5], and the famous statistician Quetelet described it for Brussels in 1826 [6].

European data from the 20th century, but before the introduction of oral contraceptives, for countries such as Sweden, Finland, England, the Netherlands and Germany also show a similar pattern with a marked peak of births in March [7], [8], [9].

There are also a number of studies that report a shift in the peak month of births, which began after the 1970s. This shift has occurred from spring to late summer and has been shown in France [10], Greece [11], Poland [12] and a number of other countries [7]. In Sweden, the disappearance of the spring summit did not result in the formation of a new peak [13].

Most studies point to the introduction of oral contraceptives as an explanation, which has been introduced in practically all countries in which this phenomenon has been studied. However, other socio-demographic and lifestyle factors as well as family planning, which may differ from country to country, have been suggested to influence the shift in peak month of birth.

In this respect, Germany is of interest because between the end of the Second World War and 1990 it was divided by the ‘Iron Curtain’ into West Germany, which belonged politically and economically to the Western bloc, and East Germany, which belonged to the Eastern bloc. While oral contraception was introduced at roughly the same time in both blocs, there were major economic, political and social differences between the two blocs and thus also between the two parts of Germany.

This study aims to investigate the changes in fertility, age of mothers at birth and magnitude of seasonality between East and West Germany from 1950 and 2022. We expand on the study by Lerchl et al. [14] which looked at these factors only in West Germany until 1990. The results will be interpreted against the background of political and socio-economic factors and the availability of oral contraceptives.

Materials and methods

Results

Fertility and mother’s age

In both parts of Germany, there was a considerable increase in births and the birth rate between the mid-1950s and mid-1960s. This was followed by a decline from 1964 in the East and from 1967 in the West, which lasted 10 years in the East and 12 years in the West (Figure 1).

Figure 1:

Number of life births and general fertility rate in East and West Germany from 1950 to 2022. Source: [15].

Until around 1974, there was a sharp decline in the birth rate in both parts of Germany, although this reversed into an increase in the birth rate in the East from 1975 on. This increase continued until 1980 and levelled off slightly until 1987.

A further massive decline to around a third of the maximum birth rate of the 1960s occurred in East Germany in the course of the reunification of the two parts of Germany in 1990 and in the years that followed. However, the decline in fertility in the East recovered over the 20 years following reunification, with the figures in the East even exceeding those in the West in 2017 [18]. Fertility rates are currently falling again in both East and West Germany (Figure 1).

The average age of mothers at birth: In this context, it should be taken into account that in the West, parallel to the decline in fertility and the transition of the month of birth, there was an almost linear increase in the age of women at the birth of their first child from 24.2 to 27.0 years. The increase in the East over the same period was only 23.3 to 24.6 years (Figure 2). It was only when the division of the country was abolished that the birth age of women rose very quickly, reaching the same level as in the West in 2001. In 2022 in both parts of the country the average age increased to more than 30 years.

Figure 2:

Average age of mothers at the birth of their 1st child. Source: [22].

Peak month of births and the magnitude of seasonality

The peak month for births in both parts of Germany from 1950 to 1970 was consistently between March and April – as has also been reported for this period in numerous studies for the northern hemisphere (see introduction above).

In West Germany, there was a continuous shift of the peak month to mid-July in the period from 1971 to 1983, which then stabilised in the month of August from 2005 until the end of the observation period in 2022. In contrast, there was only a slight shift to the end of April in East Germany in the 1970s. It was only after reunification in 1990 that there was also a strong shift to the month of August, which then also remained stable until 2022 (Figure 3).

Figure 3:

Average peak month of births and general fertility rate in East and West Germany from 1950 to 2022. Source: [15].

While the classic annual profile of births is clearly recognisable in both parts of Germany in the 1950–1969 period (+8 %/-8%), the 1970–1989 period shows that the traditional pattern is even more pronounced in Eastern Germany, while in West Germany the deviations tend to be smaller and a shift towards a peak in late summer can already be seen. In the period 1990–2022, the transition to late summer is practically the same in both parts and again very pronounced (+8 %/-8%). Strong seasonality has again been established, albeit with a shift of five to six months (Figure 4).

Figure 4:

Deviation of the monthly number of births from the expected number in three different epochs for East and West Germany (normalised values). Source [15].

Discussion

The decline in fertility after the post-war baby boom began in 1964 in West Germany, but as early as 1962 in East Germany. In this context, it is important to note that oral ovulation inhibitors were available in West Germany from 1961, but only in East Germany from 1965 [19]. Oral ovulation inhibitors are mentioned in the literature as a significant, if not the only factor in explaining the decline in fertility in Western societies [20]. The fact that the decline in the East began earlier than “the pill” was available could be due to political and personal pressure that was increased after 1961 by the erection of the border fortifications, which effectively banned East Germans from travelling to the West [21].

The fertility recovery observed exclusively in East Germany from 1975 onwards can be attributed to a state program specifically designed to boost fertility, offering incentives and material support for starting families and having children [22], 23].

The renewed sharp decline in fertility, which began in 1990 with the political reunification of the two Germanys, was also limited to Eastern Germany. This has been characterised as part of a “demographic shock” in East Germany that also included high out-migration and a temporary decline in male life expectancy in the years following reunification [24]. The fertility decline was interpreted as a response to the sudden increase in economic uncertainties in the East, as well as an opportunity to escape the pressure to have children at a young age [25].

The shift of the peak month of birth from March to August was observed in West Germany as in various other countries at the beginning of the 1970s. It is interesting to note that the change in both parts of the country was associated with a sharp increase in the average age of mothers at the birth of their children, but 20 years later in the East.

The fact that the average age of mothers has increased considerably in the course of the decline of fertility should be seen in the context that women (and their partners) are considerably more likely to have their own home at the time of childbearing than in the past [26]. Together with access to effective fertility control this means that young couples have more freedom and opportunities in choosing the time to conceive a child. The availability of opportunities for sexual activities is relevant for seasonal effects of giving birth is underlined by the fact that Germany as many other countries show an intermediate peak of births around mid-September, indicating that the opportunities provided by Christmas holidays are being seized [27]. The preference for using holidays as favoured times for sexual activities is also evident in analyses of health tracking apps [28].

The comparison of the two parts of Germany indicates that the availability of contraceptives is obviously not the only factor to induce the shift of the peak month of birth. In East Germany, it was only after the political unification of the two parts of Germany – and with the end of the East German state policy towards reproductive behaviour – that there was a simultaneous decline of fertility, an increase in the average age of women of childbearing age, and a shift in the peak month of births. This combination occurred in East Germany only 20 years after it was observed in West Germany, and it could be argued that the freedom to control fertility has only been fully granted after the end of the Eastern state policy towards reproduction.

The freedom to determine their fertility leads to a preference of November as peak month of conception, which in Germany is a month with low outside temperatures and long periods of darkness, where the focus of leisure activities is indoors. Such a constellation, in conjunction with the availability of one’s own apartment, offers sufficient opportunities for activities that lead to reproduction.

In Germany, about half of the women of reproductive age use oral contraceptives [29]. The desire to have children is often associated with the decision to stop taking the pill. If the interval between stopping the pill and conception is on average three months [30], this suggests that the summer holidays are a popular time to stop taking oral contraceptives.

In comparison with other countries, Germany shows a similarly strong pattern after the reunification as before. In other countries (France, Sweden), the transition appears to be less characterised by seasonality and the distribution over the year is more even [10], 13]. The development in Sweden, for instance, is interpreted as more freedom to choose individually and being therefore less dependent on seasonal factors [13]. In this context, a comparative study with Sweden or France would be of interest.