Trends in childbearing and stillbirth risk: Heterogeneity among Italian regions

Abstract In Italy, as in all Western countries, the almost monotonic decline in fertility observed since the 1960s has been paralleled until the beginning of the 1980s by a decrease in maternal age at delivery. Since then, age at marriage and at childbearing has been increasing and marital fertility has continued to decrease. By 1994 Italy showed extreme values of low total fertility rate (1.22) and of high mean maternal age at delivery (29.7). For the period between 1960 and 1994 we identified five U-shaped patterns in maternal age at delivery corresponding to five geographical areas, which differ socioeconomically and culturally. Since it is well known that an increase in the maternal age is accompanied by an increase in the risk of unfavorable pregnancy outcome, we estimated the stillbirth risk run by older (>35 years) mothers who delivered in 1994, with respect to their younger counterparts. The differences between the areas are reflected in the higher risk in southern compared to northern Italy: the maximum value occurred in Sicily (odds ratio 2.02, 95% confidence interval, 1.51-2.70) and the minimum value, even lower than in the north but not statistically significant, was found in Sardinia (odds ratio 1.25, 95% confidence interval, 0.81-1.91), known to be characterized by peculiar cultural and biological features.

KEY WORDS: MATERIAL AGE, CHILDBEARING POSTPONEMENT. REPRODUCTIVE BE

HAVIOR

The diffusion of the Malthusian ideal of birth control and the drastic improvement in living conditions have led all European countries through the demographic transition from moderately high to very low levels of birth and death rates. At the same time, cultural and social processes have been assuming an important role in determining the structure of the populations. Changes in reproductive behavior and reduced fertility in married women, due to the diffusion of voluntary limitation of fertility, represent such processes (Coale 1986; Mason 1997; Pearce et al. 1999; Botting and Dunnell 2000). Postponement of marriage and childbearing by an increasing number of women in Western European countries, Italy included, induced a decline in fertility of women younger than 25 years of age and a continuous rise in fertility of women aged >35 years (United Nations Population Information Network 1999).

In Italy in the first half of the century the transition to voluntary limitation of fertility showed regional heterogeneity in the time of onset and in the diffusion patterns and velocities associated with levels of education and industrialization (Zei and Cavalli-Sforza 1977). Among the factors that might contribute to variations in the timing of starting a family are: the decreasing gradient from north to south still present in economic and educational levels; well-established local traditions, especially in the main islands; interactions between local traditions and women's pursuit of cultural and socioeconomic goals.

The aim of the present paper is to describe the spatial heterogeneity in temporal patterns of maternal age and of the tendency to postpone childbearing in Italy. We also estimated the relative risk of stillbirth in mothers facing a late pregnancy (Lansac 1995; Fretts et al. 1995; Breart 1997; Astolfi et al. 1999; Astolfi and Zonta 2001).

Materials and Methods

National data for the longitudinal analysis were drawn from Italian vital statistics and census publications by Istituto Nazionale di Statistica (Annuario Statistico Italiano 1970-1995; Sommario di Statistiche Storiche dell'Italia 1961-1975). Data for the 15 countries belonging to the European Union (EU15) were drawn from Demographic Statistics 1997, Eurostat.

For the evaluation of the current stillbirth risk, 1994 data for a total of 535,427 individual birth records were obtained from the Italian Istituto Centrale di Statistica at the authors' special request. As for Sardinia, 1993 and 1994 data were pooled because of the relatively small number of births. Only legitimate singleton newborns were considered in order to avoid possible confounding factors.

As defined by the Italian Istituto Centrale di Statistica, total fertility rate is the cumulative age-specific fertility rate computed as liveborns over the population of women aged 15 to 49 years; mean age at delivery refers to the age of mothers of liveborns of any birth order; mean age at first delivery refers to the age of mothers of live firstborns; stillbirths are the fetal deaths occurring in babies of gestational age >=26 weeks; and stillbirth rate is the proportion of stillborns to total newborns.

The relative risk of stillbirth (odds ratio and 95% confidence interval [CI]) were evaluated in older mothers (>=35 years of age) with respect to their younger counterparts (

Maternal education was coded as low, with =8 years of schooling (high school and university diploma).

The temporal trends in maternal age at delivery were analyzed by fitting second order polynomials to the yearly data according to geographical areas, and the minimum of the curves was then evaluated.