Maternal Age and Low Birth Weight: A Reinterpretation of Their Association Under a Demographic Transition in Southern Brazil

Abstract

To evaluate the relationship between changes in fecundity rates and maternal age and the impact of maternal age on low birth weight (LBW) rates in a developed region in southern Brazil. A time series study evaluating birth weight and maternal ages through the born alive information system (SINASC) in Porto Alegre from 1996 to 2008. The Chi-square test for trends was used to evaluate the trend of LBW and fecundity rates at each maternal age. Population attributed risk (PAR) was used to calculate the impact of maternal age on LBW rates. The study included 271,100 newborns. There was a significant reduction in fecundity rates in all age groups younger than 34 years, but especially in the groups between 20 and 29 years. Overall LBW increased from 9.3 to 10.7 % (P < 0.001). The PAR for LBW showed a reduction in the group from 17 to 19 years (from 1.7 % in 1996-1999 to 0.1 % in 2004-2008), and an increase in the groups from 35 to 39 years (from 2.0 % in 1996-1999 to 2.3 % in 2004-2008) and above 40 (from 1.1 % in 1996-1999 to 1.5 % in 2004-2008). There was a significant change in fecundity pattern in the last 12 years in southern Brazil. Adolescent mothers were surpassed by mothers over 30 years of age in terms of vulnerability for LBW babies. The results show a change in the maternal age distribution towards older mothers, accompanied by an increasing incidence of LBW. This demographic transition also involved a paradoxical pattern with a remarkable reduction in fecundity rates in intermediate maternal age groups with concomitant increase in their risk for LBW.

Cesarean delivery and metabolic risk factors in young adults: a Brazilian birth cohort study

“…CD offspring were also more likely to have greater educational achievement. This finding is in accordance with a study in Brazil, which showed that there has been a change in maternal age distribution toward older mothers accompanied by an increasing low-birth-weight rate (35). Other researchers proposed that the introduction of live saving technologies, such as CD, reaches initially the most-privileged social strata (e.g., high-schooling mothers) (36,37).…”

Pregnancy outcomes in the extremes of reproductive age: A seven-year experience in Tanzania

“…Such a shift in demographic properties of a population in favor of high risk age groups has been observed elsewhere. In Brazil a similar situation in fertility dynamics and in-creasingly delivery at older maternal age above 34 years was observed in one province and had contributed significantly to increased poor pregnancy outcomes such as low birth weight deliveries [26].…”

“…Low birth weight has proved difficult to control among teenagers as proven by the high incidence across countries regardless the level of economical development [13,26,27]. The importance of low socio-economic status of this age group in the causation of low birth weight has been suggested by some studies [1,2] but not by others [3,4].…”

Temporal evolution of the risk factors associated with low birth weight rates in Brazilian capitals (1996-2011)

“…The decrease in the number of adolescent pregnancy in Brazil has been notable in recent years; [ 25 , 41 ] however, high rates are still a concern, mainly in regions of higher socioeconomic vulnerability [ 18 ]. In this study, adolescent mothers are an important factor for LBW, especially in the North, Northeast, and Central West regions, presenting lower socioeconomic development.…”