Associations of maternal age and body mass index with birth weight: a generalized additive model

Abstract

Background: Abnormal birth weight is a major factor in infant mortality, birth defects, and increased risk of various adult diseases. Epidemiological studies on how maternal age and body mass index affect newborn birth weight are still limited. Our study aimed to   explore these relationships to better understand their impact on birth weight.

Methods: A community-based cross-sectional study was conducted using data from the Ethiopian Demographic and Health Survey 2019.  The study included a total of 2,110 participants. Data were collected using a multistage sampling technique to select the study  participants. Inclusion criteria required complete and valid data on maternal age, maternal body mass index, and newborn birth weight.  Linear regression and generalized additive models were employed for the analysis. A pvalue < 0.05 was considered statistically significant.  All statistical analyses were conducted using SPSS and R software.

Results: The average birth weight, low birth weight, and macrosomia were 3,280 g, 1,920 g, and 4,880 g, respectively. In the adjusted  models, a one-year increase in maternal age was associated with a 6.375 g increase in newborn birth weight. Maternal body mass index  was positively associated with birth weight (β=0.323, P < 0.001) and negatively associated with macrosomia (β=-0.041, P < 0.05). The  generalized additive model also revealed an approximately linear relationship between maternal age and body mass index, as well as  between maternal age and birth weight.

Conclusion: These findings confirm that maternal age and body mass index are positively and linearly related to newborn birth weight.  Additionally, maternal body mass index directly influences the likelihood of macrosomia. This study recommends closely monitoring  maternal age and BMI during pregnancy to reduce adverse outcomes and improve maternal health.