Background
Most studies have shown that maternal age was associated with birth weight. However, specific relationships between each additional year of maternal age and birth weight remain unclear. The study aimed to analyze the specific association between maternal age at birth and birth weight.
Methods
Raw data for all live births from 2015 to 2018 was obtained from the Medical Birth Registry of Xi’an, China. 490143 mother-child pairs with full-term singleton live birth and the maternal age ranged from 20 to 40 years old were included in our study. Birth weight, gestational age, the birth date of the newborns, maternal birth date, residence, and ethnicity were collected. Generalized additive model and two-piece wise linear regression model were used to analyze the specific relationship between maternal age and birth weight, risk of low birth weight, and risk of macrosomia.
Results
The relationships between maternal age and birth weight, risk of low birth weight, and risk of macrosomia were nonlinear. Birth weight increased 16.204 g per year before age 24(95%CI: 14.323, 18.086), and increased 12.051g per year when maternal age ranged from 24 to 34(95%CI: 11.609, 12.493), then decreased 0.824g per year (95% CI: -3.112, 1.464). The risk of low birth weight decreased until age 36(OR= 0.917, 95%CI: 0.903, 0.932 for maternal age younger than 27; OR= 0.965, 95%CI: 0.955, 0.976 for maternal age ranged from 27 to 36), then increased (OR= 1.133, 95%CI: 1.026, 1.250). The risk of macrosomia increased with the increase of maternal age (OR=1.102, 95%CI: 1.075, 1.129 for maternal age younger than 24; OR=1.065, 95%CI: 1.060, 1.071 for maternal age ranged from 24 to 33; OR= 1.029, 95%CI: 1.012, 1.046 for maternal age older than 33).
Conclusions
For women of childbearing age (20-40 years old), the threshold maternal age for low birth weight was 36 years old, and the risk of macrosomia increased with the increase of maternal age.