The Effect of Maternal Age at the First Childbirth on Gestational Age and Birth Weight: The Japan Environment and Children's Study (JECS).

BACKGROUND

In Japan, mean maternal age at first childbirth is increasing. The aim of this study was to investigate whether maternal age at the first childbirth is a risk factor for preterm birth (PTB), low birth weight (LBW), and small for gestational age (SGA).

METHODS

We used the results of Japan Environment and Children's Study (JECS) who gave birth in 2011-2014. Cases of primiparous singleton pregnancies where the subject was ≥20 years and delivered after 22 weeks were included. All subjects were categorized into five groups according to maternal age: 20-24, 25-29, 30-34, 35-39, and ≥40 years. Adjusted odds ratios (aORs) for PTB (before 37 and 34 weeks), LBW (<2,500 g and <1,500 g), and SGA were calculated using a logistic regression model, with the 20-24-year age group as reference.

RESULTS

We analyzed 38,412 singleton primiparous pregnancies. The aORs of all outcomes increased in parallel with each maternal age group >30 years. The aORs of PTB before 37 and 34 weeks, LBW <2,500 g, LBW <1,500 g, and SGA in the 30-34-year age group were 1.39 (95% confidence interval [CI], 1.16-1.67), 2.23 (95% CI, 1.45-3.41), 1.34 (95% CI, 1.18-1.53), 2.30 (95% CI, 1.35-3.94), and 1.24 (95% CI, 1.05-1.46), respectively.

CONCLUSION

The present study showed that higher maternal age (>30 years) at the first childbirth was an independent risk factor for PTB, LBW, and SGA.