Abstract
Objectives To identify whether advanced maternal age (AMA), defined as age ≥35 years old, is
independently associated with small for gestational age (SGA).
Study Design This was a retrospective cohort of births from the National Vital Statistics System
in the United States from 2009 to 2013. Women were categorized based on four age groups
at the time of delivery: 20 to 29, 30 to 34, 35 to 39, and ≥40 years old. The primary
outcome of SGA < 10th and SGA < 5th percentiles was compared between the four groups
using both univariable and multivariable analyses to determine whether maternal age
was associated with SGA independent of parity.
Results A total of 17,031,005 births were eligible for analysis, with 2,705,501 births to
AMA women. In multivariable analyses, maternal age of 30 to 34, compared with 20 to
29, was associated with lower rates of SGA < 10th and <5th percentiles (adjusted odds
ratio [aOR] = 0.95; 95% confidence interval [CI]: 0.95–0.96 and aOR = 0.97; 95% CI:
0.96–0.98, respectively). The AMA of 35 to 39, compared with 20 to 29, was associated
with lower rates of SGA < 10th percentile and unchanged rates of SGA < 5th percentile
(aOR = 0.97; 95% CI: 0.96–0.98 and aOR = 1; 95% CI: 0.99–1.01, respectively). In contrast,
AMA of ≥40, compared with age 20 to 29, was associated with higher rates of both SGA < 10th
and <5th percentiles (aOR = 1.06; 95% CI: 1.04–1.07 and aOR = 1.14; 95% CI: 1.12–1.16,
respectively). A significant association was found between maternal age and parity
toward the risk of SGA (p < 0.001). Nulliparous women ≥30 years old but not multiparous women had higher rates
of SGA < 10th and SGA < 5th percentiles compared with nulliparous women in the age
group of 20 to 29. In contrast, both nulliparous and multiparous women age ≥40 years
old had an increased risk for SGA < 5th percentile compared with all women in the
age group of 20 to 29.
Conclusion Nulliparous women aged 30 years and older have higher risk of SGA < 10th and SGA < 5th
percentiles compared with nulliparous women age 20 to 29. In contrast, both nulliparous
and multiparous women age 40 years and older have an increased risk of SGA < 5th percentile
compared with all women in the age group of 20 to 29.
Keywords
advanced maternal age - small for gestational age - parity - paternal age
