RESULTS
In this study, we finally included eligible 12 044 reproductive-age
women with singleton birth. We excluded 5414 women without successful
pregnancy within six months. Women who had a singleton birth were
eligible for this study (N = 13 380). Participants with
history of chronic disease and
stillbirth were excluded, yielding an analytic sample of 12 044 women
(Figure 1).
The median of time from baseline examination to pregnancy was 2.2 months
(interquartile range (IQR):1.07-3.67). The mean maternal age was 29.16
±
4.73 years old, and 17.18 % was aged 30 and over. The mean birthweight
was 3163.12 ± 417.20 g, and the frequency of macrosomia was 1.9%. In
terms of maternal FPG level before pregnancy, 1.8% women were in a
hyperglycemic state. Around 17.5% women had a history of adverse
pregnancy outcomes. Most of the women were Han (99.3%) and college or
higher (77.2%). The percentage of history of passive smoking and parity
over three times were 31.1 and 17.1, respectively.
Table 1 showed the baseline characteristics of study subjects according
to maternal age. Compared with younger mothers, women with advanced age
were more likely to be greater birthweight and higher preconception FPG
levels. And, the frequency of macrosomia and hyperglycemia was
significantly increased among older mothers. Women with advanced age
showed to be higher BMI and college or higher, had more history of
adverse pregnancy outcomes and parity.
In adjusted logistic regression model (Table 2), maternal age and BMI
was associated with hyperglycemia. Women with advanced age significantly
had a higher adjusted OR for hyperglycemia by 1.82 (95% CI, 1.31 to
2.52). Every one unit increased in BMI was associated with a 4%
increase per 1 kg/m2 in the risk of hyperglycemia (OR:
1.04; 95% CI: 1.02 to 1.06).
When maternal age was modeled as a continuous variable and fitted in the
multivariate logistic regression model using cubic restricted splines,
continuously increasing trend was found between maternal age and
macrosomia (Figure 2a, P linear< 0.001). It showed that the age of 30 years were likely to be
reasonable cutoff values for advanced maternal age regarding the
macrosomia. Similarly, an obvious linear association was also observed
for preconception FPG levels in macrosomia (Figure 2b, Plinear < 0.001). Based on this age cutoff
values, in multivariate logistic regression model, women with advanced
age had a significant increase of macrosomia (OR: 1.66; 95% CI: 1.22 to
2.26, Table 3). Similarly, a positive association was found between the
risk of macrosomia and preconception FPG level before pregnancy
(OR : 1.30; 95% CI: 1.14 to 1.47, Table 3).
Finally, we explored the contribution of preconception FPG levels to the
association of advanced maternal age with offspring birthweight by a
causal mediation analysis (Table 4). Overall, the total influence of
maternal age on offspring birthweight (the
β coefficient), which includes independent and mediated
effects, was 4.89 (95% CI: 2.92 to 6.81). The presence of preconception
FPG level mediated significantly 8% (95%CI: 4% to 16%) of the total
influence of advanced maternal age on offspring
birthweight.
Additionally, the mediated effect was increased among women with history
of adverse pregnancy outcomes by mediating 18%.