RESULTS
Baseline characteristics of the study population were showed inTable 1 . A total of 5,986 mother-newborn pairs were included in
the analyses and 5.7% (n=344) of them were preterm birth. The mean
maternal age at delivery was 32.2±4.7 years and the mean pre-pregnancy
BMI was 20.7 ± 2.9 kg/m2. The median values (IQR) of
ApoB, ApoA-1 and ApoB/ApoA-1 ratio were 2.07 (0.30) g/L, 0.96 (0.28) g/L
and 0.47 (0.14), respectively. The results showed that preterm birth
occurred more frequently in those mothers with more adverse risk
profiles, including being older at delivery, multiparous, had higher
pre-pregnancy BMI, with higher ApoB and ApoB/ApoA-1 levels during second
trimester.
The relationships between maternal apolipoprotein levels and PTB were
presented in Table 2. In the crude model, participants in the
highest tertile of ApoB (OR, 1.54; 95% CI, 1.17-2.02; P for
trend= 0.002) and ApoB/ApoA-1 (OR, 1.42; 95% CI, 1.09-1.85; Pfor trend= 0.007) had a significantly higher risk of PTB, compared to
those in the lowest tertile. Adjustment for potential confounders did
not materially alter the positive associations between ApoB, ApoB/ApoA-1
and PTB. Compared with the lowest
tertiles, individuals in the highest
tertile of ApoB had a 41% higher risk of PTB (OR, 1.41; 95% CI,
1.07-1.87; P for trend= 0.017) and those in the highest tertile
of ApoB/ApoA-1 had a 35% higher risk of PTB (OR, 1.35; 95% CI,
1.03-1.78; P for trend= 0.024). There are no differences in the
risk of PTB across the ApoA-1 tertiles. When continuous variables were
used, each 1-g/L increase in ApoB and each 1 unit increase in
ApoB/ApoA-1 were positively related to the risk of PTB (OR, 2.33; 95%
CI 1.40-3.86 for ApoB and OR, 4.10; 95% CI, 1.47-11.36 for
ApoB/ApoA-1). We further conducted restricted cubic spline to estimate
the dose-response relationships between apolipoprotein levels and PTB
(Fig. 2 ). The results indicated that ApoB (P for
non-linearity= 0.943) and ApoB/ApoA-1 (P for non-linearity=
0.284) were both linearly associated with the risk of PTB, whereas
ApoA-1 was not associated with PTB (P for all = 0.092).
The results of subgroup analyses were shown in Table 3 . Even
though there was no interaction between all of the stratification
variables and preterm birth (all P for interaction >
0.05), the positive relationship between maternal ApoB/ApoA-1 and
preterm birth was stronger in women with pre-pregnancy BMI ≤ 24
kg/m2, age at delivery ≥ 35 years or those who were
multiparous. In the sensitivity analyses, the positive relationships
between ApoB, ApoB/ApoA-1 ratio during pregnancy and preterm birth were
not materially changed after excluding pregnant women with GDM
(Table 4 ).