Table 2

aRRs for PTB and early PTB according to pre-pregnancy status of FSG and BMI

EventsModel 1*Model 2†Model 3‡
IRR (95% CI)P valueIRR (95% CI)P valueIRR (95% CI)P value
Preterm birth
 Group 1 (n=124,288)6562 (5.28%)1.07 (1.04 to 1.10)<0.0011.06 (1.03 to 1.09)<0.0011.06 (1.03 to 1.09)<0.001
 Group 2 (n=405,190)20 284 (5.01%)1.00 (reference)1.00 (reference)1.00 (reference)
 Group 3 (n=61,389)3107 (5.06%)1.00 (0.97 to 1.04)0.8281.00 (0.97 to 1.04)0.8700.99 (0.95 to 1.03)0.534
 Group 4 (n=12,395)668 (5.39%)1.06 (0.98 to 1.15)0.1101.06 (0.99 to 1.15)0.1081.04 (0.96 to 1.12)0.254
 Group 5 (n=5515)314 (5.69%)1.16 (1.04 to 1.29)0.0081.14 (1.02 to 1.27)0.0161.14 (1.02 to 1.27)0.018
 Group 6 (n=19,824)1035 (5.22%)1.04 (0.98 to 1.11)0.1591.04 (0.98 to 1.10)0.2361.04 (0.98 to 1.10)0.249
 Group 7 (n=4329)241 (5.57%)1.10 (0.97 to 1.24)0.1481.08 (0.96 to 1.23)0.1961.09 (0.96 to 1.23)0.182
 Group 8 (n=1100)83 (7.55%)1.46 (1.18 to 1.79)<0.0011.45 (1.17 to 1.78)<0.0011.45 (1.18 to 1.78)<0.001
Early preterm birth
 Group 1 (n=124,288)1480 (1.19%)1.09 (1.03 to 1.16)0.0041.08 (1.02 to 1.15)0.0081.08 (1.02 to 1.17)0.010
 Group 2 (n=405,190)4488 (1.11%)1.00 (reference)1.00 (reference)1.00 (reference)
 Group 3 (n=61,389)674 (1.10%)0.99 (0.91 to 1.07)0.7650.99 (0.91 to 1.07)0.7350.97 (0.90 to 1.06)0.515
 Group 4 (n=12,395)162 (1.31%)1.17 (1.00 to 1.37)0.0511.17 (1.00 to 1.36)0.0531.15 (0.98 to 1.34)0.080
 Group 5 (n=5515)56 (1.02%)0.94 (0.72 to 1.22)0.6160.92 (0.71 to 1.20)0.5570.92 (0.71 to 1.20)0.539
 Group 6 (n=19,824)209 (1.05%)0.96 (0.83 to 1.10)0.5470.95 (0.83 to 1.09)0.4940.95 (0.83 to 1.09)0.464
 Group 7 (n=4329)40 (0.92%)0.83 (0.61 to 1.13)0.2390.83 (0.61 to 1.13)0.2280.82 (0.60 to 1.12)0.211
 Group 8 (n=1100)14 (1.27%)1.11 (0.66 to 1.87)0.6901.12 (0.66 to 1.89)0.6701.12 (0.66 to 1.88)0.678
  • Pre-pregnancy status of FSG and BMI are defined as follows: group 1, underweight (BMI<18.5) plus normoglycemia (FSG<6.1 mmol/L); group 2, normal weight (18.5–24.0) plus normoglycemia; group 3, overweight (27.9≥BMI≥24) plus normoglycemia; group 4, obesity (BMI≥28) plus normoglycemia; group 5, underweight plus IFG (7.0 mmol/L>FSG≥6.1 mmol/L); group 6, normal weight plus IFG; group 7, overweight plus IFG; group 8, obesity plus IFG.

  • *Model 1: risk ratios were adjusted for sociodemographic characteristics of maternal (age, education level, occupation, ethnicity, region and migrant population) and infants’ sex.

  • †Model 2: risk ratios were additionally adjusted for history of pregnancy (first gestation and primipara) and history of adverse pregnancy outcomes (preterm birth, miscarriage, induced abortion, birth defect and stillbirth).

  • ‡Model 3: risk ratios were adjusted for pre-pregnancy body mass index, active smoking, passive smoking, husband smoking and alcohol consumption status of maternal before pregnancy and active smoking, husband smoking, alcohol drinking status during early stage of pregnancy, in addition to the covariates in model 2.

  • aRR, adjusted risk ratio; BMI, body mass index; FSG, fasting serum glucose; IFG, impaired fasting glucose; IRR, incidence risk ratio; PTB, preterm birth.