Table 3

Adjusted OR (aOR, 95% CIs) for the association of sPTD and ePTD and maternal body mass index stratified by parity and number of fetuses in the index pregnancy, with normal weight as reference category

Underweight BMI<18.5 kg/m2Overweight BMI 25.0–29.9 kg/m2Mildly obese BMI 30.0–34.9 kg/m2Moderate/severely obese 
BMI>35.0 kg/m2
aOR95% CIaOR95% CIaOR95% CIaOR95% CI
All women*
 All PTD1.4(1.08 to 2.0)1.07(0.9 to 1.2)1.1(0.9 to 1.3)1.3(1.04 to 1.7)
 sPTD1.5(1.04 to 2.3)0.9(0.8 to 1.1)0.9(0.7 to 1.2)1.3(0.9 to 1.9)
 ePTD1.4(0.8 to 2.4)1.1(0.9 to 1.3)1.2(0.9 to 1.4)1.3(1.05 to 1.7)
Nulliparas†
 All PTD1.4(0.9 to 2.1)1.07(0.8 to 1.3)1.4(1.1 to 1.8)1.7(1.2 to 2.4)
 sPTD0.9(0.5 to 1.8)1.06(0.8 to 1.3)1.5(1.08 to 2.3)2.8(1.7 to 4.4)
 ePTD1.8(1.04 to 3.4)1.07(0.8 to 1.3)1.3(0.9 to 1.8)1.2(0.7 to 1.9)
Multiparas†
 All PTD1.6(1.04 to 2.6)1.05(0.9 to 1.2)0.9(0.8 to 1.2)1.3(0.9 to 1.7)
 sPTD2.2(1.3 to 3.8)0.9(0.8 to 1.2)0.8(0.6 to 1.1)0.9(0.6 to 1.5)
 ePTD1.01(0.4 to 2.4)1.1(0.9 to 1.4)1.09(0.8 to1.4)1.4(1.02 to 1.9)
Singleton‡
 All PTD1.5(1.1 to 2.1)1.09(0.9 to 1.2)1.2(1.0 to 1.4)1.5(1.2 to 1.8)
 sPTD1.6(1.0 to 2.4)0.9(0.8 to 1.1)0.9(0.7 to 1.3)1.4(1.01 to 2.1)
 ePTD1.5(0.9 to 2.6)1.1(0.9 to 1.4)1.2(0.9 to 1.5)1.4(1.1 to 1.8)
Multiples‡
 All PTD0.6(0.1 to 2.8)1.03(0.7 to 1.5)0.7(0.4 to 1.3)0.7(0.3 to 1.6)
 sPTD0.8(0.3 to 2.1)0.3(0.09 to 1.2)0.4(0.1 to 1.7)
 ePTD0.9(0.2 to 3.9)0.9(0.6 to 1.5)0.9(0.5 to 1.7)0.6(0.2 to 1.7)
  • *Adjusted for maternal age, nativity, occupation, smoking status, parity, attendance to antenatal care, multiples, congenital anomalies.

  • Adjusted for maternal age, nativity, occupation, smoking status, attendance to antenatal care, multiples.

  • Adjusted for maternal age, nativity, maternal occupation, smoking status, parity and attendance to antenatal care.

  • BMI, body mass index; ePTD, elective preterm delivery; PTD, preterm delivery; sPTD, spontaneous preterm delivery.