Table 1

Sociodemographic, pre-existing and pregnancy-related clinical characteristics of women

Cases n=1041Controls n=1984Unadjusted analysis
n%n%OR(95% CI)P value
Maternal age (years)0.30
 Under 20434.1552.81.55(0.98 to 2.46)
 20–2417717.032516.41.08(0.85 to 1.37)
 30–3434232.962831.71.08(0.89 to 1.32)
 35–3915514.932416.30.95(0.74 to 1.22)
 ≥40121.2331.70.72(0.40 to 1.30)
Ethnic group0.004
 White (UK and Ireland)64161.6121061.01
 White (other)17016.324612.41.30(1.05 to 1.62)
 Asian14013.528914.60.91(0.76 to 1.10)
 Black514.91346.80.72(0.50 to 1.03)
 Other393.81055.30.70(0.46 to 1.06)
Socioeconomic status0.06
 Higher managerial, admin, prof30128.954027.21
 Intermediate20219.436218.31.00(0.81 to 1.24)
 Routine and manual23722.849925.20.85(0.69 to 1.06)
 Unemployed/Student1009.61608.11.12(0.88 to 1.43)
 Employed, job unrecorded or uncodable666.31236.20.96(0.70 to 1.33)
 Employment status not recorded13513.030015.10.81(0.65 to 1.00)
Area deprivation quintile*0.29
 First (least deprived)17517.037419.01
 Second19218.639019.91.05(0.82 to 1.35)
 Third21120.540920.81.10(0.87 to 1.40)
 Fourth24223.540820.81.27(0.98 to 1.64)
 Fifth (most deprived)21020.438319.51.17(0.92 to 1.49)
Smoking status0.71
 Non-smoker during pregnancy90386.9172086.71
 Smoker during pregnancy12512.023511.81.01(0.80 to 1.28)
 Not recorded111.1291.50.72(0.32 to 1.61)
Previous pregnancies ≥24 weeks<0.0001
 052350.270435.51.98(1.70 to 2.31)
 213713.228014.11.31(1.03 to 1.65)
 3 or more535.11256.31.13(0.77 to 1.67)
BMI at booking (kg/m2)0.44
 <18.5232.2562.80.73(0.42 to 1.26)
 18.5–24.952950.8106353.60.88(0.75 to 1.05)
 30–35.0898.61547.81.03(0.76 to 1.38)
 >35.0262.5341.71.36(0.78 to 2.37)
 Not recorded787.51517.60.92(0.73 to 1.16)
Pre-existing medical risk factors†0.69
 One or more151.4251.31.14(0.59 to 2.21)
Problems in a previous pregnancy‡ (multiparous women only)0.03
 One or more244.6332.61.83(1.05 to 3.20)
Current pregnancy maternal problem§0.07
 One or more878.41316.61.29(0.98 to 1.71)
Current pregnancy fetal problem¶0.03
 One or more191.8180.92.03(1.06 to 3.88)
Sex of baby<0.0001
 Male63060.8100950.91.50(1.27 to 1.76)
Gestation at birth (weeks)0.20
 36–37373.6502.51.46(0.91 to 2.35)
 3812712.321310.81.18(0.90 to 1.53)
 3929528.562331.50.93(0.78 to 1.12)
 41–4221620.838019.21.12(0.94 to 1.34)
  • *Area deprivation quintiles created using children in low-income families measure.37

  • †Essential hypertension; confirmed cardiac disease; thromboembolic disorder; atypical antibodies; hyperthyroidism; diabetes; renal disease; epilepsy.

  • ‡Unexplained stillbirth/neonatal death or previous death related to intrapartum difficulty; previous baby with neonatal encephalopathy; primary PPH requiring treatment/transfusion; shoulder dystocia; previous caesarean section; other.

  • §GBS; BMI >35 kg/m2; post-term pregnancy; pre-eclampsia/pregnancy-induced hypertension; preterm prelabour rupture of membranes; substance misuse/alcohol; gestational diabetes; other.

  • ¶Malpresentation; small for gestational age; reduced fetal movements; fetal abnormality.

  • BMI, body mass index; GBS, group B streptococcus; PPH, postpartum haemorrhage.