Table 1

Sociodemographic, lifestyle and clinical characteristics of term and preterm deliveries, spontaneous and electives

All women
(N=38 528)*
Term
deliveries
(n=37 167)
PTD
(n=2361)
OR (95% CI)§sPTD
(n=1075)
ePTD
(n=1286)
p Value
Demographic characteristics
 Maternal age
  <35 years old28655(72.5)27 034 (72.7)1621 (68.7)1.0810 (75.3)811 (63.1)<0.001*
  ≥35 years old10873 (27.5)10133 (27.3)740 (31.3)1.2 (1.1 to 1.3)265 (24.7)475 (36.9)
 Nativity
  European33812 812 (86.0)31857 (86.0)2033 (86.6)1.0926 (87.1)1107 (86.3)0.583
  Non-European5499 (14.0)5168 (14.0)313 (13.3)1.1 (1.0 to 1.2)137 (12.9)176 (13.7)
 Nationality
  Irish27657(70.3)26003 (70.2)1654 (71.8)1.0 (0.9 to 1.1)735 (69.9)919 (73.4)0.063
  Non-Irish11672 (29.7)11022 (29.8)650 (28.2)1.0317 (30.1)333 (26.6)
 Occupation
  Employed36988 (94.2)32236 (87.2)1903 (82.9)1.0849 (81.2)1054 (84.3)0.058
  Unemployed2295 (5.8)4752 (12.8)392 (17.1)1.4 (1.2 to 1.5)196 (18.8)196 (15.7)
 BMI at first prenatal visit, mean (SD)25.5 (5.5)25.5 (5.0)25.9 (5.4)<0.001*24.0 (22.0–28.0)26.0 (23.0–30.0)<0.001*
Lifestyle characteristics
 Smoking status
  Current smoker5880 (14.9)5390 (14.5)490 (20.8)1.4 (1.3 to 1.6)283 (26.3)207 (16.1)
  Former smoker12612 (31.9)11961 (32.2)651 (27.6)0.8 (0.8 to 0.9)276 (25.7)375 (29.2)<0.001*
  Never smoke21036 (53.2)19816 (53.3)1220 (51.7)1.0516 (48.0)704 (54.7)
 Alcohol consumption
  >10 units/week15 (0.0004)10 (0.03)5 (0.23)1.3 (0.9 to 1.9)4 (0.4)1 (0.1)0.269
  1–10 units/week652 (1.8)623 (1.8)29 (1.4)0.1 (0.04 to 0.3)12 (1.2)17 (1.4)
  No alcohol36447 (98.2)34335 (98.2)2112 (98.4)1.0950 (98.3)1162 (98.5)
 Illicit drugs
  Yes2944 (7.5)2705 (7.3)239 (10.5)1.4 (1.2 to 1.7)140 (13.6)99 (7.9)
  No36456 (92.5)34414 (92.7)2042 (89.5)1.0891 (86.4)1151 (92.1)<0.001*
 Domestic violence
  Yes431 (1.1)393 (1.1)38 (1.7)1.5 (1.1 to 2.2)15 (1.5)23 (1.8)0.515
  No38865 (98.9)36635 (98.9)2230 (98.3)1.01009 (98.5)1221 (98.2)
Clinical characteristics
 Parity
  Nulliparous15699 (39.7)14633 (39.4)1066 (45.2)1.2 (1.1 to 1.3)495 (46.0)571 (44.4)0.430
  Multiparous23829 (60.3)22534 (60.6)1295 (54.8)1.0580 (54.0)715 (55.6)
 Planned pregnancy
  Yes27031 (68.7)25 566 (68.9)1465 (63.8)1.0613 (58.8)852 (68.1)<0.001*
  No12344 (31.3)11514 (31.1)830 (36.2)1.2 (1.1 to 1.3)430 (41.2)400 (31.9)
 Treatment for infertility
  Yes702 (1.8)578 (1.6)124 (5.3)2.8 (2.4 to 3.3)31 (2.9)93 (7.2)<0.001*
  No38826 (98.2)36589 (98.4)2237 (94.7)1.01044 (97.1)1193 (92.8)
 Type of pregnancy
  Singletons38717 (97.9)36765 (98.9)1952 (82.7)1.0942 (87.6)1010 (78.5)<0.001*
  Multiples811 (2.1)402 (1.1)409 (17.3)19.1 (16.5 to 22.1)133 (12.4)276 (21.5)
 Prenatal care attendance
  Regular31530 (98.5)29797 (98.8)1733 (92.8)1.0774 (91.1)959 (94.3)
  No attendance or irregular485 (1.5)351 (1.2)134 (7.2)6.5 (5.3 to 8.0)76 (8.9)58 (5.7)0.009*
 Type of labour
  Spontaneous21172 (53.6)20097 (54.1)1075 (45.5)1.01075 (100.0)
  No labour6612 (16.7)5638 (15.2)974 (41.3)3.2 (2.9 to 3.5)974 (75.7)
  Induction of labour11744 (29.7)11432 (30.8)312 (13.2)0.5 (0.4 to  0.6)312 (24.3)
 Mode of delivery
  Spontaneous vaginal22946 (58.1)21974 (59.1)972 (41.2)1.0750 (69.8)222 (17.3)<0.001*
  Instrumental vaginal6013 (15.2)5874 (15.8)139 (5.9)0.5 (0.4 to 0.6)103 (9.6)36 (2.8)
  Elective caesarean5201 (13.2)4945 (13.3)256 (10.8)1.1 (1.0 to 1.3)0 (0.0)256 (19.9)
  Emergency caesarean5367 (13.6)4373 (11.8)994 (42.1)5.1 (4.6 to 5.6)222 (20.7)772 (60.0)
 GA, median (IQR), weeks
  Extremely preterm (<28 weeks)209 (0.5)39.6 (37–41)35 (33–36)33.1 (19–36)33.3 (23–36)0.202
  Very preterm (28 to <32 weeks)342 (0.2)209 (8.9)122 (11.3)87 (6.8)<0.001*
  Moderate to late preterm1810 (4.3)342 (14.5)130 (12.1)212 (16.5)
  (32 to <37 weeks)1810 (76.7)823 (76.6)987 (76.7)
 Birth weight (g) median (IQR)3411.0 (598.8)3471.1 (481.5)2057.3 (729.0)<0.001*2270.0 (1697.5–2665.0)2020.0 (1485.0–2470.0)<0.001*
 Apgar score
  ≥737159 (94.2)35468 (95.4)1691 (71.1)1.0792 (74.3)899 (69.9)
  <72290 (5.8)1691 (4.6)661 (28.9)8.5 (7.5 to 9.4)274 (25.7)387 (30.1)0.019*
 Congenital anomalies
  Yes298 (0.8)250 (0.7)48 (2.0)2.0 (2.2 to 4.1)17 (1.6)31 (2.4)0.188
  No39230 (99.2)36917 (99.3)2313 (98.0)1.01058 (98.4)1255 (97.6)
  • Data presented as n (%).

  • Χ2 test assessed the relationship between categorical variables.

  • Independent sample t-test compared the means of continuous variables.

  • *May not add to total number due to missing; the analyses excluded 2834 women with post-term pregnancies.

  • Term deliveries were defined as deliveries between 37+0 and 40+6 weeks’ gestation.

  • Preterm deliveries were defined as deliveries before 36+6 weeks’ gestation.

  • § Unadjusted ORs and 95% CIs of PTD, with term deliveries as reference category.

  • BMI, body mass index; ePTD, elective preterm delivery; GA, gestational age at delivery; PTD, preterm delivery; sPTD, spontaneous preterm delivery.