TABLE 1

Background characteristics of the study population (n=2313) stratified by tobacco exposure during pregnancy

SubjectsTobacco exposure during pregnancy#
NeverSnus onlySmoke/dualp-value
Subjects23132061 (89.1)150 (6.5)102 (4.4)
Fetal sex male1097 (53.0)73 (48.7)50 (48.5)0.37
Gestational age at birth2274
 Weeks39.2±1.739.6±1.738.9±1.70.001
 Days274.7±11.6277.5±11.7272.0±11.80.001
Placenta weight g1740656±135.1679±110.2643±144.90.12
Maternal factors
 Age years231332.6±4.130.9±3.232.0±4.8<0.001
 Pre-pregnancy BMI225223.1±3.622.8±3.523.9±4.70.05
 BMI at 18 weeks227824.8±3.624.8±3.625.8±4.80.016
 Weight pre-pregnancy kg226365.4±11.164.8±11.166.4±13.40.55
 Weight at inclusion kg228870.1±11.170.4±11.471.6±13.50.37
 Gestational weight gain up to 18 weeks kg22594.7±3.25.4±3.55.3±3.80.002
Pregnancy history
 Current in vitro fertilisation2300173 (8.4)4 (2.7)0 (0.0)<0.001
 Miscarriage(s) <12 weeks23000.08
  01531 (74.3)126 (84.0)73 (70.9)
  1371 (18.0)15 (10.0)20 (19.4)
  >1146 (7.1)9 (6.0)10 (9.7)
 Miscarriage(s)/stillbirths 12–23 weeks23000.006
  02006 (97.9)148 (98.7)96 (94.1)
  141 (2.0)2 (1.3)5 (4.9)
  >11 (0.0)0 (0.0)1 (1.0)
 Parity21500.008
  01124 (59.2)107 (71.8)59 (57.8)
  1612 (32.2)36 (24.2)29 (28.4)
  >1163 (8.6)6 (4.0)14 (13.7)
Sociodemographic factors
 Education2141<0.001
  Preliminary school only13 (0.7)1 (0.7)2 (2.0)
  High school only175 (9.3)19 (12.8)25 (24.5)
  Higher education <4 years580 (30.7)60 (40.5)42 (41.2)
  Higher education ≥4 years1122 (59.3)67 (45.3)33 (32.4)
  Other1 (0.1)1 (0.7)0 (0.0)
 Country of origin21500.005
  Norway and Sweden1683 (88.6)144 (96.6)87 (85.3)
  Rest of the world216 (11.4)5 (3.4)15 (14.7)
 Marital status2150<0.001
  Married816 (43.0)39 (26.2)30 (29.4)
  Cohabitants1037 (54.6)107 (71.8)66 (64.7)
  Single30 (1.6)2 (1.3)5 (4.9)
  Divorced/separated1 (0.1)0 (0.0)0 (0.0)
  Other15 (0.8)1 (0.7)1 (1.0)
 Living area21500.026
  City, densely populated716 (37.7)76 (51.0)42 (41.2)
  City, less densely populated732 (38.5)52 (34.9)33 (32.4)
  Suburb311 (16.4)15 (10.1)17 (16.7)
  Countryside, village100 (5.3)5 (3.4)5 (4.9)
  Countryside, outside village40 (2.1)1 (0.7)5 (4.9)
 Household income2150<0.001
  Low18 (0.9)3 (2.0)4 (3.9)
  Middle991 (52.2)87 (58.4)72 (70.6)
  High857 (45.1)57 (38.3)24 (23.5)
  Not reported33 (1.7)2 (1.3)2 (2.0)
Smoking history
 Previous smoking2150300 (14.6)75 (50.0)100 (98.0)<0.001
In utero exposure to cigarette smoke2150<0.001
  No1463 (77.0)87 (58.4)73 (71.6)
  Yes256 (13.5)29 (19.5)21 (20.6)
  Do not know180 (9.5)33 (22.1)8 (7.8)

Data are presented as n, n (%) or mean±sd, unless otherwise stated. BMI: body mass index. #: includes four females who answered “yes” to ever-use of other nicotine products (nicotine replacement therapy or electronic cigarettes); one was a daily user during pregnancy at 18 weeks and three quit when recognising pregnancy.