Table 1

Characteristics of 302 192 women with two successive singleton pregnancies, Norway 1999-2015

CharacteristicsNo (%)
Total No302 192 (100)
Maternal age at first birth (years):
 <2017 951 (6)
 20-2483 810 (28)
 25-29122 788 (41)
 30-3464 394 (21)
 ≥3513 249 (4)
Maternal education (years):
 <1141 551 (14)
 ≥11254 743 (84)
 Unknown5898 (2)
Mother born in Nordic country*258 868 (86)
Maternal smoking†:
 No170 426 (72)
 Yes16 458 (7)
 Not registered48 914 (21)
Maternal prepregnancy body mass index‡:
 15-24.925 293 (21)
 25.29.97,287 (6)
 ≥303,633 (3)
Change in partner§33 574 (11)
Outcome in 1st pregnancy:
 Preterm17 967 (5.9)
 Term284 225 (94.1)
Outcome among women with term 1st pregnancy (No/No at risk (%)):
 Pre-eclampsia¶11 225/266 380 (4.2)
 Placental abruption¶562/266 380 (0.2)
 Stillbirth551/284 225 (0.2)
 Neonatal death219/284 225 (0.1)
 Small for gestational age (2.5th centile)**6939/284 220 (2.4)
  • * Include Norway, Denmark, Finland, Iceland, and Sweden. Information was missing for 4070 (1%) women.

  • For supplemental analysis including smoking at end of first pregnancy as a covariate, women with smoking not registered (n=48 914/235 798 (21%)) were excluded from analysis. As smoking was first recorded from 1999, these analyses include only women whose first births were from 1999 (n=235 798).

  • For sensitivity analysis on prepregnancy, body mass index data are only available incrementally from maternity units from 2006 to 2015. In this period, data were missing for 83 574/119 787 (70%) women.

  • § 296 659 women had an identified partner in both pregnancies.

  • For analysis, the period is restricted to 1999-2014 (n=266 380), as reflected by the percentage.

  • ** To avoid the possibility of data entry issues, term births with birth weight fewer than three digits (≤999 g) were excluded from the small for gestational age analysis (n=5).