Table 1.

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

Characteristics	No (%)
Total No	302 192 (100)
Maternal age at first birth (years):
<20	17 951 (6)
20-24	83 810 (28)
25-29	122 788 (41)
30-34	64 394 (21)
≥35	13 249 (4)
Maternal education (years):
<11	41 551 (14)
≥11	254 743 (84)
Unknown	5898 (2)
Mother born in Nordic country*	258 868 (86)
Maternal smoking†:
No	170 426 (72)
Yes	16 458 (7)
Not registered	48 914 (21)
Maternal prepregnancy body mass index‡:
15-24.9	25 293 (21)
25.29.9	7,287 (6)
≥30	3,633 (3)
Change in partner§	33 574 (11)
Outcome in 1st pregnancy:
Preterm	17 967 (5.9)
Term	284 225 (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)
Stillbirth	551/284 225 (0.2)
Neonatal death	219/284 225 (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).