Table 1 Characteristics of the neonates included in the present study. Values are mean (SD) or n (%) as appropriate.

Nulliparity	8026 (58.8)
Maternal age	30.3 (5.4)
Body mass index	23.4 (4.3)
Smoking at booking
No smoking	10 640 (77.9)
1–9 cigarettes/day	1773 (13)
10–19 cigarettes/day	912 (6.7)
>19 cigarettes/day	336 (2.5)
Low socioeconomic level*	2683 (19.6)
Ethnic origin
White‐European	10 101 (73.9)
Moroccan	60 (0.4)
South‐East Asian	626 (4.6)
Central African	316 (2.3)
South‐American	2490 (18.2)
Other	68 (0.5)
Gestational age at delivery (days)	278.6 (14.4) median 280
Birthweight	3219 (550)
Neonatal intensive care unit admission	387 (2.8)

*Routine occupations, long‐term unemployment or never worked.