Academic journal article Canadian Journal of Public Health

Bias in Maternal Reports of Smoking during Pregnancy Associated with Fetal Distress

Academic journal article Canadian Journal of Public Health

Bias in Maternal Reports of Smoking during Pregnancy Associated with Fetal Distress

Article excerpt


Background. Studies examining the adverse effects of smoking during pregnancy commonly use maternal reports. We hypothesized that if an adverse event occurred during pregnancy, women may underreport smoking. This study looked for bias in maternal report of smoking if fetal distress occurs.

Methods: Data were collected prospectively from patients attending The MotheRisk Program who smoked during pregnancy, and were categorized by delivery outcome, maternal and neonatal characteristics, and the raw number of cigarettes smoked per day during pregnancy reported at clinic and at follow-up. The difference between these two values was compared.

Results: 95 women had uneventful deliveries and 25 had fetal distress. Women who reported fetal distress decreased their report of smoking after delivery compared to their original report during pregnancy, whereas women with an uneventful labour did not (p=0.04).

Conclusions: Our results suggest that if an adverse pregnancy outcome occurs, mothers may tend to underreport their cigarette consumption.


Contexte: Les etudes des effets nefastes du tabac pendant la grossesse emploient commun6ment les declarations des mares. Nous avons suppose qu'en cas de ruction adverse durant la grossesse, les femmes pourraient avoir tendance a minimiser le degre de leur tabagisme. Notre etude visait a detecter un biais dans les declarations, par les meres, de leur utilisation du tabac en cas de detresse foetale.

Methode : Nous avons recueilli des donnees a des fins prospectives aupres de patientes du programme MotheRisk qui fumaient pendant leur grossesse, puis classe ces donnees en fonction du resultat de l'accouchement, des caracteristiques de la mere et du nouveau-ne, ainsi que du nombre de cigarettes fumees par jour pendant la grossesse, selon les declarations des meres a la clinique et lors du suivi. Nous avons ensuite compare les ecarts entre ces deux derniers chiffres.

Risultats : 95 femmes ont signals un accouchement sans probleme, et 25 un accouchement avec detresse foetale. Ces dernieres ont fait etat d'une moindre utilisation de la cigarette apres l'accouchement que durant la grossesse. Pour les femmes ayant accouche sans probleme, le degre de tabagisme declare est reste le meme.

Conclusions : Nos resultats suggerent que lorsqu'une reaction adverse se manifeste a l'issue d'une grossesse, les meres auraient tendance a minimiser leur degre de tabagisme.

Studies examining the potential adverse fetal effects of smoking during pregnancy commonly rely on maternal self-reports. In the event of negative results, researchers often cite underreporting as a potential source of bias.1 This can have a profound effect upon such studies, particularly evident when maternal reports are compared with a biological marker. Studies comparing biochemical markers of smoking, such as serum or urine cotinine levels, with maternal report of smoking found that between 5 and 15% of women who identified themselves as nonsmokers had levels consistent with active smoking.2-4

The use of biological markers, however, is not always feasible for several reasons including reluctance of patients to give consent, which itself can introduce bias, and in the case of retrospective studies where only patient records are available. Moreover, the existing studies,2-4 while identifying a reporting bias of smoking dichotomously (i.e., "yes" versus "no"), were not designed to address a bias in the number of cigarettes reported.

At least two reasons for underreporting have been suggested. First, because of diminishing social acceptance of smoking during pregnancy, mothers may provide false reports of their smoking, believing them to be more socially acceptable to the researchers.5 Second, in the instance of an adverse event during pregnancy or delivery, women may underreport a behaviour that they associate with these adverse events. …

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