Validity of self-reported smoking habits in pregnancy : a saliva cotinine analysis

Background. We examined the validity of self-reported cigarette smoking during the third trimester of pregnancy using saliva cotinine as a marker. Methods. Eligible for the study were 109 pregnant women attending the outpatient Prenatal Service of the Luigi Mangiagalli Clinic (the lar est maternity clinic in Milan) for routine prenatal visits during the third trimester of pregnancy on twenty days in 1994. Women self-reporting current smoking or quitting smoking in pregnancy were asked to provide a saliva sample. Cotinine concentration was analyzed and classified as follows: cotinine not detectable, not probable nicotine use or passive exposure; cotinine <10 ng/ml, not probable nicotine use/probable passive exposure; cotinine, greater than or equal to 10 ng/m, probable occasional or regular nicotine use. Results. A total of 57 (52.3%) women were non-smokers at conception and were excluded from any subsequent analysis. Of the remaining 52 women, 25 self-reported quitting smoking in pregnancy and 27 were current smokers. Saliva cotinine levels were below 10 in 20 of the 25 subjects reporting quitting smoking in pregnancy. The five cases with cotinine greater than or equal to 10 reported a husband smoking more than 10 cigarettes per day. Among the 26 current smokers, seven had a cotinine level <10 ng/ml (four reported smoking fewer then five cigarettes per day and two reported smoking five or more per day); in 20 cases the cotinine value was greater than or equal to 10 ng/ml. Conclusions. These findings provide evidence of a satisfactory validity of self-reported smoking habits in pregnancy