Original Article www.jpgmonline.com Effects of passive smoking on outcome in pregnancy Goel P, Radotra A, Singh I, Aggarwal A, Dua D Department of Obstetrics ABSTRACT and Gynaecology, Background: Adverse health effects of exposure to environmental tobacco smoke (ETS) among non-smokers Government Medical College and Hospital, have been studied occasionally in developing countries. Chandigarh - 160029, Aims: To study the effects of exposure to ETS on outcome in pregnancy India. Settings and Design: A cross-sectional study at a secondary level teaching hospital Material and Methods: Consecutive 576 non-smoking women delivering a singleton live baby were studied. A Correspondence: pre-designed structured questionnaire was used to record the details of exposure to ETS at home. The maternal Poonam Goel, MD E-mail: [email protected] and foetal variables were compared among those who were exposed to ETS vis-à-vis not exposed. Unpaired Student t-test was used for the comparison of continuous variables and Fisher’s Exact test was used for categorical variables. Multiple logistic regression analysis was performed after including all variables found to have significant differences on univariate analysis. Results: Of the 576 women studied 141 (24%) were exposed to ETS. In the mothers exposed to ETS, there was a significantly higher incidence of pre-term birth (24.1% vs. 16.1%; P = 0.027) and small-for-gestation babies (31.9% vs.17.2%; P<0.001) as compared to unexposed mothers. The mean birth weight of the babies born to the mothers exposed to ETS was 138 g less than that of babies in the unexposed group (2632 +577 g vs. 2770 +562 g respectively, P = 0.014). The multiple logistic regression analyses showed that ETS exposure during pregnancy was significantly associated with a higher risk of small-for-gestation babies (OR 2.10; 95% CI: 1.27- 3.48). Received : 21-10-03 Conclusion: Exposure to ETS during pregnancy is associated with higher risk of having a small-for-gestation Review completed : 20-11-03 baby. Accepted : 06-01-04 PubMed ID : 15047992 KEY WORDS: Passive smoking, environmental tobacco smoke, pregnancy, outcome, small-for-gestation J Postgrad Med 2004;50:12-16 xposure to environmental tobacco smoke (ETS) has been underlying mechanisms for these effects are yet to be eluci- E variously described as passive smoking, ‘second-hand dated. It is possible that the carbon monoxide in the smoke smoke’ or involuntary smoking and is recognised as a major could be combining with haemoglobin, in turn, leading to foetal health hazard. 1, 2 The International Consultation on Environ- hypoxia. In addition, nicotine in the smoke could be causing mental Tobacco Smoke (ETS) and Child Health concluded vasoconstriction further aggravating foetal hypoxia. It has also that maternal smoking during pregnancy is a major cause of been proposed that nicotinic effects may be due to the conse- reduced birth weight, decreased lung function and sudden in- quences of inappropriate stimulation of nicotine cholinergic fant death syndrome (SIDS).3 Exposure to ETS among non- receptors and its neuroteratogenicity.10 smoking pregnant women can cause a decrease in birth weight. Most of the evidence for these conclusions was drawn from The association of ETS with adverse foetal and reproductive studies conducted in the Western and developed countries. A outcomes has been the subject of two recent publications.11,12 study from Nagpur, India found maternal ‘tobacco exposure’ Smoking is on the rise in developing countries.13 Environmen- to be significantly associated with low birth weight in babies. 4 tal conditions like overcrowding may make the health effects of ETS more pronounced. The adverse health effects of pas- ETS is a combination of side-stream smoke that is emitted sive smoking have been studied in developing and underde- from the burning end of a cigarette and the mainstream smoke veloped countries only occasionally. Most of the studies from exhaled by the smoker. Side-stream smoke constitutes about India are on the pulmonary effects of passive smoking.14 In this 85% of the smoke present in the room and contains many po- study we examined the effects of exposure to ETS on the ma- tentially toxic gases in higher concentrations than in the main- ternal and foetal outcome in pregnancy. stream smoke.5 ETS has been classified as a class A (known human) carcinogen along with asbestos, arsenic, benzene and Material and Methods radon gas.6 Active smoking is a well-established cause of intra uterine growth retardation (IUGR) among humans. 7-9 The The study was conducted at a large secondary care teaching hospital 12 J Postgrad Med March 2004 Vol 50 Issue 1 12 CMYK Goel et al: Passive smoking in pregnancy in North Western India. The study group comprised 576 consecutive er’s Exact test was used for the comparison of categorical variables. non-smoking women delivering a singleton live baby. Following the Multiple logistic regression analysis was performed after including delivery, each woman was interviewed according to a pre-designed all co-variables found to have significant differences on univariate structured questionnaire to enquire if they had been exposed to ETS analysis for categorical outcome variables. For continuous outcome at home. The questionnaire recorded details of the average daily ex- variables multiple linear regression modelling was done on similar posure, besides enquiring into their knowledge and perceptions about lines. passive smoking. Obstetric and medical details of the mothers were noted from hospital records, as were the details of the baby. Results Based on the history of exposure to ETS the study population was Of the 576 women studied 435 (75.6%) did not have any ex- divided into two groups. The maternal and foetal variables were com- pared in the subjects exposed to ETS with those who were not ex- posure to tobacco smoke (Group I) and 141 (24.4%) reported posed. The exposure to ETS was quantified by calculating a cumula- exposure to ETS from the husband and other family members tive “exposure index”, which was a product of the number of smok- (Group II). The mean age of the pregnant women, in both the ers in the house to whom the case was exposed, average number of groups, was comparable. Table 1 shows the detailed compari- bidis/cigarettes smoked per day by them in the presence of the case son of all the maternal variables studied in the two groups. and the period of gestation in weeks. For the purpose of studying The women exposed to ETS had higher parity and a greater dose response, the exposed group was divided into four categories number of live births as compared to women not exposed to according to the quartiles of the exposure index. ETS. The women exposed to ETS were less educated as com- Preterm birth was defined as delivery at 37 weeks of gestation or less. pared to those not exposed to ETS (11.3% vs. 4.8% illiterates and 16.3% vs. 45% graduates or above, respectively) and fewer A small-for-gestation baby was defined as birth weight less than 10th were employed. Among the antenatal problems, there was a percentile of weight for that gestational age. significantly higher incidence of anaemia among the group exposed to ETS (P=0.003). The median exposure index in the Low birth weight (LBW) was defined as birth weight less than 2.50 kg. study group was 115.8 (range 31 to 2880, inter-quartile range Pregnancy-induced hypertension (PIH) in the antenatal period was 133.5). defined as two records of systolic blood pressure of 140 mmHg or above and/ or diastolic blood pressure of 90 mmHg or above at least There was no significant difference in the mean period of ges- 6 hours apart after 20 weeks of gestation. tation, however the incidence of pre-term birth was signifi- cantly higher among the women exposed to ETS (Table 2). Anaemia was defined as haemoglobin concentration less than 11 gm/ The onset of labour (spontaneous or induced) and the mode dl in the first and third trimester or haemoglobin concentration less of delivery (vaginal or caesarean section) were similar in the than 10.5 gm/dl in the second trimester. two groups. More babies born to mothers exposed to ETS were SPSS (Ver 10.0) was employed for data analysis. Unpaired Student t- small-for-gestation and their mean birth weight was 138 g less test was used for the comparison of continuous variables and Fish- than that of babies in the unexposed group of mothers (2632 Table 1: Antenatal profile of mothers exposed to environmental tobacco smoke vis-à-vis not exposed mothers Characteristics ETS not exposed (n=435) ETS exposed (n=141) P value Age: years Mean (SD) 25.34 (3.62) 25.90 (4.26) 0.131 Pregnancies: Mean + SD Gravida 1.75 + 0.25 2.08 + 1.47 0.003 Abortions 0.99 + 0.97 0.33 + 0.97 0.240 Live 0.56 + 0.40 1.17 + 0.70 0.004 Education: <0.001 Illiterate 21 (4.8) 16 (11.3) School Only 218 (50.1) 102 (72.3) University Graduate 196 (45.1) 23 (16.3) Occupation: 0.007 Employed 58 (13.3) 8 (5.7) Not employed 377 (86.7) 133 (94.3) Residence Rural 157 (36.1) 60 (42.6) Urban 278 (63.9) 81 (57.4) 0.101 Antenatal Problems Hypertension 88 (20.2) 23 (16.3) 0.221 Anaemia 128 (29.4) 60 (42.6) 0.003 Abruptio-placentae 2 (0.5) 0 0.570 Placenta Praevia 4 (0.9) 0 0.324 Exposure Index*Median (Range) – 115.8 (31-2880) *Exposure index: product of number of smokers in the house to whom the case was exposed, average number of bidis/cigarettes smoked per day by them in the presence of the subject and the period of gestation in weeks.