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Risk of ectopic pregnancy in black women increased with number of cigarettes smoked
GY N ECO L OG Y
Risk of ectopic pregnancy in black women increased with number of cigarettes smoked Saraiya M, Berg CJ, Kendrick JS, Strauss LT, Atrash HK, Ahn YW. Cigarette smoking as a risk factor for ectopic pregnancy. Am J Obstet Gynecol 1998; 178: 493d498
OBJECTIVE To determine if there is an association between cigarette smoking and ectopic pregnancy in black women. DESIGN Case-control study. SETTING Inner-city hospital in the USA. PATIENTS The cases were 196 non-Hispanic black women aged 18–44 years with surgically confirmed ectopic pregnancy. Controls were a random sample of black women who delivered a live or stillborn baby weighing 5500 g (n"882) and black women seeking an induced abortion (n"237). Women with a history of ectopic pregnancy, tubal surgery or current IUD use were excluded. INTERVENTION A 1-hour interview questionnaire, seeking information about demographics, obstetric and medical histories, and personal habits including cigarette smoking, was administered to both cases and controls. MAIN OUTCOME MEASURES Odds ratio (OR, adjusted for other risk factors) for ectopic pregnancy in women who smoked
Commentary Proving a causal association between an exposure and outcome is often difficult, even when a large effect size exists, e.g. between smoking and lung cancer. When a randomized controlled trial is not feasible or ethical, as is the situation with an exposure like smoking, prospective cohort studies provide the most valid evidence from which conclusions can be drawn. With such a design, women are enrolled and their smoking status assessed, along with potential confounders for which adjustments can be made in the analyses, to allow for an assessment of the independent effect of the exposure. Unfortunately, important but unknown confounders may be more or less prevalent among exposed and unexposed individuals, and may lead to an erroneous conclusion of the effect of the exposure. A case-control design, as was used in the present study, is even more vulnerable to the influence of confounding. By definition, the cases (women with documented ectopic pregnancy) and controls (women delivering or requesting termination) are different in many potentially important ways, but one can only account for the known factors. An identifiable and potentially important difference between cases and controls in this study is the fact that 33% of potential controls were not available for interview, while only 19% of cases were unavailable d women with ectopic pregnancies are usually in hospital and more easily
^ 1999 Harcourt Brace & Co. Ltd
during the 6 months before and 1 month after the last menstrual period, compared to women who never smoked or smoked in the past. MAIN RESULTS Compared to controls, women with ectopic pregnancy were significantly more likely to be 525 years of age, to ever have been married or cohabited, to have a history of IUD use, infertility, vaginal douching or pelvic inflammatory disease, and to have had '4 sexual partners. Smoking in the periconceptual period was reported by 40.8% of the cases and 22.4% of the controls (OR 1.9, 95% CI 1.4–2.7). The risk of ectopic pregnancy increased with number of cigarettes smoked daily ( p"0.0002): 1–5/day (27% of smokers) OR 1.6 (CI 0.9–2.9), 6–10/day (42%) OR 1.7 (CI 1.1–2.8), 11–20/day (25%) OR 2.3 (CI 1.3–4.0), '20/day (6%) OR 3.5 (CI 1.4–8.6). CONCLUSION Cigarette smoking was associated with ectopic pregnancy in inner-city black women. The risk of ectopic pregnancy increased with number of cigarettes smoked.
tracked down. What if those who could not be tracked down tended to be less careful, reliable individuals who were often heavy smokers? A disproportionate absence of this subject type in the control group, compared to the case group, would tend to inflate apparent smoking among cases. Another potential problem is ‘recall bias’. Most of the controls had delivered and were asked to recall their exposure from 9 to 15 months ago. If many of them had reduced their smoking during pregnancy, they might tend to underestimate the amount of their exposure. Cases, on the other hand, were interviewed shortly after both exposure and event d the ectopic pregnancy. These women may not have reduced their smoking. Some may have even increased it because of stress. If they tended to overestimate their exposure, how would this affect the conclusion? Having said all of this, the authors have done an excellent job of considering and adjusting for known confounders, using logistic regression. Their most compelling findings suggesting a causal relationship between cigarette smoking and ectopic pregnancy are (1) the return to normal risk in former smokers and (2) the dosedresponse effect. However, with these relatively small effect sizes of 1d3, this study is best considered as hypothesis generating rather than conclusive. Edward G. Hughes, MB McMaster University, Hamilton, Canada
Evidence-based Obstetrics and Gynecology (1999) 1, 21
21
Risk of ectopic pregnancy in black women increased with number of cigarettes smoked Saraiya M, Berg CJ, Kendrick JS, Strauss LT, Atrash HK, Ahn YW. Cigarette smoking as a risk factor for ectopic pregnancy. Am J Obstet Gynecol 1998; 178: 493d498
OBJECTIVE To determine if there is an association between cigarette smoking and ectopic pregnancy in black women. DESIGN Case-control study. SETTING Inner-city hospital in the USA. PATIENTS The cases were 196 non-Hispanic black women aged 18–44 years with surgically confirmed ectopic pregnancy. Controls were a random sample of black women who delivered a live or stillborn baby weighing 5500 g (n"882) and black women seeking an induced abortion (n"237). Women with a history of ectopic pregnancy, tubal surgery or current IUD use were excluded. INTERVENTION A 1-hour interview questionnaire, seeking information about demographics, obstetric and medical histories, and personal habits including cigarette smoking, was administered to both cases and controls. MAIN OUTCOME MEASURES Odds ratio (OR, adjusted for other risk factors) for ectopic pregnancy in women who smoked
Commentary Proving a causal association between an exposure and outcome is often difficult, even when a large effect size exists, e.g. between smoking and lung cancer. When a randomized controlled trial is not feasible or ethical, as is the situation with an exposure like smoking, prospective cohort studies provide the most valid evidence from which conclusions can be drawn. With such a design, women are enrolled and their smoking status assessed, along with potential confounders for which adjustments can be made in the analyses, to allow for an assessment of the independent effect of the exposure. Unfortunately, important but unknown confounders may be more or less prevalent among exposed and unexposed individuals, and may lead to an erroneous conclusion of the effect of the exposure. A case-control design, as was used in the present study, is even more vulnerable to the influence of confounding. By definition, the cases (women with documented ectopic pregnancy) and controls (women delivering or requesting termination) are different in many potentially important ways, but one can only account for the known factors. An identifiable and potentially important difference between cases and controls in this study is the fact that 33% of potential controls were not available for interview, while only 19% of cases were unavailable d women with ectopic pregnancies are usually in hospital and more easily
^ 1999 Harcourt Brace & Co. Ltd
during the 6 months before and 1 month after the last menstrual period, compared to women who never smoked or smoked in the past. MAIN RESULTS Compared to controls, women with ectopic pregnancy were significantly more likely to be 525 years of age, to ever have been married or cohabited, to have a history of IUD use, infertility, vaginal douching or pelvic inflammatory disease, and to have had '4 sexual partners. Smoking in the periconceptual period was reported by 40.8% of the cases and 22.4% of the controls (OR 1.9, 95% CI 1.4–2.7). The risk of ectopic pregnancy increased with number of cigarettes smoked daily ( p"0.0002): 1–5/day (27% of smokers) OR 1.6 (CI 0.9–2.9), 6–10/day (42%) OR 1.7 (CI 1.1–2.8), 11–20/day (25%) OR 2.3 (CI 1.3–4.0), '20/day (6%) OR 3.5 (CI 1.4–8.6). CONCLUSION Cigarette smoking was associated with ectopic pregnancy in inner-city black women. The risk of ectopic pregnancy increased with number of cigarettes smoked.
tracked down. What if those who could not be tracked down tended to be less careful, reliable individuals who were often heavy smokers? A disproportionate absence of this subject type in the control group, compared to the case group, would tend to inflate apparent smoking among cases. Another potential problem is ‘recall bias’. Most of the controls had delivered and were asked to recall their exposure from 9 to 15 months ago. If many of them had reduced their smoking during pregnancy, they might tend to underestimate the amount of their exposure. Cases, on the other hand, were interviewed shortly after both exposure and event d the ectopic pregnancy. These women may not have reduced their smoking. Some may have even increased it because of stress. If they tended to overestimate their exposure, how would this affect the conclusion? Having said all of this, the authors have done an excellent job of considering and adjusting for known confounders, using logistic regression. Their most compelling findings suggesting a causal relationship between cigarette smoking and ectopic pregnancy are (1) the return to normal risk in former smokers and (2) the dosedresponse effect. However, with these relatively small effect sizes of 1d3, this study is best considered as hypothesis generating rather than conclusive. Edward G. Hughes, MB McMaster University, Hamilton, Canada
Evidence-based Obstetrics and Gynecology (1999) 1, 21
21