Why do women douche? Results from a qualitative study.

OBJECTIVES: To explore women's attitudes and practices related to douching. METHODS: We conducted focus groups between July and December 1999 with 34 black and 27 white women enrolled in a managed care plan in Memphis, Tennessee. Participants were at least 18 years of age and had douched at some time in their lives. Five groups were held with black women and five with white women. RESULTS: The focus groups identified 13 themes that fell in four broad categories: general perceptions about feminine hygiene, douching behavior, factors perpetuating douching, and health information. Each of these categories is briefly discussed with supporting evidence. CONCLUSIONS: First, women have deeply-rooted beliefs about the critical role of douching in making them feel clean. Second, douching generally starts at a young age and is reinforced by family, friends, and the media. Third, douching is a very difficult behavior to change; any efforts to influence this behavior must consider women's beliefs and the media marketing efforts that promote douching. Finally, simplistic interventions that only provide risk information about douching are not likely to result in behavior change.

Effects of smoking reduction during pregnancy on the birth weight of term infants.

This study was undertaken to determine 1) whether reducing tobacco exposure during pregnancy increases the birth weight of term infants and 2) the relative effects of early- and late-pregnancy exposure to tobacco on infant birth weight. Data were obtained from the Smoking Cessation in Pregnancy project, conducted in public clinics in three states (Colorado, Maryland, and Missouri) between 1987 and 1991. Self-reported cigarette use and urine cotinine concentration were collected from 1,583 pregnant smokers at study enrollment and in the third trimester. General linear models were used to generate mean adjusted birth weights for women who reduced their tobacco exposure by 50 percent or more and for those who did not change their exposure. Regression smoothing techniques were used to characterize the relation between birth weight and early exposure and birth weight and third-trimester exposure. Reducing cigarette use was associated with an increase in mean adjusted birth weight of only 32 g, which was not significant (p = 0.33). As third-trimester cigarette use increased, birth weight declined sharply but leveled off at more than eight cigarettes per day. Findings were similar when urine cotinine concentration was used. Women who smoke during pregnancy may need to reduce to low levels of exposure (less than eight cigarettes per day) to improve infant birth weight.

Measures of maternal tobacco exposure and infant birth weight at term.

This study was undertaken to determine the relation between self-reported number of cigarettes smoked per day and urine cotinine concentration during pregnancy and to examine the relations between these two measures of tobacco exposure and birth weight. Data were obtained from the Smoking Cessation in Pregnancy project, conducted between 1987 and 1991. Cigarette smoking information and urine cotinine concentration were collected for 3,395 self-reported smokers who were receiving prenatal care at public clinics in three US states (Colorado, Maryland, and Missouri) and who delivered term infants. General linear models were used to quantify urine cotinine variability explained by the number of cigarettes smoked per day and to generate mean adjusted birth weights for women with different levels of tobacco exposure. Self-reported number of cigarettes smoked per day explained only 13.9% of the variability in urine cotinine concentration. Birth weight declined as tobacco exposure increased; however, the relation was not linear. The sharpest declines in birth weight occurred at low levels of exposure. Furthermore, urine cotinine concentration did not explain more variability in birth weight than did number of cigarettes smoked. These findings should be considered by researchers studying the effects of smoking reduction on birth outcomes.

Superior role of apolipoprotein B48 over apolipoprotein B100 in chylomicron assembly and fat absorption: an investigation of apobec-1 knock-out and wild-type mice.

Editing of apolipoprotein (apo)-B100 mRNA to yield apo-B48 is a specific and developmentally regulated step in enterocytes of mammals. However, the functional significance of this step is not known. Since mice containing only apo-B100 have not been documented to exhibit any difference in intestinal fat absorption from wild-type mice, the evolutionary advantage of apoB mRNA editing has been questioned. In the present study, we have compared fat absorption and chylomicron assembly in apobec-1 knock-out (KO) or wild-type (WT) mice subjected to different dietary manipulations: low-fat chow, a fat-enriched 'Western' diet and overnight fasting. Experiments in vivo and in vitro revealed differences in the ability of KO and WT enterocytes to assemble and secrete chylomicrons under different dietary conditions. After overnight fasting, chylomicron secretion is reduced considerably in KO compared with WT enterocytes. This is not due to reduced synthesis of apo-B or triacylglycerol (TAG), but appears to be a result of impaired assembly of chylomicrons, so that triacylglycerol accumulates in the enterocytes. After feeding with fat, secretion of chylomicrons enriched in pre-existing TAG is stimulated in KO compared with WT mice. In the present study, we have documented for the first time that apo-B100 is considerably less efficient than apo-B48 in exerting its role in the early stage of chylomicron assembly, which is rate-limiting under conditions of low dietary fat. However, this impairment is overcome by increased TAG stores that stimulate later stages in assembly, which are rate-limiting in the fat-fed state. apo-B mRNA editing may result in more efficient fat absorption, specifically under conditions of food shortage or low-fat content, and thus provide an evolutionary advantage.

Preventing adverse sequelae of bacterial vaginosis: a public health program and research agenda.

BACKGROUND: The cause of bacterial vaginosis remains poorly understood. Recent evidence strengthens the association between bacterial vaginosis and serious medical complications. GOAL: To review the evidence linking bacterial vaginosis with adverse pregnancy outcomes, complications after gynecologic procedures, and HIV infection, and to identify prevention strategies. METHODS: In March 1999, the Centers for Disease Control and Prevention organized a conference to accomplish this goal. RESULTS: Better understanding is needed concerning the etiology, epidemiology, and natural history of bacterial vaginosis. More efficacious treatment of bacterial vaginosis and strategies to reduce maternal complications associated with bacterial vaginosis, such as premature rupture of the fetal membranes, chorioamnionitis, premature labor and delivery, postdelivery endometritis, and postpartum infant complications should be developed. Recent evidence shows that screening and treatment of bacterial vaginosis before abortion reduces postabortion pelvic inflammatory disease, and that anaerobic coverage during hysterectomy reduces postoperative complications. Better understanding concerning the relation of bacterial vaginosis to acquisition of sexually transmitted diseases and HIV infection are needed as well as possible prevention strategies. CONCLUSIONS: A national prevention effort should be guided by the results of research that addresses current knowledge gaps.

Vaginal douching and preterm birth: an intriguing hypothesis.

The rate of preterm birth has risen in recent years and is twice as high among black women as among white women. Neither the underlying causes nor the reasons for the racial disparity are clearly understood. Further, preventable risk factors have not been identified. We hypothesize that vaginal douching plays a key role in the risk of infection-related spontaneous preterm birth. Vaginal douching is a common behavior, twice as prevalent among black women as among white women. Douching may be an important mechanism by which vaginal pathogens gain access to the upper genital tract. Douching increases the risk of acquiring bacterial vaginosis. It may also facilitate the ascent of microorganisms into the upper genital tract, resulting in a chronic bacterial colonization inside the uterus. During pregnancy, the host inflammatory response is initiated, which stimulates preterm labor and birth. Douching, a potentially preventable risk factor, may explain a substantial proportion of the black-white disparity in preterm birth.

Are interpregnancy intervals between consecutive live births among black women associated with infant birth weight?

OBJECTIVES: The purpose of this study was to determine whether the length of interpregnancy intervals between consecutive live births among Black women had any significant effect on mean birth weight as had previously been reported in another study. DESIGN: We examined a sample (1,048 women, 66% of study participants) from a study of non-Hispanic Black women whose infants were born at a large, inner-city, public hospital in Georgia from October 1988 through August 1990. Data were evaluated for the 494 women whose current and immediately previous pregnancies ended in the birth of a live infant weighing 500 grams or more. METHODS: Linear regression and analysis of covariance models were developed. RESULTS: The median interpregnancy interval was 15 months (range 1 to 207 months), with 19 (4%) of the women having intervals of less than 3 months. After adjustment for parity, gestational age (in weeks), and smoking status, the mean birth weight associated with an interpregnancy interval of three or more months was 3,106 grams, 215 grams greater than that for an interval of less than three months (P = .06). CONCLUSIONS: Although longer birth spacing has been associated with certain positive social and health effects, the population attributable effect on infant birth weight may not be very significant.

Unintended pregnancy among adult women exposed to abuse or household dysfunction during their childhood.

CONTEXT: Studies have identified childhood sexual and physical abuse as a risk factor for adolescent pregnancy but the relationship between exposure to childhood abuse and unintended pregnancy in adulthood has, to our knowledge, not been studied. OBJECTIVE: To assess whether unintended pregnancy during adulthood is associated with exposure to psychological, physical, or sexual abuse or household dysfunction during childhood. DESIGN AND SETTING: Analysis of data from the Adverse Childhood Experiences Study, a survey mailed to members of a large health maintenance organization who visited a clinic in San Diego, Calif, between August and November 1995 and January and March 1996. The survey had a 63.4% response rate among the target population for this study. PARTICIPANTS: A total of 1193 women aged 20 to 50 years whose first pregnancy occurred at or after age 20 years. MAIN OUTCOME MEASURE: Risk of unintended first pregnancy by type of abuse (psychological, physical, or sexual abuse; peer sexual assault) and type of household dysfunction (physical abuse of mother by her partner, substance abuse by a household member, mental illness of a household member). RESULTS: More than 45% of the women reported that their first pregnancy was unintended, and 65.8% reported exposure to 2 or more types of childhood abuse or household dysfunction. After adjustment for confounders (marital status at first pregnancy and age at first pregnancy), the strongest associations between childhood experiences and unintended first pregnancy included frequent psychological abuse (risk ratio [RR], 1.4; 95% confidence interval [CI], 1.2-1.6), frequent physical abuse of the mother by her partner (RR, 1.4; 95% CI, 1.1-1.7), and frequent physical abuse (RR, 1.5; 95% CI, 1.2-1.8). Women who experienced 4 or more types of abuse during their childhood were 1.5 times (95% CI, 1.2-1.8) more likely to have an unintended first pregnancy during adulthood than women who did not experience any abuse. CONCLUSIONS: This study indicates that there may be a dose-response association between exposure to childhood abuse or household dysfunction and unintended first pregnancy in adulthood. Additional research is needed to fully understand the causal pathway of this association.

Dietary fish oils inhibit early events in the assembly of very low density lipoproteins and target apoB for degradation within the rough endoplasmic reticulum of hamster hepatocytes.

Dietary fish oils inhibited secretion and stimulated intracellular degradation of apolipoprotein (apo)B in hamster hepatocytes, while dietary sunflower oils stimulated secretion and had no effect on degradation of apoB. To investigate the intracellular site at which fish oils act, we have made use of our previous observations that inhibition of degradation by N-acetyl-leucyl-leucyl-norleucinal (ALLN) results in accumulation of apoB in the trans -Golgi membrane and does not stimulate secretion, while inhibition of degradation by o-phenanthroline results in accumulation of apoB in the rough endoplasmic reticulum membrane and stimulates secretion. Thus, ALLN protects apoB which has been diverted from secretion and o -phenanthroline protects apoB which is targetted for secretion. Addition of o -phenantholine to the incubation medium of hepatocytes from fish oil-fed hamsters inhibited degradation of apoB and stimulated its secretion in particles of the density of VLDL, while addition of ALLN had no effect. These observations suggest that dietary fish oils reversibly inhibit early steps in the assembly of very low density lipoprotein precursors and target apoB for degradation in the rough endoplasmic reticulum.

The risk of low birth weight associated with vaginal douching.

OBJECTIVE: To examine the association between vaginal douching and low birth weight (LBW) after accounting for known risk factors. METHODS: We used cross-sectional interview data from the 1988 National Survey of Family Growth, a nationally representative sample of 4665 women of child-bearing age and 11,553 singleton live births. We compared the risk of LBW among women who reported they douched regularly with the risk among women who did not douche, after controlling for potential confounders including maternal age, race, household income, marital status, total number of pregnancies, smoking, alcohol use, drug use during the pregnancy, year of birth of each infant, geographic region, and self-reported history of pelvic inflammatory disease. RESULTS: In multivariate analysis, regular douching was associated with an increased risk of LBW (adjusted odds ratio [OR], 1.29; 95% confidence interval [CI] 1.06, 1.57). Frequency of douching and LBW exhibited a dose-response. The adjusted OR for the association between daily douching and LBW was 2.49 (95% CI 1.23, 5.01) compared with an adjusted OR of 1.13 (95% CI 0.83, 1.55) for the association between monthly douching and LBW. There was no racial difference in the risk of LBW associated with douching. CONCLUSION: These preliminary data suggest an association between douching and LBW risk. If these findings are replicated in future studies, douching may represent a major preventable risk factor for LBW.

Completeness of ascertainment of prenatal smoking using birth certificates and confidential questionnaires: variations by maternal attributes and infant birth weight. PRAMS Working Group. Pregnancy Risk Assessment Monitoring System.

Birth certificate data frequently are used to monitor the prevalence of smoking during pregnancy. The authors used a two-sample capture-recapture method to estimate the completeness of ascertainment of prenatal smoking on birth certificates and on confidential questionnaires in six US states. Completeness of ascertainment was also examined according to maternal attributes and infant birth weight. The samples included white women who delivered a live infant between 1993 and 1995 in one of six states (Alabama, Alaska, Georgia, Maine, South Carolina, or West Virginia) and who responded to a questionnaire mailed to them 2-6 months postpartum as part of the Pregnancy Risk Assessment Monitoring System. State-specific sample sizes ranged from 2,647 to 4,795. The completeness of ascertainment ranged from 70.6% to 82.0% using birth certificates and from 86.2% to 90.3% using confidential questionnaires. In all six states, the birth certificates' completeness of ascertainment varied by maternal education and infant birth weight, and the questionnaires' completeness varied by maternal age. Both birth certificates and questionnaires underestimated the true extent of smoking during pregnancy among these white women. Differential reporting by birth weights recorded on birth certificates would result in an overestimated association between low birth weight and prenatal smoking.

Regulation of the assembly and secretion of very low density lipoproteins by the liver.

Recent studies have suggested that there are three sites at which VLDL secretion by the liver may be controlled: (i) Newly synthesised apo-B either remains associated with the RER membrane and is degraded by the ubiquitin/proteasome system, or is translocated into the lumen and incorporated into lipid poor VLDL precursors; (ii) the lumenal apo-B is either degraded or moves on, and (iii) acquires the remaining VLDL lipids in the SER/cis-Golgi. Newly synthesised apo-B, at the cytosolic side of the RER, is stabilised and protected from degradation by the chaperone protein, hsp-70. Triacylglycerol, cholesterol ester and phospholipids have all been implicated in the translocation of apo-B and microsomal triglyceride protein plays a major role. If translocation does not occur then the apo-B is degraded. Dietary fish-oils, but not sunflower oil, inhibit movement of apo-B containing precursors from the RER and their assembly with lipids and target lumenal apo-B to degradation. This effect is reversed by inhibition of lumenal proteolysis, but not by inhibition of cytosolic proteolysis. Therefore lumenal degradation of apo-B and secretion appear to be in balance, so that if assembly of VLDL precursors is slowed, then degradation becomes predominant. If however, degradation is inhibited then VLDL assembly can proceed. These observations suggest that movement of VLDL precursors from the RER lumen to the second stage of assembly may be a further regulated step.

Cigarette smoking as a risk factor for ectopic pregnancy.

OBJECTIVE: Our purpose was to assess the risk of ectopic pregnancy among women who smoke cigarettes. STUDY DESIGN: We used data from a case-control study of ectopic pregnancy conducted from October 1988 to August 1990 at an inner-city hospital in Georgia. Cases were 196 non-Hispanic black women with a surgically confirmed ectopic pregnancy. Controls were non-Hispanic black women who had delivered either a live or a stillborn infant weighing at least 500 gm (n = 882) or who were pregnant and seeking an induced abortion (n = 237). RESULTS: After we adjusted for parity, douching history, history of infertility, and age, the odds ratio for ectopic pregnancy was 1.9 (95% confidence interval 1.4 to 2.7) for women who smoked during the periconception period compared with women who did not smoke at that time. After stratification by the amount of daily smoking during the periconception period, the odds ratio rose from 1.6 (95% confidence interval 0.9 to 2.9) for women who smoked 1 to 5 cigarettes to 1.7 (95% confidence interval 1.1 to 2.8) for women who smoked 6 to 10 cigarettes to 2.3 (95% confidence interval 1.3 to 4.0) for women who smoked 11 to 20 cigarettes, and to 3.5 (95% confidence interval 1.4 to 8.6) for women who smoked >20 cigarettes per day. CONCLUSION: In this inner-city population, cigarette smoking was an independent, dose-related risk factor for ectopic pregnancy among black women. The public health and medical care communities should inform the public of this additional risk associated with cigarette smoking and intensify intervention strategies to reduce cigarette smoking among women of reproductive age.

Multiple induced abortions as risk factor for ectopic pregnancy. A prospective study.

OBJECTIVE: To assess the risk of ectopic pregnancy by the number of previous induced abortions. DESIGN: Prospective cohort study. METHODS: Three thousand seven hundred and fifty-four women, 39 years old or younger, living permanently in one Norwegian county, who had had at least one induced abortion between January 1, 1987 and December 31, 1992, at the University Hospital of Trondheim, Norway were followed prospectively for histologically verified ectopic pregnancies until December 31, 1993. Exposure time was measured from the most recent induced abortion (index abortion) until the ectopic pregnancy, closure date, or the subject's 40th birthday. Statistical analyses were done in SAS applying survival analyses and poisson regression. RESULTS: During the follow-up period of 164,167 women-months, we observed 24 ectopic pregnancies in 3,754 women. The adjusted incidence density ratio (aIDR) for women who had had two or more induced abortions was 1.2 (95% CI: 0.5-3.1) in comparison with the reference group of women who had had one induced abortion. Measuring exposure as increasing number of consecutive induced abortions, no dose-response to ectopic pregnancy was found between two consecutive (aIDR 0.9) and three or more consecutive abortions (aIDR 1.1) in comparison with the reference group. CONCLUSION: In our setting, no excess risk of ectopic pregnancy was associated with multiple previous induced abortions compared with one previous induced abortion.

PIP: To assess the association between induced abortion and subsequent ectopic pregnancy, 3754 Norwegian women 39 years or younger who had at least one induced abortion at the University Hospital of Trondheim during 1987-92 were followed for histologically confirmed ectopic pregnancies through the end of 1993. In a total of 164,167 woman-months of follow-up, 24 ectopic pregnancies were recorded. No woman had more than one ectopic pregnancy. The overall cumulative incidence of ectopic pregnancy among women with an induced abortion history rose from 3.5 per 1000 women at 1 year to 11.1 per 1000 women at 6 years of follow-up. The adjusted incidence density ratio (aIDR) for women with 2 or more induced abortions was 1.2 (95% confidence interval, 0.5-3.1). No dose-response to ectopic pregnancy was found between 2 consecutive (aIDR, 0.9) and 3 or more consecutive (aIDR, 1.1) abortions compared with the reference group. Ectopic pregnancy after the most recent abortion was more likely to occur among women whose first pregnancy ended as an ectopic one than among those whose first pregnancy resulted in a birth. Although the results of longer-term follow-up of this cohort of Norwegian women have not yet been analyzed, the present findings suggest that induced abortion does not increase the risk of ectopic pregnancy.

Vaginal douching and the risk of ectopic pregnancy among black women.

OBJECTIVE: Our goal was to determine whether vaginal douching was associated with ectopic pregnancy among black women and whether specific douching behaviors were associated with differences in risk. STUDY DESIGN: We analyzed data from a case-control study of ectopic pregnancy conducted between October 1988 and August 1990 at a major public hospital in Atlanta, Georgia. Case subjects were 197 black women with surgically confirmed ectopic pregnancies; the control group included 882 black women who were delivered of live or stillborn infants and 237 black women who were seeking to terminate a pregnancy. RESULTS: The adjusted odds ratio for ectopic pregnancy associated with ever having douched was 3.8 (95% confidence interval 1.6 to 8.9). The risk increased with increasing number of years of douching at least once per month. No douching behavior was found to be without risk; even women who douched for routine cleanliness were at increased risk of ectopic pregnancy. CONCLUSIONS: Vaginal douching is a modifiable behavior that may greatly increase a woman's risk of ectopic pregnancy.

The relation between induced abortion and ectopic pregnancy.

OBJECTIVE: To determine whether having had one or more induced abortions increases a woman's risk of having an ectopic pregnancy. METHODS: We conducted a case-control study of all women admitted to a major metropolitan hospital in Georgia with a surgical diagnosis of ectopic pregnancy during the period of October 1988 to August 1990. Controls were randomly selected from women seeking an induced abortion or delivering an infant at the same hospital. After exclusions, this analysis included 182 cases and 1056 controls. Stratified analysis and unconditional logistic regression were used to control for confounding and to estimate the relative risks. RESULTS: Approximately 90% of cases and controls were non-Hispanic, black women; 34% of the cases and 36% of the controls reported a history of induced abortion. The crude odds ratio for having an ectopic pregnancy associated with a history of induced abortion was 0.9 (95% confidence interval 0.6, 1.3). The odds ratio remained the same after adjusting for selected confounding variables and stratifying by the number of induced abortions, gestational age at the time of abortion, place where the abortion was performed, and the woman's report of medical complications of the abortion. CONCLUSION: We found no evidence that having one or more induced abortions increases a woman's risk of having an ectopic pregnancy.

Investigation of the role of lipids in the assembly of very low density lipoproteins in rabbit hepatocytes.

Our aims were i) to determine which lipids colocalize with newly synthesized apolipoprotein (apo) B in the lumen of the rough endoplasmic reticulum (RER), and thus may play a role in the stabilization and/or translocation of this protein; and ii) to determine the intracellular sites of assembly of lipids into very low density lipoprotein (VLDL). In order to do this, we have developed a new method for the separation of ER-derived microsomes on self-generated gradients of iodixanol. Rabbit liver microsomes were resolved into two broad peaks, the lighter peak contained smooth vesicles and the heavier peak contained rough vesicles. Each peak was collected in a number of subfractions. A single gradient thus separates the initial events in the secretion process (RER fractions), from later events (smooth endoplasmic reticulum (SER) fractions). The microsomal fractions were separated into membranes and lumenal contents, and the mass of apoB and VLDL lipids determined by ELISA or high performance thin-layer chromatography, respectively. The biosynthetic relationships of apoB and lipids were investigated, in timed or chase experiments, by incubation of isolated rabbit hepatocytes with radiolabeled precursors of apoB or lipids, followed by isolation and analysis of the microsomal fractions. The results indicate that very small amounts of triacylglycerol, cholesterol, and cholesteryl ester co-localize with apoB into the lumen of the RER. The bulk of the VLDL lipids were in the lumen of the SER. However, some newly synthesized triacyl-glycerol, phospholipid, cholesterol, and cholesteryl ester were also transferred to the lumen of the RER and were chased into the SER lumen. Double-labeling experiments showed that cholesteryl ester produced from newly synthesized cholesterol (labeled with [3H]mevalonate and [14C]oleate) was almost exclusively present in the RER, while cholesteryl ester in the SER was labeled only with [14C]oleate. Thus, distinct intracellular lipid-pools may be involved at different stages in the assembly of VLDL.

Increasing incidence of ectopic pregnancy in one Norwegian county--a population based study, 1970-1993.

OBJECTIVE: To estimate time trends related to ectopic pregnancy while considering the contribution of repeat ectopic pregnancy and changing treatment for infertile couples over the past 24 years. METHODS: Population based incidence data on ectopic pregnancy were collected from the only two hospitals in one Norwegian county from 1970 through 1993. Cases were identified through hospital discharge registries and all medical records were reviewed. Only females, aged 15-44 years, living permanently in the county and having a histologically verified ectopic pregnancy were eligible for the study. Data were analyzed in 5-year periods and 5-year age-groups. RESULTS: The incidence of ectopic pregnancy (per 1,000 woman-years) increased fourfold from the first to the last period. When we restricted the analyses to women with no previous ectopic pregnancy and no previous infertility surgery or treatment, we observed a linear threefold increase in the number of ectopic pregnancies. CONCLUSIONS: Repeat ectopic pregnancy and increased infertility treatment in the late 1970s and early 1980s might explain at most 25% of the increase in the incidence of ectopic pregnancy. After 1985, assisted reproduction might contribute to 4-5% of ectopic pregnancies diagnosed. The introduction of laparoscopy might explain some of this increase in the 1970s; however, we doubt that the introduction of more sensitive pregnancy tests or vaginal ultrasound in the 1980s contributed to the observed increase in ectopic pregnancy.

Women and smoking: an update for the 1990s.

Cigarette smoking is associated with many health hazards, ranging from lung cancer to low infant birth weight. In the United States in 1994, 23.1% of all women and 14.6% of pregnant women smoked. Few physicians ask their patients about smoking, although minimal effort by physicians could help many smokers to quit. This article summarizes the current data on smoking prevalence, reviews quitting techniques, covers topics of particular interest to physicians caring for women, and suggests ways in which physicians may become more active in preventing smoking among teens.