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Article Excerpt
DURING ADOLESCENCE, drinking, smoking, and use of illicit drugs are associated with risky sexual behaviors strongly predictive of teenage childbearing (for a review, see National Center on Addiction and Substance Abuse at Columbia University [CASA], 1999). Compared with abstaining peers, substance-using adolescents initiate sexual intercourse at younger ages (Harvey and Spigner, 1995; Kowaleski-Jones and Mott, 1998; Mott et al., 1996; Mott and Haurin, 1988; Small and Luster, 1994), have more frequent sexual intercourse (Poulin and Graham, 2001) with more sexual partners (Duncan et al., 1999; Howard and Wang, 2004; Lowry et al., 1994; Santelli et al., 1998; Shrier et al., 1997), and are less consistent in use of contraception (Fergusson and Lynskey, 1996; Fortenberry et al., 1997; Hingson et al., 1990; Poulin and Graham, 2001; Richter et al., 1993).
Although risks for very early reproduction are well documented, reproductive impairments associated with continued substance use may work to delay reproduction. Even moderate alcohol consumption by women is associated with menstrual disruptions, such as irregular and anovulatory cycles, sexual difficulties, and gynecological and obstetrical problems, including infertility and fetal loss (Abel, 1997; Hakim et al., 1998; Jensen et al., 1998; Kesmodel et al., 2002; Mendelson and Mello, 1998; Ryback, 1977; Wilsnack et al., 1984). In addition to menstrual disruptions (Windham et al., 1999), women who smoke show delayed conception or time to pregnancy and are at increased risk for infertility and fetal loss (Augood et al., 1998; Baird and Wilcox, 1985; Bolumar et al., 1996; Hughes and Brennan, 1996; Hull et al., 2000; Joffe and Zhimin, 1994). Similar risks from illicit drug use are also reported (Gold, 1997; Hall and Solowji, 1997; Jaffe et al., 1997).
To the extent that partners of substance-using women are also more likely to drink, smoke, or use illicit drugs (Agrawal et al., 2006; Labouvie, 1996; Yamaguchi and Kandel, 1993), such risks may be compounded. Reproductive impairments are observed in men who drink but often at higher levels of consumption. Heavy- or chronic-drinking men have lower sperm count and sperm motility, higher numbers of abnormal sperm, and higher rates of impotence (O'Farrell et al., 1998; Wright et al., 1991). Smoking reduces sperm count and sperm motility and also is associated with sperm abnormalities and impotence (Feldman et al., 1994; Vine, 1996), with similar risks observed in men who use illicit drugs (Buffum, 1982; Gold, 1997; Grinspoon and Bakalar, 1997; Jaffe et al., 1997; Wilson, 1991).
In addition, interpersonal difficulties associated with substance use may limit opportunities for reproduction regardless of reproductive impairments. Compared with light drinkers or abstainers, heavy or problem drinkers report more partner conflict and relationship dissatisfaction (Leonard and Eiden, 2007; Whisman, 2007); they are less likely to marry and, if they do, more likely to divorce, as are users of illicit drugs (Amato and Rogers, 1997; Chilcoat and Breslau, 1996; Hajema and Knibbe, 1998; Newcomb, 1994; Power et al., 1999; Temple et al., 1991; Yamaguchi and Kandel, 1997). Individuals who smoke are also more likely to divorce (Doherty and Doherty, 1998), especially those who initiate smoking during adolescence (Chassin et al., 1992).
To date, a single study has examined reproductive timing as a function of substance use or disorder. Waldron et al. (2008) examined associations between lifetime history of alcohol dependence (AD) and timing of first childbirth using data from two Australian twin cohorts, including 5,514 respondents born between 1893 and 1964 and 6,129 respondents born between 1964 and 1971. Little to no effect of AD on reproductive timing was found in men. However, for women in the older cohort, AD was associated with a 73% reduced likelihood of first childbirth but only after age 29. For women in the young cohort, AD was associated with delayed reproduction after age 24, with 40% reduced likelihood of first childbirth. Adjusting for sociodemographic characteristics, history of regular smoking, psychopathology, and family and childhood risks reduced effects only slightly.
Although findings of reproductive delay in alcoholic women are consistent with impairments to reproductive ability and/or opportunity, results are striking given that early alcohol use is a strong predictor of future alcohol problems, including AD (Grant and Dawson, 1997), and, as reviewed, adolescent substance use is associated with risk for early childbearing. Also striking are results for regular smoking, included as a control variable. Despite high comorbidity between problem use of alcohol and cigarettes (Grucza and Beirut, 2006; Madden et al., 2000), Waldron et al. (2008) found the opposite pattern for regular smoking coded without regard to nicotine dependence (ND). Regular smoking was associated with earlier reproduction in women from both cohorts and in men from the younger cohort, adjusting for the effects of AD and other control variables.
Although many regular smokers meet criteria for ND, whether the same pattern of earlier childbearing holds for ND or smoking without progression to regular smoking is unknown. In the present study, we examine unique effects of ever smoking, regular smoking, and ND on age at first childbirth in models unadjusted and adjusted for important correlates of both substance use and reproductive timing, including other substance use or disorder. We further extend previous work by examining effects of cannabis and other illicit drug use on reproductive onset.
Method
Participants
Respondents were twins born between 1964 and 1971 who were drawn from a broadly representative volunteer twin panel that is maintained by the Australian National Health and Medical Research Council. Twins are of primarily European descent and reflect the predominantly white Australian population from which the cohort was ascertained (see Heath et al., 2001; Knopik et al., 2006). Twins were ascertained through their parents in response to flyers distributed throughout Australian schools during 1980-1982 (Heath et al., 2001). During the period 1990-1992, 8,536 twins were contacted and asked to complete a brief self-report questionnaire. Questionnaires were returned by 5,058 individual twins (59% individual response rate), including 2,270 pairs (53% pairwise response rate). Excluding pairs that could not be located or in which either twin was deceased or too impaired to give informed consent, 8,020 twins (4,010 pairs) were contacted again between 1996 and 2000 for interview assessment. During this period, structured diagnostic interviews were administered to 6,257 twins, including 2,723 pairs (78% individual and 68% pairwise response rates).
Twins were selected for analysis if they had data on (1) variables used to code reproductive onset and (2) lifetime substance use or disorder, specifically, history of smoking, regular smoking, ND, and/or cannabis and other illicit drug use. Of 6,257 interviewed twins, 6,137 (98%) had data on both reproductive onset and at least one substance class, including 3,386 female and 2,751 male respondents. Age at interview of selected twins ranged from 22 to 36 years (mean [SD] = 30.42 [2.45]).
Measures
Twins completed an abbreviated telephone adaptation of the Semi-Structured Assessment of the Genetics of Alcoholism (SSAGA; Bucholz et al., 1994; Hesselbrock et al., 1999). The SSAGA was developed for the Collaborative Study on the Genetics of Alcoholism (COGA) to assess physical, psychological, and social manifestations of alcohol abuse or dependence and related psychiatric disorders in adults and is based on previously validated research interviews. Trained interviewers, who were supervised by a project coordinator and clinical psychologist, administered all interviews. Interviews were tape-recorded and a random sampling of tapes was reviewed for quality control and coding inconsistencies. Informed consent was obtained from all participants before their participation using procedures approved by the institutional review boards at both Washington University School of Medicine and Queensland Institute of Medical Research. A summary of individual measures follows, with descriptive statistics presented in Table 1 by respondent gender.
Reproductive onset. For respondents reporting biological children, age at first childbirth was computed by subtracting respondent's date of birth from the date of birth of his or her firstborn child.
Smoking history. Dummy variables for ever smoking, regular smoking, and ND were computed, with never smokers comprising the reference group. Respondents who reported having "tried" a cigarette were coded positive for ever smoking, with age at onset (in years) defined as age at first cigarette. Regular smoking was coded if respondents reported ever in their lifetime (1) having smoked 100 or more cigarettes or (2) smoking less than 100 but more than 20 cigarettes, and having smoked at least 1 or 2 days per week for a period of 3 weeks or more. Age at onset of regular smoking was defined as age first smoked at least 1 or 2...
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