Binge Drinking in PregnancyFrequency and Methodology
Ulrik Kesmodel1
1 Current address: Department of Epidemiology and Social Medicine, University of Aarhus, 8000 Aarhus C, Denmark.
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ABSTRACT
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Independent of average alcohol intake, the effect of binge drinking on adverse pregnancy outcomes in humans is only sporadically reported, but most studies in humans have found little or no effect of binge drinking on several adverse pregnancy outcomes. In a representative sample of 371 pregnant Danish women, the agreement between two different measures of binge drinking during the first half of pregnancy obtained from interviews and questionnaires was assessed, and the frequency and pattern of binge drinking were described. The percentage of agreement between the methods ranged between 81% and 86%. The proportion of women who reported binge drinking depended on the definition of pregnancy, but the proportion peaked in week 3 measured from the last menstrual period and thereafter declined to approximately 1 percent in week 7. On the basis of this 1998 study, it is suggested that most human studies on binge drinking in pregnancy may have failed to find any association because of methodological problems. It is suggested that future studies should take into account the number of binge episodes as well as the time of binge drinking. This information may easily be obtained from most pregnant women by asking two questions in interviews or questionnaires.
alcohol drinking; bias (epidemiology); questionnaires; pregnancy
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INTRODUCTION
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In humans intake of about 1 drink/day or more has consistently been shown to be associated with a large number of adverse pregnancy outcomes (1
), as well as long-term effects including malformations (2
), mental retardation (3
), and behavioral and psychosocial problems in childhood and adolescence (4
, 5
). Almost all studies have assessed the risk on the basis of average alcohol intake per day or per week.
Animal models have suggested, however, that it is the peak blood alcohol concentration rather than the average intake that determines the level of damage (6
8
) and that brain growth is particularly susceptible to high blood alcohol concentrations (6
, 7
, 9
). High blood alcohol concentrations are achieved by intake of large volumes of alcohol on a single occasion. This behavior is called binge drinking, and in humans it is usually defined as intake of five or more standard drinks per occasion (10
).
In humans the effect of binge drinking independent of average alcohol intake is only sporadically reported. In one study population, binge drinking was found to be associated with learning disabilities, deficits in attention and memory, and an inflexible approach to problem solving at age 7.5 years (11
, 12
), but otherwise most studies have found little or no effect of binge drinking on birth weight (13
15
), length at birth (13
, 15
), head circumference (13
), gestational age (13
), Apgar score (13
), and malformations (16
, 17
).
In Denmark a fairly large proportion of pregnant women admit to episodes of binge drinking (18
). In this study among a representative sample of pregnant Danish women, the agreement between two measures of binge drinking during early pregnancy obtained from interviews and questionnaires is assessed, and the frequency and pattern of binge drinking during early pregnancy are described. The implications for etiologic studies on the association between binge drinking and adverse pregnancy outcomes are discussed.
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MATERIALS AND METHODS
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Setting
Almost all women in Denmark participate in the ante-natal care program. Danish-speaking pregnant women who had been referred to the Midwife Center in Aarhus, Denmark, for routine antenatal care were contacted at their first visit between October 15, 1998, and December 17, 1998. The women were interviewed about their drinking habits and knowledge about and attitudes toward alcohol intake during pregnancy. Interviews were performed by two specially trained midwives either immediately after the first antenatal care visit or, if this was not possible, on a day of the woman's own choice as soon as possible after the visit.
The Midwife Center in Aarhus is associated with the Department of Obstetrics and Gynaecology, Aarhus University Hospital. All Danish-speaking pregnant women attending routine antenatal care at the Department have been invited to participate in a cohort study. At the end of the first trimester when booking for delivery, women were asked to fill in a questionnaire on maternal characteristics, lifestyle factors, and obstetric history.
Data collection
In the interview and the questionnaire, the women were asked identical questions on binge drinking (table 1). The definition of a drink followed the definition of the Danish National Board of Health, one drink containing 12 g or 15 ml of pure alcohol, the equivalent of one normal beer, one glass of wine, 8 cl of fortified wine, or 4 cl of spirits. For the participants, the median gestational age when filling in the questionnaire was 11.0 weeks (10/90 percentiles = 8.4/16.9 weeks), and at the time of interview it was 15.0 weeks (10/90 percentiles = 13.5/18.3 weeks).
For 359 women, the gestational age when filling in the questionnaire and at interview was calculated from the last menstrual period adjusted for cycle length, and for the remaining women it was based on the best available clinical judgment at the time of the interview. Gestational age was calculated in weeks, week 1 starting on the first day of the last menstrual period. Three definitions of pregnancy were used for the subsequent analyses. First, pregnancy was defined as starting on the first day of the last menstrual period (week 1 onward). Second, pregnancy was defined as starting at the time of conception, which on average takes place approximately 2 weeks after the last menstrual period (week 3 onward). Third, it was defined as starting at the time when the woman would first be able to become aware of her pregnancy, that is, at the time when her menstruation failed to appear, on average approximately 4 weeks after the last menstrual period (week 5 onward).
Study population
Of the 478 women invited to participate in the study, 439 were interviewed. A total of 394 had answered the relevant questions on binge drinking in the questionnaire. Participants did not differ from nonparticipants with respect to age, prepregnant body mass index, the average alcohol intake per week during pregnancy, employment, parity, gestational age at birth, or the birth weight of the child. A total of 371 women for whom information was available for both instruments were included in this study. These women did not differ from the 68 women who were interviewed but did not answer the questionnaire with respect to the above variables.
Statistics
The proportion of "binge drinkers in pregnancy" was calculated using the above definitions, and the agreement between the two methods was assessed by the percentage of agreement and kappa (19
).
For all analyses, women contributed information on binge drinking only for gestational weeks for which information was available from both the questionnaire and the interview.
The study was approved by the regional ethics committee and the Danish Data Protection Agency.
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RESULTS
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Characteristics of the participants may be seen in table 2. The proportion of women who reported binge drinking in early pregnancy depended on the number of weeks that were included in the definition of pregnancy. If pregnancy was defined as starting on the first day of the last menstrual period, 48 percent of the women reported
1 episode of binge drinking in the interview compared with 42 percent in the questionnaire. If pregnancy was defined as starting at the time of conception, the percentages were 38 and 31, respectively. If it was defined as the time when the woman would be able to become aware of her pregnancy, the percentages were 13 and 11, respectively (table 3). The agreement between the two methods ranged between 81 percent and 86 percent, and the agreement as measured by kappa values was moderate to good (table 3).
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TABLE 2. Characteristics of participants (n = 371) (pregnant women attending routine antenatal care), Aarhus, Denmark, 1998
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TABLE 3. Agreement between two measures of binge drinking ( 5 drinks on a single occasion) during pregnancy: personal interview versus questionnaire, Aarhus, Denmark, 1998*
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Similarly, the number of binge episodes reported depended very much on the number of weeks included in the definition of pregnancy (figure 1).

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FIGURE 1. Percentage of women reporting one or more episodes of binge drinking during the first 20 weeks of pregnancy, among women who reported binge drinking in interview, Aarhus, Denmark, 1998. The time of binge drinking was measured from the first day of the last menstrual period.
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Independent of the method, the proportion of women reporting
1 binge episode peaked in week 3 (22.9 percent in the interview compared with 17.8 percent in the questionnaire) and thereafter declined steadily to reach 1.41.7 percent in week 7 (figure 2).

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FIGURE 2. Percentage of women (n = 371) reporting one or more episodes of binge drinking during each of the first 20 weeks of pregnancy, Aarhus, Denmark, 1998. The percentage was calculated for each week, and the gestational age was calculated from the last menstrual period.
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DISCUSSION
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It is likely that the specific effect of alcohol on the fetus depends on the gestational age at the time of alcohol intake. The fetus is most susceptible to the teratogenic effects of alcohol (or any other teratogenic substance) during organogenesis in the first trimester. Human studies have suggested that alcohol may increase the risk of spontaneous abortion in the first trimester but not in the second (20
, 21
), and we have recently shown that alcohol intake in the third trimester seems to be of far more importance in relation to preterm delivery than intake in the second trimester (22
). If the adverse effects of alcohol intake are unique to the period of intake, timing becomes an important aspect, particularly in relation to binge drinking.
Previous studies of the effects of binge drinking in pregnancy have asked about binge drinking in very different ways. Most studies defined binge drinking as intake of
5 drinks on a single occasion or a single day (11
, 12
, 15
17
) or the equivalent amount in ounces (13
). Only one study used a different definition (4045 g of absolute alcohol on a single day, the equivalent of approximately four standard drinks) (14
). Although it has been suggested that the number of binge episodes may be of importance (16
), only three studies seem to have asked about the number of binge episodes (13
, 14
, 16
). Most studies seem to have asked about binge drinking in pregnancy in general without specifying how they defined the beginning of pregnancy (13
, 15
17
). Passaro et al. (14
) specifically asked about the number of binging days during the month before filling in the study questionnaire at 1823 weeks of gestation, and Streissguth et al. (11
, 12
) specifically asked about alcohol consumption after recognition of pregnancy.
This may explain why almost all studies have found no or very little effect of binge drinking on adverse pregnancy outcomes. For studies of malformations, the data used may have covered the period of susceptibility (16
, 17
), but any potential association might have been overlooked because the analyses included all the binge episodes reported. For birth weight (13
15
), length at birth (13
, 15
), head circumference (13
), gestational age (13
), and the Apgar score (13
), the data used have probably not covered the main period of susceptibility in late pregnancy, except perhaps for the study by Godel et al. (15
). Only the two studies (based on the same cohort) that did find an association between binge drinking and learning disabilities and other long-term effects specifically distinguished between binge drinking before and after recognition of pregnancy (11
, 12
).
This study demonstrates that the frequency of binge drinking changes dramatically during the first few weeks of pregnancy, and from week 7 onward binge drinking is a rare event. Any overall measure of binge drinking that does not involve timing will thus be highly dependent on the women's definition of pregnancy. Some will recall only the time when they knew they were pregnant, some will think in terms of biology and define their pregnancy as starting at conception and, because all women are asked about their last menstrual period, some will probably define pregnancy as starting at this point in time. Information obtained on overall episodes of "binge drinking in pregnancy" will therefore cover different time periods with very different frequencies of binge drinking (figure 2). Even if the period of susceptibility is covered by the data and even if the period of susceptibility for the outcome under study includes the early weeks of gestation (e.g., spontaneous abortions or malformations of the heart), the associations found will be obscured by the mixture of the definitions of pregnancy and weakened by the information on binge drinking outside the period of susceptibility.
When questions on the same issue are asked repeatedly with intervals of a few weeks, it is possible that the women become more aware of their drinking behavior. If this were to affect the intake level reported, one would expect the women to report a lower intake level at the second point in time. Yet, the women reported a slightly higher proportion of binge episodes in the interviews compared with the questionnaires, particularly because of a higher proportion of binge episodes during the first few weeks after conception. The decrease in kappa values across table 1 despite a consistently high percentage of agreement may be explained by the increasingly unbalanced marginal totals across the table (23
). Differences were in any case small, and both methods yielded similar patterns of intake.
It has been suggested that self-administered questionnaires may yield higher estimates of alcohol intake compared with interviews, because a self-administered questionnaire requires no verbal or nonverbal justification for the answers given (24
). Information from interviews, on the other hand, might tend to cluster around socially acceptable norms because of an interviewer effect (24
). Two previous studies that compared prospective information on alcohol intake in pregnancy obtained from questionnaires and interviews (prospective in relation to pregnancy outcome) have failed to confirm these suggestions (21
, 24
).
It has been suggested that the respondent's rapport with the interviewer and the extent of confidentiality implied in the procedure are important aspects in an interview situation (25
). Neither substantial nor systematic differences were seen between the interviewers with respect to any of the measures reported here.
During the interviews, only three women (0.8 percent) did not remember whether they had had any binge episodes, and three women who reported 12 binge episodes did not remember when. Thus, 98 percent of the women interviewed were able to give accurate information on the number of binge episodes as well as the timing. For the questionnaire, this was the case for 95 percent of the women. This difference, although small, may be due to the women's making a special effort to remember previous binge episodes when confronted with an interviewer. It was reported by the interviewers that only very few women appeared uncertain of the accuracy of the information given. This suggests that it is possible with two simple questions to obtain the relevant information on the number of binge episodes as well as the specific weeks when binging took place.
Gestational age was calculated from the last menstrual period adjusted for cycle length, or it was based on the best available clinical judgment at the time of the interview. These estimates were used, because they were the ones available when the information was obtained and, therefore, the estimates referred to by the women when trying to recall their binge episodes. For 290 of the 371 women, an early, ultrasonographically determined, biparietal diameter measured before 20 completed weeks of gestation was subsequently available. Recalculation of the gestational age at interview using this information resulted in a mean difference between the two measures (last menstrual period measure ultrasound measure) of -0.3 week (10/90 percentiles = -1.4/0.8 weeks).
To obtain valid results, future research into the adverse effects of binge drinking in pregnancy should take into account the number of binge episodes as well as the time of binge drinking. This information may easily be obtained from most pregnant women by asking two questions in interviews or questionnaires.
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ACKNOWLEDGMENTS
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This study was supported by the Faculty of Health Sciences, University of Aarhus, Aarhus, Denmark.
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NOTES
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From the Perinatal Epidemiological Research Unit, Department of Obstetrics and Gynaecology, Aarhus University Hospital, Skejby Sygehus, 8200 Aarhus N, Denmark (e-mail: skejuk{at}au.dk) (reprint requests to U. Kesmodel at this address).
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Received for publication November 20, 2000.
Accepted for publication April 4, 2001.