1 Danish Epidemiology Science Centre at the Department of Epidemiology Research, Statens Serum Institut, 5, Artillerivej, DK-2300 Copenhagen S, 2 Department of Social Medicine, Department of Public Health, University of Copenhagen, 3, Blegdamsvej, DK-2200 Copenhagen N, 3 Danish Epidemiology Science Centre at the Institute of Preventive Medicine, Copenhagen Hospital Corporation, Kommunehospitalet, DK-1399 Copenhagen K and 4 Danish Epidemiology Science Centre at the Department of Epidemiology and Social Medicine, 6, Vennelyst Boulevard, DK-8000 Aarhus C, Denmark
![]() |
Abstract |
---|
![]() ![]() ![]() ![]() ![]() ![]() ![]() ![]() |
---|
Key words: alcohol/birth cohort/fecundity/time to pregnancy
![]() |
Introduction |
---|
![]() ![]() ![]() ![]() ![]() ![]() ![]() ![]() |
---|
In a recent follow-up study a >50% reduction in fecundity was found in women with any alcohol intake compared with non-drinkers (Jensen et al., 1998). These results, if true, call for substantial modifications of our alcohol policy for women trying to become pregnant. The results, though, were based upon a small study with highly selected participants.
This study aims to examine the association between female consumption of alcohol and waiting time to pregnancy, with particular focus on moderate levels of alcohol intake. The size of the study enables us to examine whether a potential association is modified by body mass index (BMI), smoking and parity.
![]() |
Materials and methods |
---|
![]() ![]() ![]() ![]() ![]() ![]() ![]() ![]() |
---|
The study included 39 612 women, recruited from October 1, 1997, to March 15, 2000, who had given their first pregnancy telephone interview and who were still pregnant at that time.
Measurement of exposure and potential confounders
The participants were asked about their drinking habits before pregnancy, specified for each type of beverage; beer, wine and spirits. The question was: How many ordinary beers did you drink per week before you became pregnant? and the same question was asked for glasses of wine and glasses of spirits. One bottle of beer contains 11.6 g of alcohol, and 12 g of alcohol is an approximate average for one serving of wine or spirits in Denmark. In the analysis we added each type of beverage to one variable of total alcohol consumption per week. If some alcohol intake was reported, but less than one unit per week, this was coded as half a unit per week. Low, moderate and high alcohol intake was defined according to the following levels; 0.52 drinks per week, 2.514 drinks per week and >14 drinks per week respectively. Most women reported drinking 0.52 drinks per week, and this group was therefore used as the reference exposure.
Since no information about smoking habits before pregnancy was available, we used the question whether they had smoked at any time in the first trimester to categorize participants as either smokers or non-smokers.
BMI was calculated as weight in kg/height in m2, on the basis of the women's report on height and weight before pregnancy.
Measurement of outcome
The outcome measure was waiting time to pregnancy based upon the following question: How long a time did you try to become pregnant, before you succeeded? followed by fixed answering categories: 02 months, 35 months, 612 months and >12 months. The women were also asked whether the pregnancy was planned, partly planned or not planned. If the pregnancy was unplanned they were not asked about waiting time to pregnancy. Subfecundity is, in this study, defined at two different levels; namely having a waiting to pregnancy of >5 and >12 months.
Statistical analysis
The association between alcohol intake and waiting time to pregnancy was estimated at two levels for waiting time to pregnancy (>5 and >12 months) by means of standard logistic regression (Olsen et al., 1998). Since results were similar at the two cut-off levels, we combined the results by using the method of Kalbfleisch and Prentice (Kalbfleisch and Prentice, 1980
). We used a logistic model to estimate the conditional probability of not being pregnant within each waiting time interval given that the woman did not become pregnant in the previous intervals. Alcohol intake, potential confounders such as age, parity, smoking, thinness (BMI <18 kg/m2) and obesity (BMI >30 kg/m2), and a categorical variable to indicate the waiting time interval were included in the model as explanatory variables. Analyses were done in SPSS 9.0.
All effect measures are given in subfecundity odds ratios (OR) where a high OR indicates a longer waiting time.
![]() |
Results |
---|
![]() ![]() ![]() ![]() ![]() ![]() ![]() ![]() |
---|
Almost half of the women had obtained their pregnancy within the first 2 months, but 15% waited more than a year to become pregnant. Most women (79%) reported an alcohol intake of 0.57 drinks per week (Table I). Twelve percent reported no intake at all and 1% reported a high intake. Women in the highest alcohol group reported on average 18 drinks per week, and 54 women reported an intake of more than 21 drinks per week.
|
|
|
|
|
|
![]() |
Discussion |
---|
![]() ![]() ![]() ![]() ![]() ![]() ![]() ![]() |
---|
The most consistent finding was a longer waiting time to pregnancy in women who reported no alcohol intake. We found no support for the findings of two recent studies suggesting that low levels of alcohol were associated with reduced fecundity (Hakim et al., 1998; Jensen et al., 1998
).
All epidemiological studies on alcohol intake, including our study, rely on self-reported data, which are expected to be under-reported. If this under-reporting is of similar magnitude at all levels of exposure, our results would indicate no effect at even higher levels of intake. If, on the other hand, heavy drinkers were more likely to deny their intake, waiting times could be longer for the reported non-drinkers, as we found. We expect this problem to be small since very few, if any, alcohol abusers were recruited to the study.
We assume to have recruited about 60% of those invited. This response rate could cause selection bias if the decision to participate is associated with both alcohol intake and waiting time to pregnancy. We believe this is unlikely, since studying determinants of subfecundity was not specified as one of the aims of the cohort. Furthermore, we studied an alcohol effect at intake, which is considered acceptable in Denmark.
This study includes only women who actually became pregnant and all effect measures are conditional upon having obtained a pregnancy that survived at least the first 12 weeks of gestation.
Only data on women who planned their pregnancies are presented in this paper. If women with a high alcohol intake practice pregnancy planning less often we would expect risk estimates to be biased towards high values, which was not seen. Furthermore, including women with partly planned pregnancies did not have much influence on any of the effect measures.
Bias caused by past reproductive experience is an often neglected problem (Olsen, 1999). If women with previous long waiting times unrelated to alcohol intake reduce their drinking habits when they try to become pregnant again, women with a low alcohol intake would have long waiting times to pregnancy. We found the opposite. Even when we restricted the analyses to nulliparous women, who have less reproductive experience to modify their behaviour, no association was found between alcohol intake and waiting time to pregnancy.
Studying determinants of subfecundity requires comparable persistence in pursuing a pregnancy attempt among the compared groups (Basso et al., 2000). We expect this problem to be of minor importance after correction for age and parity.
We found smoking and BMI to be associated with subfecundity, which is consistent with previous findings (Olsen et al., 1983; Joffe and Li, 1985
; Joesoef, 1993
; Zaadstra et al., 1994
; Curtis, 1997
; Bolumar et al., 2000
).
Throughout our analysis non-drinkers had a consistently higher risk of subfecundity than women with some alcohol consumption. We do not expect alcohol to improve fecundity but a moderate intake may correlate with a higher frequency of intercourse, which may explain the longer waiting times in women who reported no intake. Data on frequency of intercourse were not available.
Misclassification on the proper time of exposure may partly explain our results (Weinberg et al., 1994). We asked for average alcohol intake before pregnancy without specifying the time period, but we assume that women with shorter waiting times more often report alcohol use closer to starting time of pregnancy planning than women who waited longer to become pregnant. If women with longer waiting times reduced their alcohol intake to no intake during the planning period, believing that this would increase their chances of becoming pregnant, we would expect the high risks we see for non-drinkers. If women with past fecundity problems totally abstain from drinking alcohol when again trying to become pregnant, this could also explain our findings of longer waiting times among non-drinkers. We do not believe, however, that these methodological problems are important at present, since alcohol is not known to depress female fecundity in general in Denmark.
The study showed shorter waiting times for those with a low intake of alcohol compared with non-drinkers. Smaller amounts of alcohol may have a positive impact on the female reproductive system, perhaps by providing some stress control (Negro-Vilar, 1993; Wasser et al., 1993
; Sanders and Bruce, 1997
; Hjollund et al., 1999
).
In conclusion our findings suggest that moderate alcohol intake is not strongly associated with subfecundity.
![]() |
Acknowledgements |
---|
![]() ![]() ![]() ![]() ![]() ![]() ![]() ![]() |
---|
![]() |
Notes |
---|
![]() |
References |
---|
![]() ![]() ![]() ![]() ![]() ![]() ![]() ![]() |
---|
Bolumar, F., Olsen, J., Rebagliato, M. et al. (2000) Body Mass Index and Delayed Conception: A European Multicenter Study on Infertility and Subfecundity. Am. J. Epidemiol., 151, 10721079.[Abstract]
Curtis, K.M. (1997) Effects of cigarette smoking, caffeine consumption, and alcohol intake on fecundability. Am. J. Epidemiol., 146, 3241.[Abstract]
Florack, E.I., Zielhuis, G.A. and Rolland, R. (1994) Cigarette smoking, alcohol consumption, and caffeine intake and fecundability. Prev. Med., 23, 175180.[ISI][Medline]
Grodstein, F., Goldman, M.B. and Cramer, D.W. (1994) Infertility in women and moderate alcohol use [see comments]. Am. J.Public Health, 84, 14291432.[Abstract]
Hakim, R.B., Gray, R.H. and Zacur, H. (1998) Alcohol and caffeine consumption and decreased fertility [published erratum appears in Fertil. Steril., 1999, 71, 974]. Fertil. Steril., 70, 632637.[ISI][Medline]
Hjollund, N.H., Jensen, T.K., Bonde, J.P. et al. (1999) Distress and reduced fertility: a follow-up study of first-pregnancy planners. Fertil. Steril., 72, 4753.[ISI][Medline]
Jensen, T.K., Hjollund, N.H., Henriksen, T.B. et al. (1998) Does moderate alcohol consumption affect fertility? Follow up study among couples planning first pregnancy [see comments]. Br. Med. J., 317, 505510.
Joesoef, M.R. (1993) Fertility and use of cigarette, alcohol, marijuanen, and cocaine. Ann. Epidemiol, 3, 592594.[Medline]
Joffe, M. and Li, Z. (1985) Male and Female Factors in Fertility. Am. J. Epidemiol., 140, 921929.[Abstract]
Kalbfleisch, J.D. and Prentice, R.L. (1980) Discrete Failure Time Models, an Alternative Discrete Model. In The Statistical Analysis of Failure Time Data. John Wiley and Sons, pp. 3738.
Negro-Vilar, A. (1993) Stress and other environmental factors affecting fertility in men and women: overview. Environ. Health Perspect, 101, 5964.
Olsen, J. (1999) Design options and sources of bias in time-to-pregnancy studies. Scand J. Work Environ Health, 25, 57.[ISI][Medline]
Olsen, J., Rachootin, P., Schiøtt, A.V. et al. (1983) Tobacco Use, Alcohol Consumption and Infertility. Int. J. Epidemiol., 12, 179184.[Abstract]
Olsen, J., Bolumar, F., Bisanti, L. et al. (1997) Does Moderate Alcohol Intake Reduce Fecundability? Alcohol Clin. Exp. Res, 21, 206212.[ISI][Medline]
Olsen, J., Juul, S., and Basso, O. (1998) Measuring time to pregnancy. Hum. Reprod., 13,17511756.
Sanders, K.A. and Bruce, N.W. (1997) A prospective study of psychosocial stress and fertility in women. Hum. Reprod., 12,23242329.[Abstract]
Wasser, S.K., Sewall, G. and Soules, M.R. (1993) Psychosocial stress as a cause of infertility. Fertil. Steril., 59, 685689.[ISI][Medline]
Weinberg, C.R., Baird, D.D. and Wilcox, A.J. (1994) Sources of bias in studies of time to pregnancy. Statistics in Medicine, 13, 671681.[ISI][Medline]
Zaadstra, B.M., Looman, C.W., te Velde, E.R. et al. (1994) Moderate drinking: no impact on female fecundity. Fertil. Steril., 62, 948954.[ISI][Medline]
Submitted on May 4, 2001; accepted on September 6, 2001.