Alcohol consumption and binge drinking in early pregnancy. A cross-sectional study with data from the Copenhagen Pregnancy Cohort

The fact that more than 70 % reported weekly alcohol consumption before pregnancy clearly illustrates that women generally do not comply with national guidelines. This percentage is actually lower than newly reported levels of weekly alcohol consumption among Danish women of fertile age [5], this in spite of the fact that since 2007 these guidelines have clearly recommended total alcohol abstinence while trying to conceive and during pregnancy. However, it is slightly lower than reported levels of 80 to 89 % found in neighboring Sweden as well as in Australia and New Zealand [27‐30]. The decline in weekly alcohol consumption during early pregnancy to 3 % in the Copenhagen Pregnancy Cohort is in accordance with contemporary literature, which also reports decreasing intake after confirmed pregnancy with a prevalence of approximately 5 % [23, 31].

While the proportion of women in the Copenhagen Pregnancy Cohort who engaged in one or more binge drinking episodes in 2012–13 was 35 %, another Danish study reported a prevalence of 22 % in early pregnancy with data from 2011 [23]. Data from a large regional cohort collected in the second largest city of Denmark (n = 56.545) in 2013 revealed that 40 % of the women included around gestational week 12 reported one or more episodes of binge drinking [5]. These different prevalences may be due to a diverse age distribution and socio-economic setting in the populations studied. Interestingly, the prevalence of binge drinking in early pregnancy presented in international literature ranges from 3 % to 55 % [22, 30‐32] but is for the most part lower than the Danish figures. These differing binge drinking levels may indicate that it is difficult to generalize between populations, and prevalence should be understood in the regional context of the respective study.

The general Danish population has one of the highest levels of alcohol consumption in Scandinavia [33] and alcohol is widely accepted and normalized in Denmark [34]. It is likely that lifestyle prior to conception is carried into pregnancy. Perhaps the relatively high Danish level of weekly alcohol consumption before pregnancy and binge drinking during early pregnancy reflect an influence of the national alcohol culture on pregnant women as well as on those contemplating pregnancy.

An Australian qualitative study supports this notion. In semi-structured interviews 12 women expressed the dilemma of not wanting to reveal an early pregnancy and at the same time engaging in social events that included alcohol consumption. Furthermore the study found that women lacked knowledge about the potential harmful effects of alcohol on the fetus [35]. Similarly, the social norm as well as a lack of knowledge may partly explain why women in the Copenhagen Pregnancy Cohort engage in alcohol consumption.

We have, along with previous research, investigated risk factors for binge drinking and non-compliance with general recommendations. Strandberg-Larsen et al. examined binge drinking in the early and unrecognized part of pregnancy and found this was more common among nulliparous women, age group 25–29 years and in those with higher degrees of education [4]. Our findings confirm these results with regards to parity, but not age and education. Furthermore our study along with others has established that smoking [31] and weekly alcohol consumption before pregnancy are strongly associated with continued drinking in early pregnancy [4, 22, 27, 36].

Another finding is that a lower degree of pregnancy planning is associated with binge drinking. This is in accordance with prior Danish results indicating that women with unintended pregnancies more often engage in binge drinking during early pregnancy than women with a very planned pregnancy [4, 23]. The association between a higher degree of pregnancy planning and lower rates of binge drinking is not unexpected given that compliance with overall guidelines before and during pregnancy is positively influenced by higher degree of pregnancy planning [23].

We also found that being pregnant after ART reduced the odds of binge drinking. Perhaps this is due to a higher level of knowledge about the effects of alcohol because of information given at the fertility clinic or because these pregnancies are very well planned and this group is highly motivated to change lifestyle in order to achieve pregnancy. To our knowledge no other studies have examined the association between pregnancy after ART and binge drinking.

Strengths of this study are the large sample size compared to previous studies [3, 29] and the fact that the hospital serves as a primary birth facility and is therefore representative for women in Denmark’s capital Copenhagen. This is largely due to the recruitment strategy of inviting women to participate when booking their first trimester nuchal translucency scan – a part of the routine Danish antenatal screening program. A further strength is the recentness of the data (2012–2013), which must be interpreted to reflect the current pattern of alcohol consumption. In addition our questionnaire was translated into English and as a result we included women not understanding Danish, which was 4 % in our study population. In earlier Danish studies [4, 37] good Danish speaking skills have often been inclusion criteria, which may have led to an underrepresentation of non-Danish speaking women. Although we made an effort to minimize recall bias by obtaining information on alcohol consumption early in pregnancy [38], we acknowledge that the risk of reporting bias is a potential limitation. It is plausible that pregnant women underreport alcohol habits [29, 38] and this may also be the case in our study. The missing data on binge drinking (n = 793) may be an indication that these questions are of a sensitive nature and subject to social-desirability bias [35, 39]. With regard to the key question on binge drinking, non-responders were characterized by having weekly alcohol consumption before pregnancy (p < 0.001) and a lower degree of planned pregnancy (p < 0.001) compared to those who answered the question. Given that weekly alcohol consumption and a lower degree of pregnancy planning were found to be associated with binge drinking this might have led to an underestimation of the prevalence of binge drinking. Furthermore, we are aware of the risk of underestimation of adjusted odds ratios for the associations between weekly alcohol consumption and pregnancy planning with binge drinking. It is difficult, however, to assess whether odds ratios for all other covariates could possibly be affected and whether this is leading to underestimation, overestimation or unchanging estimates.

In our study around 20 % did not respond the question about binge drinking. When the outcome is missing, there are generally no benefits in imputing the outcome, unless there is access to an auxiliary variable that is highly correlated with the outcome but not included in the multivariable model [40]. As we have included all important predictors in the multivariable model, we have no such extra variables that can be used in an imputation model. Actually, using imputed values of the dependent variable does not provide additional information but instead introduces additional error due to simulation error.

Though our questionnaire has been pilot-tested it can be discussed whether the lack of psychometric validation for the variable “degree of pregnancy planning” is a limitation in our study. Methods for measuring pregnancy planning have varied widely between studies and each has different merits and shortcomings [41]. Our finding that pregnancy planning is associated with binge drinking is in accordance with studies both by Backhausen et al. [23] and Tyden et al. [25]. Backhausen utilized the multi-itemed London Measure of Unplanned Pregnancies that has undergone validation [42].

The way of phrasing the questions should also be taken into consideration when describing drinking patterns of pregnant women. Furthermore, some studies have calculated separate rates for binge drinking before and after recognized pregnancy respectively [4, 22, 27]; we did not. Women in the Copenhagen Pregnancy Cohort were encouraged to recall the time before they knew of their pregnancy, but were not specifically asked to distinguish between the period before and after, respectively, of knowledge of their pregnancy. If women did indeed engage in binge episodes because they were unaware of their pregnancy as suggested in previous Danish studies [4, 5], this may be a potential limitation in our study. Such a distinction may be advantageous in future studies.

While there is no gold standard for collection of data on alcohol consumption, questionnaires and interviews have been found to provide comparable data [43]. A self-administered questionnaire, which was our choice, is acknowledged to be a good method for obtaining information on lifestyles related to less socially acceptable behaviors such as drinking and smoking [43].

The findings from our study may indicate a need for enhanced preconception care because of the marked differences between Danish national recommendations on alcohol abstinence in relation to conception and during early pregnancy and actual habits among women. The results emphasize that information should target not only pregnant women but also those intending pregnancy. This may have a positive effect on alcohol consumption in the unrecognized and early part of pregnancy. Furthermore, our study identified certain characteristics in pregnant women who engage in binge drinking and with this knowledge it is possible not only to design prevention strategies but also to target those women most at risk. Future clinical intervention studies are needed to examine the effect of such targeted prevention strategies in the preconception period on the rates of binge drinking.