Background
Many women continue to consume alcohol in pregnancy despite recommendations that they should abstain from alcohol in order to minimise potential risks to the fetus. The advice from the Department of Health in Ireland and the United Kingdom is that alcohol should be avoided during pregnancy. This is similar to the advice by the Surgeon General in the United States that pregnant women or women who may become pregnant should abstain from alcohol. However, the National Institute for Health and Clinical Excellence (NICE) in the United Kingdom recommends that women should be advised to drink no more than one to two units once or twice a week [
1]. This conflicting information is likely to be confusing for women who may wish to continue "social" drinking in pregnancy.
A recent Australian study reported that only 41% of pregnant women abstained from alcohol throughout each trimester [
2]. An Irish study reported that 81% of women drink alcohol in the peri-conceptional period. However it was not possible to differentiate clearly between pre-pregnancy alcohol use and continuing alcohol use once pregnancy is confirmed [
3]. In the Southampton Women’s Survey 70% of women continued to drink in early pregnancy with 10% of drinkers consuming more than four units of alcohol per week [
4]. In a Swedish study, 12% of women reported continued alcohol consumption in pregnancy and 5% admitted binge drinking [
5]. Despite studies reporting high rates of alcohol use in pregnancy, ascertainment of the true prevalence and extent of alcohol consumption is difficult as under-reporting is common and women's understanding of what constitutes a standard "drink" or "unit" may differ from person to person. Similarly comparisons between different countries can be limited by differences in drinking patterns and different alcohol content of drinks and units [
6].
Various studies have associated moderate to heavy alcohol consumption with preterm birth, low birth weight and intrauterine growth restriction (IUGR) [
3,
7‐
9]. However, the results are often inconsistent and most studies have shown no significant associations when socio-demographic confounders are taken into consideration. [
6] Binge-drinking in pregnancy is also of concern, especially as this pattern of drinking has increased in the female population and is associated with unplanned pregnancy [
10,
11].
The aim of this study was to use a large cohort of women booking for antenatal care and delivering in a Dublin maternity hospital to investigate the behavioural changes reported in relation to alcohol use in pregnancy and whether there is an impact on adverse perinatal outcomes.
Methods
A prospective cohort study was carried out using the electronic booking records of women with singleton pregnancies who booked for antenatal care and delivered in a large Dublin maternity hospital between February 2010 and July 2011. The data from the booking interview were linked to the electronic delivery record and neonatal records with information on the infant up until first hospital discharge. Women who booked for antenatal care but delivered elsewhere were not included in the cohort (typically 1-2% of bookings each year).
One of the main objectives of this study was to record with accuracy the prevalence of alcohol consumption in the pre-conceptional period and during early pregnancy. The quality of the booking history was enhanced by use of a carefully structured questionnaire and a laminated drinks chart designed to record alcohol intake and pattern of use with greater accuracy (adapted from Royal College of Psychiatrists guidelines) [
12]. This guide to the alcohol content of named alcoholic beverages was made available to all midwives involved in booking patients for antenatal care. All women were asked the following questions at the time of booking (usually between 12 and 14 weeks):
2)
In the three months before this pregnancy how many units of alcohol did you drink each week?
3)
In the three months before this pregnancy how many times per month did you drink more than five units of alcohol on a single occasion?
4)
How much alcohol do you drink currently?
5)
Currently, how many times per month do you drink more than five units of alcohol on a single occasion?
The questions were found to be quick to administer and were acceptable to both patients and staff. Data from the first month was excluded to ensure that all staff had achieved competency with the new questionnaire and in ascertainment of alcohol units consumed. Women who described themselves as complete abstainers from alcohol were described as “non-drinkers”. For women who reported drinking alcohol, the exact number of units consumed per week was recorded. Binge drinking episodes, defined as more than five units of alcohol on a single occasion, were recorded as never, once a month and more than once a month. For the analyses subjects were divided into three groups: “non-drinkers”, “ex-drinkers”, and “current drinkers”. For sub-group comparisons current drinkers consuming 0–5 units per week were termed low alcohol intake. Current drinkers consuming 6–20 + units per week and drinkers reporting any episode of binge drinking during pregnancy were combined into an excess intake/binge category. Further sub-group analyses compared current drinkers who smoked with women who did not drink or smoke.
In addition to alcohol consumption, information on the following maternal characteristics was extracted from the electronic records: maternal age, marital status, socioeconomic group, nationality, public or privately funded antenatal care, parity, planned pregnancy, gestation at booking, smoking, illicit drug use, and referral to a social worker. Maternal age was divided into the following bands: < 20 years, 20–24 years, 25–29 years, 30–34 years, 35–39 years and > 40 years. Socioeconomic groups were classified as professional/manager/employer, home duties, non-manual, manual, unemployed and non-classifiable. Nationality was recorded as either Irish or non-Irish and further sub-divided by region into Western Europe, Asia/Middle East, Eastern Europe, Africa, South America, North America, Australia & New Zealand. Gestational age at booking was divided into < 12 weeks, 12–20 weeks and > 20 weeks. Smokers were defined as women who were current smokers at the time of attendance at their first antenatal visit. Illicit drug users were defined as women who had ever used illicit drugs.
Every woman had an ultrasound scan at the first antenatal visit and a further detailed structural anatomy scan at 20–22 weeks gestation. Gestational age was estimated from the calculation based on first day of the last menstrual period but the booking ultrasound scan estimate was preferred if the dates were uncertain or there was a discrepancy of more than seven days. Perinatal outcome measures included gestational age at delivery, live birth or stillbirth, birth weight, infant gender, infant’s condition at birth including Apgar scores at 1 and 5 minutes, admission to the neonatal unit, any suspected congenital abnormalities and whether resuscitation was required. Detailed data on the neonate were extracted on infants admitted to the neonatal unit including details on ventilation, suspected neonatal abnormalities including Fetal Alcohol Syndrome (FAS) and neonatal death.
Recorded congenital abnormalities were categorised according to the EUROCAT classification system (EUROCAT.
Instructions for the Registration and Surveillance of Congenital Anomalies. Belfast: European Surveillance of Congenital Anomalies Central Registry, 2009.) Preterm birth was defined as the birth of a live baby at less than 37 weeks gestation. Very preterm birth was defined as the birth of a live baby at less than 32 weeks gestation. Low birth weight was defined as weighing less than 2500 g and very low birth weight as less than 1000 g. Intrauterine growth restriction (IUGR) was defined as a birth weight less than the 10
th percentile using individualised birth rate ratios (corrected for maternal height and weight, parity, infant sex, ethnicity and gestation) (
http://www.gestation.net). Perinatal deaths included stillbirths or neonatal deaths. Stillbirth was defined as delivery of a baby showing no signs of life at or after 24 weeks gestation. Neonatal death was defined as the death of a baby in the first seven days of life. The perinatal death register, electronic delivery suite and neonatal unit records were used for ascertainment of stillbirths and neonatal deaths.
The analyses were performed using the Statistical Package for Social Sciences (SPSS version 16). Descriptive statistics were used to characterise the study subjects by category of alcohol intake. Comparisons were made between the three groups to identify socio-demographic factors associated with abstaining from alcohol or continuing to consume alcohol in pregnancy. Logistic regression analyses were performed to measure the association between alcohol exposure and adverse perinatal outcomes. The “non-drinker” category was chosen as the comparator for each of the analyses as this was unlikely to be biased by under-reporting and represented a group where we could be certain that there was no alcohol exposure in the peri-conceptional period, even for women with uncertain dates. Further stepwise logistic regression analyses were performed adjusting for potential confounding factors including maternal age, nationality, private health insurance, unplanned pregnancy, smoking, and illicit drug use. These factors were chosen because of their known or possible association with adverse perinatal outcome and because of baseline differences between the groups. Sub-group analyses compared women who consumed alcohol and smoked with women who did not drink or smoke. Results are reported as proportions, crude odds ratios (OR) and adjusted odds ratios (OR) with 95% confidence intervals (CI). All of the chosen variables for the logistic regression models are required data items on the computer system, therefore we did not have missing data as such, and the value "unknown" was rarely used. Binary logistic regression analyses with values coded as "unknown" resulted in a reduced sample size for the particular model but this did not influence the direction or magnitude of any of the associations.
The study received the approval of the Coombe Women and Infants University Hospital’s research ethics committee: Study No. 22–2009. Individual patient consent was not deemed necessary as the study analysed routinely collected data in an anonymised format.
Competing interests
The authors declare that they have no competing interests.
Authors’ contributions
DJM (guarantor) had the original idea for the study and, with all co-authors carried out the design. DJM and JB obtained funding. DJM, AM and BC were responsible for data cleaning. DJM carried out the analyses. DJM and AM drafted the manuscript which was revised by all authors. All authors read and approved the final manuscript.