Drinking alcohol in pregnancy can cause a wide range of neurodevelopmental and other harms to the embryo/foetus and is a leading, but preventable, cause of birth defects, with lifelong implications (1). Globally, the estimated prevalence of Fetal Alcohol Spectrum Disorders (FASD) is 7.7 per 1000 in the general population, with the highest prevalence in the European Region at 19.8 per 1000 (2). FASD is associated with a wide range of comorbidities (3), resulting in high costs for both children and adults (4). Appropriate prevention responses are therefore a public health priority. The World Health Organization recommends that health professionals ask all women about their alcohol use when they attend antenatal care (5), however many women under-report their consumption (6) and it can be difficult for midwives to identify those at risk (7). A recent UK study which tested samples of meconium for alcohol biomarkers found at least a five-times higher prevalence of in-pregnancy drinking than with self-report data from the same women (8). Improved screening methods are needed to identity those at risk and maximise maternal and child health.
A recognized challenge to research on alcohol consumption in pregnancy, is that women who consent to take part in studies may not be representative of the wider population. Drinking alcohol in pregnancy is highly stigmatized in the UK and many other cultures, and pregnant women who are drinking may feel ashamed or defensive (9). Furthermore, women report a fear of judgmental attitudes (10) or repercussions for them as parents including intervention by child protection services (11). Women drinking in pregnancy may therefore be least likely to take part in a study of this topic. This problem has hampered the development of accurate screening methods for drinking in pregnancy, as it has not been possible to identify a gold standard or ‘true positive’ measure of alcohol consumption in pregnancy – against which any new methods could be compared or which could be used to study the effectiveness of interventions to prevent or reduce such consumption (12, 13). Other studies of alcohol consumption have faced similar challenges, whereby members of the group of interest are more likely to decline to take part in the study, biasing the sample (14).
The Alcohol and Child Development Study (ACDS) involves a cohort of pregnant women in a UK city, and aims to inform the development of improved methods of identification of women at risk of having a child affected by foetal alcohol exposure. The study will anonymously follow the children of a cohort of women identified in pregnancy, to examine whether or not there is a relationship between either positive maternal blood tests for alcohol biomarkers and/or self-reported alcohol consumption in pregnancy, and later childhood developmental disorders. If women drinking in pregnancy opted out of the cohort, such as for the reasons described above, the ACDS would be unable to achieve its aims.
Approximately 2ml of extra blood was collected from pregnant women for the ACDS, at the same time as a routine antenatal blood sample, at about 14 weeks of pregnancy, except in those who opted out of the study. All women received a study information sheet informing them of the extra sample in general terms. Neither the women nor their midwives, were made aware of the testing of the samples for a biomarker of alcohol consumption or the anonymous follow up of the cohort for childhood developmental disorders. Also after discussion with senior midwifery staff, the location of the study is anonymized in this report.
It is important for the ACDS, as well as for future studies of screening for alcohol consumption or other stigmatized behaviour in pregnancy, and any future studies taking a similar approach to consent, to examine whether the procedures adopted resulted in a representative cohort. In other words, did this method of consent appear to succeed in eliminating the bias as intended and did it introduce any other form of bias, whereby women with certain demographic characteristics were more likely to have not had the sample taken, if they opted out?
The aim of this paper therefore, is to describe the extent to which the women who gave a blood sample in the ACDS were representative of the wider population of women attending the relevant antenatal ‘booking’ appointments in the study city from 12th June 2017 to 30th June 2018 in terms of routinely collected data at the first maternity visit.