A retrospective cohort study was carried out using the electronic booking records of women with singleton pregnancies who delivered in a large Dublin maternity hospital between 2000 and 2007. The data from the booking interview was linked to the electronic delivery record and neonatal records with information on the infant up until first hospital discharge. Information on peri-conceptional alcohol consumption (prior to pregnancy and up until the pregnancy was confirmed) was recorded electronically using a computerised antenatal questionnaire administered by trained midwives at the patient's first antenatal visit, which usually occurred at about 12 weeks' gestation. Women were asked two questions at the time of booking; 1) whether they drink alcohol and 2) how many units of alcohol they drink per week. Women who described themselves as complete abstainers from alcohol were described as "never" drinkers. For women who reported drinking alcohol, levels of consumption were recorded in the following bands: 0-5 units per week (this group included very occasional drinkers who may have had no alcohol intake some weeks but did drink on occasions), 6-11 units per week, 11-20 units per week and >20 units per week. For the analyses subjects were divided into four groups: never drinkers, drinkers consuming 0-5 units per week (similar to the NICE recommendation for occasional alcohol intake and termed low alcohol intake), drinkers consuming 6-20 units per week (in excess of the NICE recommendation and termed moderate alcohol intake) and drinkers consuming greater than 20 units per week (excessive alcohol intake for women and termed high alcohol intake).
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 and 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.
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 special care baby 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), genetic testing and neonatal death. Every woman had an ultrasound scan at the booking antenatal visit. 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. 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. Small for gestational age was defined as a birth weight less than the 10th percentile using individualised birth rate ratios (corrected for maternal height and weight, parity, infant sex, ethnicity and gestation) http://www.gestation.net. Stillbirth was defined as delivery of a baby showing no signs of life at or after 24 weeks gestation.
The analyses were performed using the Statistical Package for Social Sciences (SPSS version 15). Descriptive statistics were used to characterise the study subjects by category of alcohol intake. Comparisons were made between the different alcohol intake groups to identify socio-demographic predictors of peri-conceptional alcohol intake. Logistic regression analyses were performed to measure the association between alcohol exposure and adverse perinatal outcomes. The "never" 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 comparisons were made adjusting for potential confounding factors including maternal age, single marital status, socio-economic status, nationality, private health insurance, nulliparity, unplanned pregnancy, late booking, smoking, and illicit drug use. These factors were chosen because of their known or possible association with perinatal outcome. Results are reported as proportions, odds ratios (OR) and 95% confidence intervals (CI).
The study received the approval of the Coombe Women and Infants University Hospital's research ethics committee: Study No. 22-2009.