Use of benzodiazepine (BZD) drugs or hypnotic benzodiazepine receptor agonists (HBRAs) during pregnancy may represent a hazard for the foetus. In order to analyse this in an adequate way, knowledge of maternal characteristics as putative confounders is needed.
In the Swedish Medical Birth Register, 2149 pregnant women using BZDs or HBRAs were identified, 1944 of them in early pregnancy. These women were compared with other women (n = 859 455) giving births during the same period (1 July 1995–31 December 2004). The following maternal characteristics were studied: age, parity, smoking habits, education, previous miscarriages, years of involuntary childlessness as an estimate of subfertility, concomitant drug use and some pregnancy complications.
Use and/or reporting of BZDs or HBRAs increased with maternal age. It was higher at first and 4+ parity and increased markedly with maternal smoking. Women with low education reported a higher use than women with high education. Previous miscarriage or subfertility had little impact on the use of these drugs. Preterm birth and caesarean section (also at term birth) were more common than expected. In women using BZDs or HBRAs, other types of psychoactive drugs were used in excess.
Women using BZDs or HBRAs differ in many aspects from women not using those drugs. These differences may act as confounders in the analysis of pregnancy outcome. Copyright © 2007 John Wiley & Sons, Ltd.