SUMMARY Prescription data for the three months before the last menstrual period and for the first trimester of pregnancy were obtained for 764 mothers whose children had a defect of the central nervous system and for an equal number of mothers of control babies born from the same doctors' practices. There was a statistically significant difference overall between the numbers of mothers who were prescribed drugs in the study and control groups during the trimester before the last menstrual period but no such difference was found for the first pregnancy trimester, nor was there a significant difference for any specific group of drugs. For a composite group of non-steroid anti-inflammatory drugs, salicylates, and sulphasalazine there was a significant difference for the trimester before the last menstrual period. There are arguments against such an artificial grouping, however, and when the individual drugs were considered the comparisons were no longer significant. The odds ratios for all medicines containing folic acid taken in the trimester before the last menstural period were considerably less than unity, in contrast with nearly all other comparisons. This supports a suggested protective effect against neural tube defects of folic acid supplements begun before the onset of pregnancy but the odds ratios of these comparisons were not statistically significant. The present study was designed to cover notifications of central nervous system defects for one year, 1981. A total of 1078 notifications of actual or suspected defects were sent to the Committee on Safety of Medicines (CSM) by the Office of Population Censuses and Surveys (OPCS). These study children were paired with control children and analysis of maternal drug histories in the trimester (three calendar months) before the last menstrual period as well as in the first trimester of pregnancy was undertaken. Patients and methodsThe method of selection of patients and the study procedures were similar to those of the previous investigations. Each malformed (study) child was paired with a normal liveborn child without a congenital abnormality from the same medical practice. The control child was the nearest normal birth in the practice within three months after the birth of the study child, and if such a child was not available then the last normal child born within the practice before the birth of the study child was taken, provided that the interval did not exceed 12 months.Method. Information on each study and control 1052 copyright.

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