Monitoring data and safety in the WHO Antenatal Care Trial

A committee to monitor data and safety in a large clinical trial should have members with expertise in biostatistics, epidemiology and the clinical field relevant to the trial. Its mandate should cover both logistics and the safety of study subjects, issues which to some extent overlap. While a steering committee and field staff members ideally should be blinded to the experimental and control arms of a randomised clinical trial, the data and safety monitoring committee (DSMC) should have full access to interim trial data to fulfil its role as watchdog. One initial question to be resolved concerns if and when to advise stopping a trial because of danger to study subjects, or on the other hand obvious benefits, in one trial arm. The DSMC of the WHO Antenatal Care Trial decided not to establish any definite stopping rules before implementation. After a scrutiny of the adopted procedures for data collection and handling, the DSMC received monthly reports of recruitment, and individual summary reports of three adverse events by site and trial arm: maternal deaths, fetal deaths and cases of eclampsia. At the time of writing (December 1997) recruitment to the trial is almost complete, but data collection will continue throughout most of 1998, until every index pregnancy has ended in birth or miscarriage. So far, the balance of untoward events between the intervention and control arms have not given cause for alarm.