Unexpected heaping in reported gestational age for women undergoing medical abortion

In August 2006, the Planned Parenthood Federation of America (Planned Parenthood) conducted an extensive audit of first-trimester medical abortions with oral mifepristone plus buccal misoprostol through 56 days of gestation so that patients could be given accurate information about the success rate of the new regimen.

We sought to evaluate the effectiveness of this buccal misoprostol regimen and to examine correlates of its success during routine service delivery.

Audits in 10 large urban service points were conducted in 2006 to estimate the success rates of the buccal regimen. Success was defined as medical abortion without vacuum aspiration.

We discovered unexpected heaping of reported gestational age (GA) on days divisible by 7.

Such heaping, which has not been reported in the literature, would make it more difficult to detect a modest trend in declining effectiveness with increasing GA, if there were one. High coefficients of variation of sac size and crown-rump length characterize the early gestational weeks. We suspect, but are unable to prove, that the source of the heaping found in our investigation is a tendency for operators of ultrasound machines at some sites to simplify reporting by rounding a portion of the results to a date corresponding to the nearest complete gestational week. We believe that immediate supervisory awareness and feedback may reduce the extent of the problem. However, the problem may persist in multiple-site studies given the underlying variability of ultrasound measurements with differently calibrated machines and different rules for recording data, some of which may permit acceptance of an estimate based on the stated date of the last menses, if it differs by no more than 2 or 3 days from the ultrasound result.