Naegele's rule revisited.

Recent literature suggests that Franz Carl Naegele's (1778-1851) rule for estimating the date of delivery has been misinterpreted, resulting in this being brought forward by five days. Baskett and Nagele's work underpinning this argument has become widely accepted and quoted in obstetrical and midwifery textbooks. However, our re-examination of Naegele's original statements does not support the recent findings. On the contrary, the original textbooks of Naegele clearly advise taking the first day of menstruation for the calculation of the date of delivery.