Thank you for publishing Dr Rank's report of an unintended pregnancy with a subdermal implant following a miscarriage.1 While I agree with much of Dr Melvin's response on behalf of the Clinical Effectiveness Unit,2 I think fundamentally the case highlights that continued reliance on apparent menstrual dates is flawed. Ultrasound dating of pregnancy has provided strong evidence that menstrual dates are frequently a poor guide to ovulation and conception timing. For this reason reliance on menstrual dates has …