On page 63 of the 5th edition of Does the Birth Control Pill Cause Abortions?, you mention a physician as stating that breastfeeding can cause abortions similar to hormonal contraception. You then quote a Dr. Hayes as stating that ovulation does not take place during breastfeeding, unlike the Pill, which can allow ovulation. I've come across some research done about 15 years ago that does document a fair number of ovulations during breastfeeding (see bottom of page). This research seems to indicate that in the few cycles immediately postpartum for a non-lactating mother and a few cycles when menstruation begins for a lactating mother, there is a possibility of an ovum being fertilized but not implanting due to inadequate corpus luteum. This is not direct evidence that breastfeeding prevents implantation of a zygote, but it is evidence that it could happen, probably with greater frequency than that with hormonal contraception.