Re-embarking in ART while still breastfeeding: an unresolved question.

Infertile women may request to embark on a new course of Assisted Reproductive Technologies (ART) in pursuit of a second child while still breastfeeding their first child. Breastfeeding is a time of profound hormonal changes that may interfere with ovarian physiology and uterine receptivity. Prolactin and oxytocin can mediate a plethora of potential detrimental effects. However, robust evidence to advise in favor or against ART during breastfeeding is lacking. In this narrative review, we reviewed the literature with the intent to shed light on this neglected issue. Possible adverse effects on ART success emerged for ovulatory mechanisms, folliculogenesis, uterine contractions, uterine peristalsis, and early embryo development. A negative impact of exogeneous hormones on infant health might be considered only for stimulation cycles. Overall, most concerns can be claimed for the clinical setting of ovarian stimulation, followed by the one of embryo transfer in a natural cycle and, finally, by the embryo transfer in a hormone replacement treatment preparation. However, in general, it seems wise to wait for breastfeeding to be discontinue before re-embarking on IVF, also considering that a too short interpregnancy interval may be deleterious to pregnancy outcomes. On the other hand, one must also recognize that available evidence is insufficient to deny access to treatments for women requesting earlier access. These women must be informed regarding the non-fully reassuring evidence.