There are protocols circulating the internet that suggest using antihistamines to assist with implantation with IVF and also to help avoid recurrent early pregnancy loss. Most have suggested using Claritin. New literature has shown the presence of Mast Cells (the histamine producing cells) are of importance and increase in quantity at the interface between the embryo and the mother's uterine lining. It seems that the release of histamine at the early stages of implantation is critical in allowing growth and invasion of the embryo (trophoblast) into the mother's uterine lining. Studies have shown that inhibition of this release may actually have a negative impact on this process.
Clearly patients that have been shown to have an excess of histamine production may benefit from some inhibition, but the excess should be a proven problem before generic use of antihistamines in IVF cycles. It does appear that over production (or lack of breakdown) of histamine later in the pregnancy (2nd and 3rd trimester) can be harmful and lead to IUGR and toxemia.