An update on hormonal regulation of early embryo-fallopian tube interactions: insights for improvements of assisted reproductive technology outcomes

Human fallopian tubes (FTs) play important roles in the whole reproductive process. FTs are the site for the final maturation of gametes, fertilization, transport of preimplantation embryos, and early embryonic development before entering the uterus. All these functions are critical in the establishment of a successful pregnancy. When the embryo is in transit through the FT, the FT microenvironment changes through endocrine, paracrine, autocrine, and juxtacrine mechanisms which involve various hormones and bioactive substances mainly from the neighboring cells. Therefore, the interactions between the embryo and the FT may be the earliest embryo-maternal communications that are essential for the establishment of pregnancy. This review critically discusses the evidence of various hormonal and bioactive mediated control of the microenvironment in the FTs during the earliest embryo-maternal communications. Moreover, we highlight existing gaps in the knowledge and the importance of exploring more of the physiology of FTs which will hold the key to producing high-quality embryos for patients seeking in vitrofertilization (IVF) treatments.