Endocrine abnormalities in RPL

The process of implantation begins approximately 3 days after the embryo enters the uterus, between 19 and 23 days from last menstrual period. This period of high endometrial receptivity is known as the implantation window. After implantation has occurred, the maintenance of the pregnancy depends on a number of endocrine processes. The maternal endocrine system should create an environment that facilitates successful growth and development of the fetus. Hormones play a critical role in the expression, modulation, and inhibition of various growth factors, cytokines, cell adhesion molecules, and decidual proteins. Estradiol and progesterone control the orderly growth and differentiation of the endometrium for implantation of the embryo. A receptive endometrium is characterized by growth and coiling of spinal arteries, secretory changes in the glands, and decidualization of the stromal compartment. Failure of the endometrium to respond to these hormonal signals can result in defective placentation and an increased risk for miscarriage. It has been observed that the longer the ovulation-to-implantation interval, the higher the risk of early pregnancy loss. In this chapter, we discuss dysfunction of the endocrine system as one of the pathogenic mechanisms underlying recurrent pregnancy loss (RPL), accounting for up to 8-12 % of all pregnancy losses. This includes progesterone and luteal phase deficiency (LPD), hyperprolactinemia, polycystic ovary syndrome (PCOS), thyroid disease, and uncontrolled diabetes mellitus.