Endocrinology of the peri-implantation period

Current research suggests that the appearance of endometrial integrins and pinopode appearance signal the opening of the receptive phase of the endome trium. These integrins may be activated by the interleukin-1 system (IL-l). IL-1 beta, expressed by the blastocyst, induces vascular endothelial growt h factor (VEGF) which, in turn, promotes angiogenesis and integrin expressi on in endometrial cells. The IL-l system also triggers the expression of ga mma interferon (IFN-gamma) from T lymphocytes. Decidual natural killer (NK) lymphocytes interact with invading trophoblast to generate leukaemia inhib itory factor (LIF). LIF induces uPA and gelatinase, enzymes which play a cr ucial role in trophoblastic invasion. Progesterone is a potent inhibitor of LIF, while oestrogen is a potent indu cer. Oestrogen in serum reflects follicular IL-I beta level and correlates with the outcome of embryo transfer after in vitro fertilization (IVF). Pro gesterone induces nitric oxide (NO) synthesis in the decidua, and NO promot es local vasodilatation and uterine quiescence Measurement of placental protein 14 (PP14, glycodelin-A) in serum may be of value as a screening test for implantation potential. However, human chori onic gonadotrophin (hCG) remains the most reliable predictor of successful implantation and pregnancy viability. An ovulation + 14 hCG level < 50 IU/l is often predictive of a non-viable outcome, while an ovulation + 21 hCG o f < 200 IU/l always indicates a non-viable pregnancy. hCG secretion by inva ding trophoblast appears to be negatively modulated by endothelin-I (ET-I) and prostaglandin F-2 alpha (PGF2 alpha), while tissue growth factors and c ollagenases are positive modulators of hCG expression. Pro alphaC, an inhibin pro-monomer, may have some value in monitoring corpu s luteum function. Inhibin A, activin A and follistatin all rises throughou t pregnancy and peak at 36 weeks of gestation. Relaxin is another ovarian h ormone that may have a role in predicting implantation. Relaxin induces pla cental protein 14 (PP14, glycodelin-A) expression in a receptive endometriu m, and measurement of serum PP14 may be of value as a screening test for im plantation potential.