Normal and abnormal implantation in spontaneous in-vivo and in-vitro human pregnancies

Abstract

Sheffield Fertility Centre, 26 Glen Road, Sheffield, S7 1RA, UK and University Department of Obstetrics and Gynaecology, Jessop Hospital for Women, Leavygreave Road, Sheffield, S3 7RE, UK Keywords: implantation; in-vitro fertilization; pregnancy; pregnancy loss; human chorionic gonadotrophin; human Introduction The endocrine characteristics of normal human pregnancy have been difficult to establish, chiefly because spontaneous pregnancies occur unpredictably. More reliable sources of early pregnancy data are conceptions following various assisted reproductive technologies although, unfortunately, many of these may not be useful for determining normal physiology, firstly, because there is multiple follicle development resulting from the use of exogenous gonadotrophins and, secondly, because human chorionic gonadotrophin (hCG) given to induce luteinization masks hCG from the implanting embryo. Furthermore, the practice, at least for in-vitro fertilization (IVF), of replacing up to 3 embryos renders assessment of the number of implantation sites uncertain. In-vitro fertilization in the natural or spontaneous cycle may provide