from PART III - ASSISTED REPRODUCTION
Published online by Cambridge University Press: 04 August 2010
INTRODUCTION
Human reproduction is an inefficient process. It is estimated that approximately one-fifth of conceptions result in life birth (1, 2). During the past three decades, substantial progress has been achieved in improving stimulation protocols and fertilization procedures. In the same period, however, there was only minimal advancement embryo implantation and pregnancy rate per embryo transfer (3). The average birthrate per complete cycle of in vitro fertilization (IVF) still ranges from 29.9 to 43.7 percent per egg retrieval (4).
It has been estimated that 30 percent of embryos are lost in the preimplantation phase, and 30 percent are lost after the embryo is implanted in the uterus (5). It has been suggested that unsuccessful implantation is attributed to abnormal embryo karyotype (6). Data from genetic studies, however, indicate that the overall prevalence of karyotype abnormalities among preimplantation embryos ranges from 50 to 60 percent (7, 8). Based on these data, the expected implantation rate would be much higher than currently observed (9). This discrepancy suggests that implantation failure could be the result of abnormalities in the mother (6).
Recent evidence suggest that abnormalities such as thyroid anomalies, increased levels of circulating natural killer cells (10, 12), the presence of mouse embryo assay factor (13, 14), and inherited and acquired thrombophilia may contribute to the failure of implantation (15).
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