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The success of Assisted Reproductive Technology is critically dependent upon the use of well optimized protocols, based upon sound scientific reasoning, empirical observations and evidence of clinical efficacy. Recently, the treatment of infertility has experienced a revolution, with the routine adoption of increasingly specialized molecular biological techniques and advanced methods for the manipulation of gametes and embryos. This textbook – inspired by the postgraduate degree program at the University of Oxford – guides students through the multidisciplinary syllabus essential to ART laboratory practice, from basic culture techniques and micromanipulation to laboratory management and quality assurance, and from endocrinology to molecular biology and research methods. Written for all levels of IVF practitioners, reproductive biologists and technologists involved in human reproductive science, it can be used as a reference manual for all IVF labs and as a textbook by undergraduates, advanced students, scientists and professionals involved in gamete, embryo or stem cell biology.
The importance of aneuploidy in human reproductive failure
Human reproduction is a remarkably inefficient process. On average, fertile couples attempting to conceive only succeed in achieving a clinical pregnancy one month out of every five. For infertile patients undergoing in vitro fertilization (IVF) pregnancy rates are similarly low. More than 80% of the embryos transferred to the uterus during IVF treatment fail to implant and two-thirds of cycles do not produce a child . As a result, most IVF patients require two or more rounds of treatment to achieve a pregnancy. There are many potential reasons why an embryo might not establish a pregnancy; however, it is clear that one of the most important is chromosome abnormality. This is particularly true for embryos derived from women of advanced reproductive age. While it is not unusual for half of the blastocyst stage embryos produced by women in their early thirties to be chromosomally abnormal, this figure increases dramatically with age, such that an aneuploidy rate exceeding 75% is typical for blastocysts from women over the age of 40 . The high prevalence of aneuploidy, coupled with its detrimental impact on development, explains the majority of embryo implantation failures and miscarriages. Evidence for the lethality of aneuploidy comes from the detection of chromosome imbalances in the majority of miscarriages [3, 4] and from blinded studies where embryos, later revealed to be chromosomally abnormal, had been transferred to patients .
Cancer is more common after puberty during the reproductive life span of men and women, and many of the patients will be cured by combination treatment with surgery, chemotherapy and radiotherapy. The model of human ovarian reserve allows us to estimate the number of non-growing follicles (NGFs) present in the ovary at any given age, and it suggests that 81% of the variance in NGF populations is due to age alone. The ovary is susceptible to chemotherapy-induced damage, particularly following treatment with alkylating agents such as cyclophosphamide. Ovarian damage is drug- and dose-dependent and is related to age at the time of treatment, with progressively smaller doses required to produce ovarian failure with increasing age. Preventing chemotherapy-induced damage to the ovary or testes remains an elusive ideal in the field of fertility preservation. Both chemotherapy and radiotherapy can impair future fertility, and treatments for certain cancers can be sterilizing.
In vitro fertilization (IVF) was initially developed to treat patients with damaged Fallopian tubes. IVF treatment has since been extended far beyond tubal infertility to treat a whole host of indications, including unexplained infertility, endometriosis, and male infertility. Infertility treatments include timed intercourse, ovulation induction, intrauterine insemination (IUI), gamete intrafallopian transfer (GIFT), zygote intrafallopian transfer (ZIFT), IVF, and intracytoplasmic sperm injection (ICSI). Standard stimulation protocols require pituitary desensitization with a GnRH agonist, and this strategy has become almost a universal practise in assisted conception clinics with the induced hypogonadotropic hypogonadism enabling almost complete control over follicular development. The presence of endometrial polyps, submucous fibroids, and intrauterine adhesions may be associated with reduction in pregnancy rates and increase in risk of miscarriage with IVF. Cryopreservation of supernumerary good-quality embryos is vital to optimize pregnancy rates per cycle started without the need to superovulate the patient again.