Only about 30% of successfully fertilized oocytes result in the delivery of a living child. This chapter summarizes current knowledge on the epidemiology, diagnosis, and treatment of first-trimester pregnancy loss. First-trimester pregnancy loss is a common event, experienced by about 25% of all women during their reproductive career. Clinical characteristics of women presenting with first-trimester bleeding are of little value in correctly predicting a miscarriage. The most constant sonographic findings indicative of a miscarriage are those of an empty gestational sac, where no yolk sac and no embryonic pole are present, or the finding of an embryo or fetus without cardiac activity. More recently, progesterone has also been applied in the prevention of miscarriages. At present, three different treatment options are being used in managing first-trimester miscarriages: expectant, surgical and medical management. The available knowledge from randomized controlled trials comparing various treatment options for miscarriages has been systematically reviewed.

This chapter reviews the roles and distribution of O2 inside the early human gestational sac and its impact on our understanding of the physiology of O2 metabolism by the fetus during the first and early second trimesters of pregnancy. The mammalian fetus is exposed to major fluctuations in O2 concentration from conception to delivery. The first trimester gestational sac has additional barriers to materno-fetal exchange compared to the definitive placenta of the second and third trimesters of pregnancy. Ample dilation of the uteroplacental circulation together with rapid villous angiogenesis are the key factors necessary to adequate placental development and function and subsequent fetal growth. Overall the data have confirmed that the human placenta is not truly hemochorial until the end of the first trimester. Rather it is deciduochorial, being supported by tissue fluids and endometrial secretions.

Power Doppler ultrasound (US), in combination with three-dimensional US and virtual organ computer-aided analysis (VOCAL), is a very good approach for investigating the global ovarian vascular network and its correlation with ovarian response in assisted reproductive technology (ART). An ovarian vascular map is easily obtained from a sagittal section of the ovary. Three-dimensional US has become a key tool for diagnosing uterine malformations. Leiomyomas and endometrial polyps are the most frequent benign uterine pathologies, and both can interfere with the reproductive process. The human endometrium undergoes intense angiogenesis during menstrual cycle, and angiogenesis is a key process for successful embryo implantation and development. In reproductive medicine, it is crucial to exclude ectopic pregnancy as early as possible. 3D US is a more accurate technique for evaluating the relationship between the gestational sac and uterine septum and for differentiating between a cornual pregnancy and a displaced intracavitary pregnancy.

When clomiphene citrate (CC) is used for ovulation induction, endometrial thickness is often decreased compared with spontaneous cycles during and immediately following the days CC is taken, because of its antiestrogen effect. A triple-line pattern on the day of human chorionic gonadotropin (hCG) administration has been reported to be necessary for implantation in controlled ovarian hyperstimulation (COH) cycles, where human menopausal gonadotropin (hMG) or follicle stimulating hormone (FSH) is administered. A triple-line endometrial pattern on the day of hCG administration in in-vitro fertilization (IVF) cycles is related to serum estradiol level, the number of mature oocytes, and the number of top-quality embryos and is unrelated to serum progesterone levels. Preclinical miscarriage, also referred to as biochemical pregnancy, in which quantitative hCG levels initially indicate pregnancy but decrease before a gestational sac can be seen on ultrasound, and clinical miscarriage of embryos with karyotype is the result of inadequate endometrial development.