Early pregnancy, starting at conception and ending with the completion of embryogenesis, is a period of rapid growth and development of both embryo and placental tissues. Early disruption of embryonic development has major consequences, which are discussed in this chapter. Gestational trophoblast disease is rare and occurs when the embryo’s genetic material is polyploid or of monoparental origin, and can result in gestational trophoblast neoplasm. Miscarriage is common and reflects early embryonic developmental arrest and demise, e.g. due to chromosomal abnormalities. Ectopic pregnancy occurs when implantation takes place at any site other than the uterine cavity, usually the fallopian tube. Each of the disorders frequently present with bleeding in early pregnancy. Finally, and in contrast to the previous three disorders, hyperemesis gravidarum, or excessive vomiting in pregnancy, is likely a result of the surge in placental hormones in early pregnancy that marks a healthy placental development.
