Reproduction, Events and Management | Pregnancy: Physiology

Successful pregnancy requires an orchestration of events between the developing conceptus and the reproductive tract in which it resides. Early in development, before the 8- to 16-cell stage, the conceptus is transcriptionally inactive and relies on mRNA inherited from the oocyte for protein synthesis. It is not until days 16–18 that the ruminant conceptus adheres to the uterine endometrium. Until this time, the conceptus is dependent upon secretions from the oviduct and endometrium for nutritional support. A key event in early pregnancy is rescue of the corpus luteum from luteolysis. This event, caused by secretion of interferon-τ by the trophoblast, allows continued progesterone secretion by the corpus luteum. Progesterone is needed for the continuation of pregnancy. At least 140 endometrial genes are upregulated by progesterone and these gene products are involved in inhibition of uterine contractions, nourishment of the conceptus, angiogenesis, regulation of immune function, and placentation. Once formed, the placenta is very efficient at transfer of nutrients to the conceptus because of the organization of the maternal and fetal vasculatures. Nonetheless, nutritional deprivation or other insults to placental function can compromise fetal development and cause adverse effects on the physiology of the offspring that can persist into adulthood.