ABSTRACT
The cell that is formed by fusion of the sperm cell and ovum at fertilization is termed the zygote, and this cell divides many times over to form a ball of cells that can implant in the wall of the uterus and develop into an embryo, placenta, and embryonic membranes (together termed the conceptus). Pregnancy is confirmed clinically when a woman misses her menstrual period and the hormone human chorionic gonadotropin (hCG) is detected in her blood or urine. hCG is a glycoprotein hormone produced by the developing conceptus that serves to maintain the corpus luteum in the ovary of the pregnant woman until the placenta becomes established and can begin to produce estrogen and progesterone. Following a positive pregnancy test, the pregnancy is deemed, by convention, to have started on the first day of the woman’s last menstrual period (LMP). A normal pregnancy lasts 40 weeks and is split into three trimesters, each lasting 3 months. The stages of pregnancy are outlined in Table 12.1.
