gynecology and obstetrics
Conception and Prenatal Development
Introduction
For conception (fertilization), a live sperm must unite with an ovum in a fallopian tube with normally functioning epithelium. Conception occurs just after ovulation, about 14 days after a menstrual period. At ovulation, cervical mucus becomes less viscid, facilitating rapid movement of sperm to the ovum, usually near the fimbriated end of the tube. Sperm may remain alive in the vagina for about 3 days after intercourse. The fertilized egg (zygote) divides repeatedly as it travels to the implantation site in the endometrium (usually near the fundus). By the time of implantation, the zygote has become a layer of cells around a cavity, called a blastocyst. The blastocyst wall is 1 cell thick except for the embryonic pole, which is 3 or 4 cells thick. The embryonic pole, which becomes the embryo, implants first. About 6 days after fertilization, the blastocyst implants in the uterine lining. 