Notice events of the menstrual cycle are coordinated such that ovulation is expected to occur at about day 14 of a 28-day cycle. An oocyte that has been ovulated survives and remains viable in the fallopian tube for only about 24 hours. If intercourse has taken place, the egg and sperm meet in the outer end of the fallopian tube, where conception may occur. The fertilized egg travels through the tube towards the uterus with the help of tiny hair-like projections called cilia which help move the egg along towards the uterus. The maximum length of time that sperm can remain viable in the female tract is 3 to 5 days. Sperm can reach an egg in the Fallopian tube within an hour after intercourse. So, the best time to get pregnant would be if intercourse occurred within a few days before ovulation to a day after ovulation. However, given the variability in menstrual cycles, the optimal time of intercourse to achieve pregnancy has potential for great variability each month.

Once the ovum is fertilized it will begin to develop. The journey to the uterus takes about 3 days. As the developing embryo, now called a blastocyst, enters the uterus it floats around for another 3-4 days as the uterus prepares for implantation. The window for successful implantation is relatively narrow and if the blastocyst does not implant at the proper time, it will not survive. Typically, implantation occurs 6-7 days after fertilization. If implantation does not occur in this time frame the endometrium will die and be sloughed off, along with the blastocyst. At about the time of implantation cells of the blastocyst begin producing hCG which keeps the endometrium functioning so that it won’t slough off. The presence of this hormone is the basis of the pregnancy test.