How a Pregnancy Begins

Biology 101: From Ovulation to Fertilization, How a Pregnancy Begins

To achieve pregnancy, the egg and sperm must meet at the right time and place in an environment that promotes fertilization. How a pregnancy begins is a complex process and may be upset by many factors.

~Each month the pituitary gland in a woman’s brain sends a signal to her ovaries to prepare an egg for ovulation.

~The pituitary hormones — follicle-stimulating hormone (FSH) and luteinizing hormone (LH) — stimulate the ovaries to release an egg. This is called ovulation. It is during this time that a woman is fertile (usually about day 14 of a 28-day menstrual cycle).

~The ovulated egg travels through the fallopian tube and can be fertilized within about 24 hours after its release. Conception is more likely to occur when intercourse takes place one to two days prior to ovulation.

~For pregnancy to occur, a sperm must unite with the egg in the fallopian tube during this time.

~Sperm are capable of fertilizing the egg for up to 72 hours and must be present in the fallopian tube at the same time as the egg for conception to occur. In order for a sperm to reach an egg, the man must have an erection and ejaculate enough semen to deliver the sperm into the vagina. There must be enough sperm, and it must be the right shape and move in the right way. In addition, the woman must have a healthy vaginal and uterine environment so that the sperm can travel to the egg.

~If fertilized, the egg moves into the uterus where it attaches to the uterine lining and begins a nine-month process of growth.

For some couples attempting pregnancy, something goes wrong in this complex process, resulting in infertility.

The cause or causes of infertility can involve one or both partners:

  • In about 40 percent of cases, infertility is due to a cause involving only the male partner.
  • In about 20 percent of cases, infertility is due to causes involving both the male & female.
  • In the 40 percent of cases, infertility is due entirely to a cause involving the female.