Where Conception Takes Place

Two common misconceptions are that conception occurs in the woman’s uterus and that a fetus’s gender is determined after conception. Here’s what happens.

During sexual intercourse:

  • The man’s sperm (from 100 million to 300 million) are ejaculated in the woman’s vagina. (Sperm can live up to five days after ejaculation into a woman.)
  • The sperm travel through the small opening of the cervix into her uterus, using the force of their ‘tails’.
  • The sperm swim through the uterus, and then propel themselves into the fallopian tubes.
  • If the woman has ovulated within the past 24 hours or so, and a viable egg has been released from an ovary, the egg will be in the fallopian tube ready for fertilization.
  • When one sperm penetrates the egg’s mucus layer, the egg and sperm unite.  Viola! Conception (fertilization) occurs —in the fallopian tube.
  • At conception, the gender is determined — the sperm that fertilizes the egg is carrying either a female (X) or male (Y) chromosome.
  • This fertilized egg then migrates down into the uterus, where, if all goes well, it will implant in the uterine lining. This is when a pregnancy technically occurs.

Using in vitro fertilization (IVF): 

  • Several eggs are extracted from a woman’s ovaries in a simple surgical procedure that requires local anesthesia. They’re placed in a lab dish in a solution.
  • Sperm (from a partner or donor) are then placed in a lab dish along with the egg(s).
  • The sperm swim to the eggs. One sperm penetrates each egg membrane — fertilization occurs — and an embryo forms.
  • Pregnancy occurs when the embryo(s) are transferred to the uterus and successfully attach to its lining.

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