Fertilization

Fertilization occurs when a sperm penetrates the outer layer of the egg. An egg must be fertilized within 12 hours of ovulation. If it is not fertilized within that time, it dies and is absorbed by the body.

If the egg is fertilized, it starts to develop and slowly descends toward the uterus to form an embryo. It will implant itself in the lining of the uterus, which is called the endometrium. Implantation takes place about seven days after ovulation.

Most women take a pregnancy test when they realize their period is late. If the test is positive, it means the egg was fertilized by a sperm.

In about one out of every six pregnancies, the embryo will not develop or the baby’s heart will stop beating relatively early on. The uterus will then stop growing and expel its contents, ending the pregnancy in miscarriage.

The risk of miscarriage increases with age. One in four pregnancies in women 35 and over ends in miscarriage; in women 40 and older, the risk is one in two.

In some rare cases (2% to 4% of pregnancies), the embryo implants itself outside the uterus. This is what is called an ectopic pregnancy.

Female anatomy

  1. Pelvis: Bone that supports the organs in the mother’s abdomen.
  2. Ovaries: The two ovaries produce eggs and female hormones.
  3. Uterus: Muscular organ that grows as the pregnancy progresses. Normally, it is the size of a small upside down pear.
  4. Fallopan tubes: Tubes connecting the uterus and the ovaries. They transport eggs and are necessary for fertilization.
  5. Cervix: Bottom part of the uterus connected to the vagina. During menstruation, blood flows from the cervix, which is almost closed. During labour, the cervix dilates to let the baby through.
  6. Vagina: A roughly 8 cm long passageway between the uterus and the vulva. The vagina is flexible and elastic so it can stretch during intercourse and delivery.
  7. Bladder: Organ that holds the urine produced by the kidneys.
  8. Perineum: Viewed from the exterior, the region between the anus and the vulva. The muscles of the perineum form a sort of internal “hammock” that supports the genital organs and bladder.
  9. Anus: Opening through which feces are expelled.
  10. Urethra: Tube that carries urine from the bladder to the outside of the body during urination. It is part of the perineum.
  11. Clitoris: Sensitive, erogenous organ that plays an important role in female sexual pleasure.
  12. Vulva: All external genitalia, including the labia and clitoris.

 

 

 

Male anatomy

  1. Bladder: Organ that holds the urine produced by the kidneys.
  2. Vas deferens: Tube that carries sperm from the testicles to the prostate.
  3. Urethra: Tube that carries urine from the bladder and out the penis. It also carries semen from the prostate and out the penis.
  4. Penis: Male sex organ. Its sponge-like tissue swells with blood during erections.
  5. Prostate: Gland that secretes seminal fluid, one of the substances found in semen.
  6. Scrotum: Sac of skin that protects the testicles.
  7. Testes: Organs that produce sperm.
  8. Seminal vesicles: Reservoirs above the prostrate that store sperm that are ready to fertilize eggs.
  9. Anus: Opening through which feces are expelled.

 


Illustrations: The Pregnancy Book
Adapted by Bertrand Lachance
with the permission of the Department of Health, UK

Miscarriage: A spontaneous abortion, which can have a variety of causes (e.g., a deformity or disease).