Most women are able to become pregnant from
puberty, when their
menstrual cycles begin, until
menopause, when their cycles stop. A pregnancy starts
with fertilization, when a woman's egg joins with a man's sperm. Fertilization
usually takes place in a
fallopian tube that links an ovary to the uterus. If
the fertilized egg successfully travels down the fallopian tube and implants in
the uterus, an embryo starts growing.
Ovulation, fertilization, implantation
All the eggs
for a woman's lifetime are stored in her ovaries. Women do not keep
producing eggs. This is different from men, who continuously make more
About once a month,
an egg is released from one of a woman's two ovaries. This is called ovulation.
The egg then enters the nearby fallopian tube that leads to the uterus.
If a woman and a man have unprotected sexual intercourse, sperm that is
ejaculated from the man's penis may reach the egg in the fallopian tube. If one
of the sperm cells penetrates the egg,
the egg is fertilized and begins developing.
The egg takes several
days to travel down the fallopian tube into the uterus. After it is in the uterus, a
fertilized egg usually attaches to (implants in) the lining of the uterus
(endometrium). But not all fertilized eggs
successfully implant. If the egg is not fertilized or does not implant, the
woman's body sheds the egg and the endometrium. This shedding causes the
bleeding in a woman's
When a fertilized egg does implant, a hormone
called human chorionic gonadotropin (hCG) begins to be produced in the uterus.
This is the hormone that a pregnancy test measures. It prevents the uterine
lining from being shed, so the woman does not have a period. Other signs such
as breast changes and nausea occur in a woman's body, also meaning that
pregnancy has begun.