This animation will show how your baby develops during pregnancy.
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This animation contains sound.
Pregnancy usually lasts about nine months, or 40 weeks,
and is divided into trimesters.
The first trimester is from week one until week 12.
The second trimester is between weeks 13 and 26,
and the third trimester
is from week 27 until birth
If you become pregnant, your womb doesn't shed its lining as it normally does
at the end of the menstrual cycle,
so your periods temporarily stop.
This is because the egg,
which has been released from one of the ovaries,
has been fertilised by a sperm
and you are in the early weeks of pregnancy.
Here we show the ovaries,
the fallopian tubes, the womb and the vagina.
The fertilised egg has already started to divide in the fallopian tube.
It will continue to develop and grow in the womb
and is called an embryo at this stage.
Here we show the embryo in the womb.
By week nine
the embryo has developed and is called a fetus.
At this point most of the organs, including the nervous system and heart
are forming.
Here we show the fetus in the womb.
By the time you are 12 weeks pregnant,
your baby is approximately
6cm (two and a half inches) long.
At this stage,
your baby's neck is uncurling
and the limbs are complete.
The eyelids are still fused
and the ears are forming.
Here we show the baby,
the umbilical cord,
the placenta
and the amniotic fluid.
The umbilical cord connects the baby to the placenta.
This is how your baby gets nutrients and how waste (such as urine) is removed.
In the second trimester, your baby's sex organs develop
and other organs mature.
The baby swallows amniotic fluid
and passes it out through its digestive system.
The kidneys start to work
and pass small amounts of urine.
Your baby can now hear,
and is covered in fine hair
called lanugo.
Here we show the baby in the second trimester.
You may first feel the baby move in the second trimester of pregnancy.
The movements become much more vigorous and obvious
as the baby gets bigger and stronger.
Braxton Hicks (practice contractions)
are painless tightenings of the womb
that may start from around 20 weeks of pregnancy.
Your baby's lungs mature throughout the third trimester.
The baby makes breathing movements, even though the lungs don't work properly
until birth.
The baby grows fine hair and fingernails,
the eyes open and close,
and teeth may start growing under the gums.
Your baby's fat stores also increase in preparation for birth.
Braxton Hicks contractions become stronger in the third trimester.
At the end of your pregnancy
your baby changes position so it is ready for birth.
The baby's head may not engage,
that is,
move into the position in the pelvis for birth, until labour
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