In the fourth week of your pregnancy, the
ball of
cells that is developing into your baby is
the size
of a poppy seed.
It's at this stage that the
cells separate into 3 distinct layers from
which your baby's
internal organs and skin will develop.
The outermost layer forms
the brain, nervous system and skin.
The middle layer forms
the heart, blood vessels, bones, muscles and
reproductive system.
The
innermost layer will develop into the stomach,
intestines, lungs, and
other organs.
Your baby's first blood cells are already
being
produced in the yolk sac.
Expect big changes by the
fifth week of your pregnancy.
The ball of cells now
resembles a tadpole and it is big as a peppercorn.
The creation of the brain, spinal cord, heart,
and blood
vessels is already well under way.
The neural tube, which
will form the brain and spinal cord starts
to close
from the center of the embryo outward.
After it closes,
the portion in the head thickens and divides
into the
forebrain, midbrain, and hindbrain.
Rapid growth causes folding of the
embryo.
During this process, part of the yolk sac
is
incorporated into the lining of the digestive
system.
The primitive
backbone is curled and looks like a tail,
which will
recede in a few weeks.
Your baby's heart is transformed
from a tube into an S-shaped loop that begins
beading
about 22 days after conception.
At this point, you may
begin experiencing early signs of pregnancy
including nausea, fatigue, and
breast tenderness.
By your sixth week of pregnancy, your little
one has tripled in size and is protected by
amniotic
fluid.
The baby is grown by leaps and bounds, but
still only about the size of a lentil.
You've just
been to the OB/Gyn and she is confirmed the
good
news.
You're definitely pregnant.
You don't know if you're having
a boy or a girl yet, but you can thank
dad for your child's sex because one of two
sex
chromosomes either an X or a Y was delivered
by
the sperm determining your child's gender.
The egg always contains
an X so if the sperm contained an X, the
embryo develops into a girl.
But if the sperm contained
a Y, the embryo develops into a boy.
A gene
on the Y chromosome becomes active late in
the sixth
week, functioning for only a few days to tell
the
embryo to become a boy.
Facial features have formed and
his heart has a regular rhythm pumping fetal
blood.
Right
now because your baby's skin is only one cell
think,
it's transparent.
Little knobs protrude from the embryo's trunk.
These
buds of tissue will become arms and legs.
At the
beginning of your seventh week, your baby
is now about
the size of a coffee bean.
The umbilical cord connecting
your baby to the uterus is now visible.
The placenta
is covered with lots of small projections
called villi.
The
villi from the placenta intermingle with your
blood where they
steal some of your breakfast, lunch and dinner.
The nutrients
and oxygen travel about 18 inches through
the umbilical cord
to your growing baby.
It's too early to tell whether
your child will have your nose, but mouth,
nostril and
ear indentations are visible in the head.
The arm buds
that form last week look like paddles.
The brain is
growing rapidly including the right and left
sides of the
brain.
The right side of the brain is associated
with
nonverbal and spatial tasks.
The left side is associated with
speaking and writing.
You'll have to wait and see if
your child becomes predominantly right or
left brain.
By the
eight week, your fetus is about the size of
a
blueberry.
What were once just little tissue buds have
become
recognizable as hands and feet with webbed
fingers and toes.
Soon, this extra tissue between the digits
will be reabsorbed
to reveal individual fingers and toes.
