The growth and development
stages of the baby from conception to birth
The human reproductive system contains all the organs
needed for reproduction and producing babies. Conception occurs in the
fallopian tube when male sperm meets the female egg and fertilizes it, and
begins to develop into fetus and finally a baby. During this process woman’s
body will undergo many different changes. The development stages of pregnancy
are called trimesters, or three-month period, because different changes occur
at each stage. During each stage of development, different physical changes
takes place in fetus and the baby will develop very quickly in the 40 weeks of
Weeks of pregnancy are dated from the first day of
the last period. This means that during the first two weeks you are not
severely pregnant, your body will be preparing for ovulation. The most
important time for intercourse is the two days before and the day of ovulation.
The fertilization of the egg begins when a sperm penetrates the female egg.
When sperm fertilizes a woman’s egg it becomes a zygote and during this period
the zygote will move down the fallopian tube to the uterus where it will
continue to grow and attach to the blood-rich lining of the womb. Safe inside
the uterus it changes again. A cavity forms its center, and two groups of cells
are formed. One group of cells become embryo and the other will become
placenta. In these first weeks of pregnancy, the embryo is attached to a small
yolk sac that provides food. A few weeks later, the placenta will be fully
formed and will take over the nutrient transfer to the embryo. Hormones from
the embryo now flow through blood stream; a blood test taken at now would
likely detect the pregnancy.
During this time baby’s major organs are developing
rapidly and he or she is changing from embryo to fetus. Until eight weeks after
conception the developing baby is called embryo, from eight weeks until birth,
the developing baby is called fetus. At four to five weeks the embryo is the
size of a pea and during this early stage the embryonic cells are divided into
Ectoderm- forms the outer layer of the baby, the skin, nails and hair, it folds
inwards to form the nervous system (brain, backbone and spinal cord)
endoderm- forms all the organs inside the baby.
mesoderm- develops into the heart, muscles, blood and bones.
After six weeks the embryo is about the size of a
lentil and has a heart, which beats up to, 150 per minute and arms and legs
appear as buds growing out from the embryo. By week seven the baby will be the
size of a small bean, arms and legs and even fingers will be forming. At this
point the head of the baby is far bigger than other parts and small sections
begin to be visible eyes, nose and ears. By week eight the baby will have more
developed brain and heart, and the arms will be long enough to bend and tiny
legs may meet in front of the baby.
At eight to nine weeks the unborn baby is called
fetus and measures about 2cm long, by this time baby’s face will start forming.
Toes and finger start to form and the major internal organs such as heart,
brain, lungs, kidneys and gut, continue developing rapidly. By week 10 small
things start to form on the fetus including fingernails and hair, ears start to
develop on the sides of the baby’s head and the ear canals are formed inside
the head and also jawbones start developing, already contain the future milk
teeth. By the week 11-12 babies can move fingers and toes and fingerprints
formed. The baby starts smiling, sucks, swallows and urinates. The sex of the
baby can be said at this time.
weeks the fetus has grown fully and is now around 10cm long and weighs about
100g. By 12 weeks the unborn baby is fully formed and just need to grow and
develop. By week 13 babies ovaries or testicles are fully formed and their genitals
can be formed outside the body. By week 14 babies begins to swallow little bits
of amniotic fluid which passes into the stomach and kidneys start functioning.
Around week 15 babies start to hear from outside the world and any noises
digestive system makes. They also start becoming sensitive to the light. By
week 16 muscles of the baby’s face can move and have a fully working
circulatory system and urinary tract.
At these weeks the fetus is large enough for the
mother to feel its movements. By the 17th week of pregnancy, the baby grows rapidly
and weighs around 150g. The baby’s eyes now move although the eyelids are still
closed and the mouth can open and close. The baby moves a little and reacts to
the loud sounds from the outside world, such as music. The week 20 reproductive
organs and genitalia are now fully formed and may able to know the sex of the
baby by ultrasound. At this point in pregnancy the baby’s skin is covered in a
white greasy protective film called vernix. This will protect the skin of the
baby for a long period of time in the amniotic fluid and will also help during
By 20 weeks the baby weighs around 350g, at this time
the baby becomes covered in a very fine, soft hair called lanugo. It keeps the
baby in the right temperature and usually disappears before birth. The baby
starts responding to sounds by moving or increasing the pulse and may notice
jerk motions if baby hiccups. The lungs still cannot function properly, but the
baby is practicing breathing movements to prepare for life outside the womb.
The baby gets all its oxygen from the mother via the placenta and will do so
until it’s born. In the 24th week pregnancy the baby has a chance of survival
if he or she is born. Longevity babies cannot survive because of the lungs and
other vital organs aren’t developed enough.
During these weeks the baby will be around 14 inches
long and weighs around 900g. The baby moves heavily and responds to touch and
sound. A very loud noise may make the baby jump or kick, and the mother will
able to feel it. By the time the baby is 24-28 weeks he or she starts urinating
into the amniotic fluid. The baby’s eyelids are opened for the first time and
will soon start blinking. By week 28 the baby is active and initial breathing
movement begins, and heartbeat falls to 140 per minute and can be heard with the
help of a stethoscope. By 28 weeks baby weighs around 1 kg and is perfectly
From 28 weeks the fetus is said to be viable- that is
if born now, the baby has a good chance of surviving, although the babies have
survived from as early as 23 weeks. The baby will be around 15 inches long and
weighs around 1.5 kg. The baby grows plumper, and the skin begins to look less
wrinkled and much smoother. The white, greasy vernix and the soft, furry lanugo
that covered the baby’s skin for some time begin to disappear. The lungs and
digestive system will be functioning and fully developed. The lungs are
developing rapidly but the baby wouldn’t be able to breath on its own until
about 36 weeks.
In this weeks baby may be around 18 inches and weighs
around 2-2.5kg. The baby will continue to mature and develop reserves of body
fat. Baby’s brain is developing rapidly at this time, and the baby can see and
hear. The most internal systems are well developed but the lungs may still be
immature. By week 32, the baby lays their head downwards i.e.. ready for birth.
This is known as cephalic presentation. Movements of the baby will be at
maximum and kicks and squirms will be felt and organs will continue to mature.
By 36 weeks baby’s lungs are fully formed and ready to take their first breath
By 36-38 weeks the baby is 20 inches long and weighs
2.5-3kg. In the last weeks some time before the birth, the baby’s head should
move down into the pelvis. The baby will be fully developed. Have instincts and
be ready for the first day of life. The final stages of pregnancy can be
extremely uncomfortable for a woman. We may notice that the baby moves less due
to tight space. Baby’s position changes to prepare itself for labor.