Development of the embryo is governed internally by genes inherited from the parents,and externally by factors such as the woman's
diet and any drugs taken during pregnancy.
The first two weeks
The embryo develops from an egg that has been fertilized by a sperm .It starts as a single cell -just large enough to be seen by naked eye.As a fertilized egg travels along the tube to the uterus,the cell divides in two.These two new cells divide form for cells.Cell divisions
continue ,each time doubling the number of cells.
The cells form a spherical mass ,in the center of which a hollow depression develops.Within the sphere ,the cells then form in two two very distinct groups;one makes up the wall lining the
sphere:the other expands to form the embryo itself.
On about the sixth day the sphere of cells become attached to and then embedded in the lining of the uterus.At the site of attachment the outer layer of cells obtained nourishment from the woman's blood;that part of the outer layer will later develop into the placenta.Two bubbles from side by side with in the cell mass.Between the bubbles a flat disk forms,consisting of layers of cells from which all the baby's tissues and organs will form.The amniotic sac develops around the growing embryo.
Third week
Early in the third week, the disk of cells becomes pear shaped>The head of the embryo formes at the rounded end and the lower spine at the pointed end.A group of cells develops along the back of the embryo to form the notochord, a rod of cells that constitutes the basis of the spine.From this time on ,the embryo has two recognizable halves that develop more less symmertically.
The notochord then furrows and the edges grow towards each other before fusing to form the nural tube.Later the nural tube will develop into the brain and spinal cord.
The forth week
During the forth week the embryo becomes recognizable as a mammal.the back grows more
rapidly than the front.,giving the embryo a C- shape,and a tail becomes visible.Withe
in the embryo, buds of tissues that will later develop into the lungs,pancreas, liver
and gallbladder.The natural tubes extends towards the head of the embryo,where the
broad fold becomes visible that eventually will grow into the brain.
The developing ears first appears as pits.Rudimentary eyes heart develops in the
form of stalks.The outer layers begin to form the limb buds and the branchial arches
(folds of tissues)that are later to become the jaws and other structures in the neck.
paired bulgers appears on the sides of the natural tube that will become the
cartilage,bone and and the muscle of the back.On the front of the embryo,just
beneath the head ,a rudimentary heart develops in the form of a straight tube.
As the branchial arches develop,The heart is push down into the chest.It is
during this period that the embryo is at the greatest risk of of both defect
caused by abnormal genetic or external factors.
The fifth week
The external years become visible, pits mark the position of the developing nose,
the upper and the lower jaws form,and the limb buds extend, becoming flattered
at the end where the hand and feet will develop.The two folds of tissue meet at
the front of the embryo and fuse to form the front wall of the chest and
abdomen.The umbilical cord develops.
The sixth week
Baby’s brain and nervous system are developing at a rapid pace.
The larynx starts to form as does the inner ear. Optic vesicles, which later
form the eyes, begin to develop this week on the side of the head, as do the
passageways that will make up the inner ear. The head and tail of the embryo are
formed, limb buds are present, and basic facial features begin to appear.
Because their legs are curled up against the torso for much of the pregnancy,
making a full-length measurement difficult, babies often are measured from the
crown to rump rather than from head to toe. In week 6 of pregnancy, your baby is
0.08 to 0.2 inches from crown to rump.
The seventh week
- The hand plates become present this week, and the baby is 0.2 to 0..52
inches long, or about the size of a marble. He or she weighs about 0.03 ounces..
The genital tubercle is present, but you can't distinguish girls from boys
by sight at this point. Nasal pits are forming.
Your baby will actually go through 3 sets of kidneys, very rapidly as they
develop during this period. This week the second of such sets will form. Your
baby’s heart becomes completely formed , the limb buds are present and the
eyes appear as dark spots with the eyelid folds forming. Your baby’s tongue
begins to form and his or her trunk of their body elongates and straightens. The
pituitary gland is forming in the middle of the brain.
The stomach and esophagus begin to form and the umbilical cord, which is the
link between your baby and the placenta, is now clearly visible. Your baby’s
liver starts functioning also this week. Your baby will also start producing red
blood cells.
The eight week
Baby will likely begin developing webbed fingers and toes. This
week your baby's gonads will become either testes or ovaries. Elbows appear
and the process of ossification (hardening of the bones) begins. The leg buds
divide into thigh, leg, and foot units and the arm buds divide into hand, arm,
elbow, and shoulder units. Your baby’s arms and legs will begin to move
spontaneously. The baby’s eyelids begin to form, the ears, upper lip, and tip
of the nose become recognizable and the tongue begins to develop. Teeth are
developing under the gums.
The ninth week
Your baby may be roughly one inch long. Your baby also weighs in at
roughly one ounce. Your baby’s physical body including their arms, legs and
head has taken shape. The embryonic tail at the bottom of your baby's spinal
cord is shrinking, and your baby's head is now nearly half the size of its
entire body.
More fetal developments that typically occur during the ninth week of pregnancy
are the formation of nipple and hair follicles, the abdomen and chest cavities
become separate, the eye muscles and upper lip develop the nerve cells of the
retinas form in the eyes and the semicircular canals of the ears form. At this
point, all your baby’s fingers and toes are present. The urinary and rectal
passages are completely separate and the intestines start to move out of the
umbilical cord and into the abdomen.
The tenth week
Baby is now 1.25 to 1.68 inches long and weighs approximately
0.18 ounces. In week 10 of pregnancy your baby now enters its fetal period. Tiny
toes have formed. The eyes are largely open, are no longer transparent. External
genitalia are beginning to differentiate. External ears are completely formed,
as well as the upper lip. As external changes such as the separation of fingers
and toes and the disappearance of the tail takes place, internal developments
are taking place too. Tooth buds form inside the mouth, and if you're having
a boy, his testes will begin producing the male hormone testosterone. The two
lobes of the lungs extend into many tiny tubes (bronchioles) and the diaphragm
begins to separate the heart and lungs from the stomach, which moves into its
final position.
The eleventh week
Your baby is almost large enough for you to nestle in your palm. Most
babies are just under 1 ½ inches long by now and may weigh as much as .3
ounces. Your baby’s skin is still transparent, once your baby reaches full
term he will start to fill out, and you will no longer be able to see your
baby’s blood vessels showing through his skin. Most babies will double their
size during the next three weeks. The iris will begin to develop this week and
finger nails appear. Week 11 of pregnancy marks the end of the embryonic period.
From now on, your baby is called a fetus. It also marks the period when your
baby is out of the danger zone for the development of most congenital
abnormalities. Other developments that are happening around this time are the
external genitals move outside of the body , the hair follicles of the skin are
forming , and teeth are beginning to form.
The twelfth week
Your baby is about 2.5 inches long and weighs approximately 0.3 to
0.5 ounces. Your baby's brain continues to develop, and tiny fingernails and
toenails start to form. Vocal cords are formed this week, which is the last of
your first trimester. Your baby's kidneys are functioning, as is the liver.
They thyroid gland and pancreas are also complete. Your baby is now passing
urine and the gall bladder secretes bile. After swallowing amniotic fluid, your
baby will now be able to pass it out of the body as urine. A skeleton made of
cartilage is forming.
The thirteenth week
Your baby is actually quite large by now, a whopping 3 inches long in
some cases and weighs in at roughly .7 ounces. By 13 weeks pregnant your
baby’s intestines are working on maturing and your baby’s tiny pancreas is
working hard to produce insulin.. This will help your baby regulate her blood
sugar levels in the months and years following delivery. Your baby’s eyes also
start to move closer to the center of your baby’s head. The head can move
easily from side to side and up and down, and the facial features are starting
to form. Your baby’s arms have almost reached final proportion and length,
though the legs are still quite short relative to the baby's body. At 13
weeks pregnant, your baby can now probably flex its arms and kick its legs. He
or she may also be able to put a thumb in his or her mouth, although the sucking
muscles are not yet completely developed. The sockets for all twenty teeth are
formed in the gums, and vocal cords are beginning to form. Other things
happening at this time are the appearance of fingernails, the beginnings of
fingerprints and footprints, the start of vocal cord formation, the appearance
of visible ribs. The trachea, lungs, stomach, liver, pancreas, and intestines
are developing into their final functioning form.
The fourteenth week
Your baby is about 3 to 4 inches long. He or she weighs about 1
ounce. All of the baby’s nourishment is being received from the placenta. The
placenta has also taken over all hormone production from the ovaries. These
hormones will continue to play a vital role in maintaining your pregnancy along
with the changes in your body. Your baby is now producing urine and actually
urinating into the amniotic fluid. It also can practice "breathing"
the amniotic fluid in and out of its lungs. Your baby will start to get covered
with a soft, fine hair over its body called lanugo. The lanugo will be shed
before he or she is born and replaced with thicker, coarser hair. Your
baby's sex organs have fully differentiated into male or female. Other fetal
development that occur around week 14 of pregnancy include the ears having moved
from the neck onto the head, complete digestive glands, the thyroid starts to
produce hormones, and the vocal chords are complete. Your baby will begin to
inhaling and exhaling.
The fifteenth week
Your baby is a about the size of an orange and between 4 and 4 and ½
inches long and weighing more than 1 ½ ounces. This week your baby will start
producing lanugo, which is fine hair that will cover your baby's body up
until a few weeks before birth. Your baby’s bones are starting to get harder
during pregnancy at 15 weeks and will continue to do so throughout your
pregnancy. Your baby is spending most of his time practicing breathing, by
inhaling and exhaling amniotic fluid. This helps your baby's air sacs
develop during pregnancy. Your baby continues to form taste buds at this point
in time. Your baby’s legs are longer than his arms at this point. Eyebrows and
hair may appear, and if your baby is going to have dark hair the hair cells
which color it will start to produce their color.
The sixteenth week
Your baby is between 4 and 4.5 inches from crown to rump and weighs
about 3 – 3.5 ounces. Your baby's nails are well formed, and some babies
are even in need of having their nails trimmed at birth. The ears have also
moved from the neck to the head. Your baby can hold his or her head erect, and
the development of facial muscles allows for a variety of expressions, such as
squinting and frowning. The stomach is producing digestive juices and the
kidneys are producing urine. Your baby is well on its way to being a little
person!
The seventeenth week
Your baby is now 4.4 to 4.8 inches long and weighs about 4 ounces. The
placenta is growing to accommodate your baby’s needs . It now contains
thousands of blood vessels that bring nutrients and oxygen from your body to
your baby's developing body. Other developments with your baby at 17 weeks
include developing reflexes that will enable your baby to swallow, blink and
suck. The circulatory and urinary systems are working. Lanugo (a soft, fine
hair) covers your baby's shoulders, back, and temples.
The eighteenth week
Your baby measures about 5 to 5..6 inches from crown to rump and
weighs about 5.25 ounces. The rapid growth spurt is slowing down during this
time, but your baby's reflexes are still developing quickly. Your baby can
now yawn, stretch, and make facial expressions. Ears move to their final
position and they stand out from the head. Your baby's eyes are also
developing — they're now facing forward rather than to the sides. The
skeleton can be clearly outlined in the ultrasound of the fetus, and the bones
begin to harden. Make sure you are getting enough calcium! Your baby's taste
buds are beginning to develop and pads (the fatty, soft parts) are forming on
the fingertips and toes. If your baby is a boy, his prostate gland is beginning
to develop. The bones in the inner ear and the nerve endings from the brain are
developed. This means that your baby will hear sounds such as your heartbeat and
blood moving through the umbilical cord.
The nineteenth week
Your baby is about 5.2 to 6 inches long and weighs about 7 ounces..
Your baby is also getting a lot more active by kicking, turning, twisting,
moving its arms, and wiggling its fingers and toes. This may feel as if you have
butterflies; a lot of first-time mothers may not feel the classic kicking until
they are 26 weeks pregnant. At 19 weeks your baby starts to develop brown fat,
which will help keep your baby warm after birth. During the last trimester, your
baby will add more layers of fat for warmth and protection. Your baby is now
covered with a white, waxy substance called vernix caseosa, which helps prevent
delicate skin from becoming chapped or scratched. Premature babies may be
covered in this cheesy coating at delivery. The skin is developing and is
transparent, appearing red because blood vessels are visible through it. Your
baby is developing nerves that connect the muscles to the brain.
The 20th week
Your baby measures about 5.6 to 6.4 inches and weighs about 9 ounces.
Your baby is starting to grow hair on his or her head, eyebrows are forming and
if your baby is a girl her uterus is now forming. Nail growth begins. Your baby
can hear sounds now, and it will cover its ears with its hands if a loud sound
is made near you or move if it is startled.
The 21st week
Your baby could measure about 10 inches from head to toe and weighs
about three-quarters of a pound. The eyebrows and eyelids are fully developed
and the fingernails cover the fingertips. Babies are more active at this stage,
as they still have lots of room to move around. You’ll feel a lot more
movement from your little one.
The 22nd week
Your baby is about 7.6 inches long and weighs about 12.3 ounces. Your
baby's muscles are developing and becoming stronger week by week. During
week 22 of pregnancy, your baby will respond regularly to sound, rhythm, and
melody. The sounds that your baby hears in your womb will soothe him or her
after birth. At this point in your pregnancy, your baby's brain and nerve
endings are formed just enough so that the baby can feel touch. Other
developments include the eyelids and eyebrows becoming well developed, the
fingernails are completely formed, and taste buds have started to form on your
baby’s tongue. Baby boys’ testes have begun to descend from the abdomen to
the scrotum and baby girls uterus and ovaries are in place and the vagina is
developed.
The 23rd week
Your baby weighs a little over one pound and measures about 11.5
inches from head to toe. Your baby will begin to move the muscles in its
fingers, toes, arms, and legs more regularly, which may cause you to feel more
forceful movements in your abdomen. From this point on your baby will start
gaining approximately 6 ounces of weight per week. Your baby’s eyebrows and
eyelashes are forming, and the facial features such as lips and eyes are
becoming more distinct. The bones in your baby’s middle ear begin to harden.
Your baby's body is becoming more proportione
The 24th week
Your baby is approximately 1 1/4 pounds and is 8"-10" in
length. This is an active time, with lots of movement going on. With a handheld
fetal doppler, your healthcare provider will be able to pick up the heartbeat of
your baby. This common, painless test uses sound waves to listen to the blood
going through your baby's heart, allowing you to listen to the heartbeat. It
is without a doubt, one of the sweetest sounds of pregnancy. Your baby's
heartbeat will be very fast -- it is usually twice the average rate of an adult,
varying between 110 bpm and 170 bpm (beats per minute).
The 25th week
When you are 25 weeks pregnant, your baby is starting to gain weight.
By pregnancy week 25 your baby is approximately 1 ½ pounds and just under 9
inches long. From this point on however your baby's weight and length may
vary somewhat. Every baby is different as you'll soon realize during your
pregnancy week by week. Other fetal development that is occurring when you are
25 weeks pregnant includes the following:
• The structure of the spine begins to form
• Taste buds are forming
• If you are having a boy, his testes have dropped into the scrotum
• If you are having a girl, the vagina has hollowed out
• The hands are fully developed -- fingerprints and all!
• The blood vessels of the lungs are developing
• The nostrils are beginning to open.
The 26th week
Your baby will be about 9.2 inches long and will weigh around 2
pounds. He or she is still wrinkly, but will continue to gain weight and fill
out as time goes on. Although your baby's eyes have been sealed shut for the
last few months to allow the retinas to develop, they are likely opening and
beginning to blink during week 26 of pregnancy. Your baby begins to make
breathing movements (although there is no air in the lungs) and will respond to
touch. The eyelids, eyebrows, and fingernails are still developing.
The 27th week
Your baby is over 2 pounds and is almost 15 inches long. Your baby is
now perfectly formed, though she still has a lot of growing to do in the
upcoming weeks. The internal organs and systems continue to grow, mature and
develop. Around this time your baby’s eyelids will open (up until this point
in time they were fused together). Sometime around weeks 27 to 28 they finally
open. During this time the retina of the eye also starts maturing, allowing your
baby’s eyes to finally receive light and translate images. The forebrain grows
to cover the rest of the brain, resulting in some important brain development.
Your baby's muscle coordination will allow him or her to start thumb
sucking. This activity calms your baby and strengthens cheek and jaw muscles for
nursing. Your baby will be taking some breaths, and although breathing in, it is
good practice for the lungs. Your baby may be able to recognize your voice and
your partner's voice
The 28th week
Your baby now weighs about 2 to 3 pounds and measures about 15 inches
from head to toe. During this week, your baby will grow another one-half inch in
size. The folds and grooves of your baby's brain continue to develop and
expand. In addition, your baby continues to add layers of fat and has continued
hair growth. The baby’s eyes can now open and close and their muscle tone is
increasing. Although lungs are still immature, they are capable of sustaining
life in the event of a premature birth (with some medical help).
The 29th week
Your baby now weighs around 2.5 pounds and measures about 13-15
inches long from head to toe. At this stage a fetus's eyes are almost always
blue and can distinguish bright sunlight or artificial light through the uterine
wall. Your baby's movements may not be as acrobatic since space has become
more cramped, but you will still feel a lot of kicking and stretching. In boys,
testicles descend from near the kidneys through the groin en route to the
scrotum. In girls, the clitoris is relatively prominent because it's not yet
covered by the still-small labia. These will grow to cover it in the last few
weeks before birth. Your baby's head is getting bigger, and brain growth is
very rapid at this time. Nearly all babies react to sound by 30 weeks. Your
baby's nutritional needs reach their peak during the third trimester.
You'll need plenty of protein, vitamin C, folic acid, iron, and calcium
(about 200 milligrams is deposited in your baby's skeleton every day), so
eat foods rich in these nutrients. The skeleton hardens even more and the brain,
muscles, and lungs continue to mature.
The 30th week
Your baby weighs about 3 pounds and measures about 10.8 inches from
crown to rump., your baby continues to gain weight and layers of fat. From this
point on your baby will gain about a half a pound a week. In male babies, the
testicles move from near the kidneys through the groin en route to the scrotum.
In female babies, the clitoris appears large and exposed because it is not yet
covered by the folds of the skin called the labia. Your baby’s head is gettin
larger, more in proportion with its body. Your baby’s eyelids now open and
close. The bone marrow is now responsible for making red blood cells.
The 31th week
Your baby is entering a growth spurt. For the next eight weeks,
he'll gain weight faster than he increases in length, at the rate of about
half a pound a week. The bigger he gets, the harder it will be to
"see" him on ultrasound and get a good estimate of his size--the
margin of error increases to 15 percent by the end of the third trimester.
He's definitely growing fast, and you'll notice that his kicks will
start to feel more like squirming as he runs out of room to roam. Your baby will
be weighing in at around 3 1/2 pounds and measures nearly 14 1/2 inches from
head to toe. Your baby's growth weight may begin to slow down a little now,
but although it is slowing down the internal organs will continue to grow and
develop.
The 32nd week
Your baby is about 4 pounds and 11.4 inches from
crown to rump, your baby would have an excellent chance of survival outside the
womb if you delivered now.
Your baby is larger, so there will be less room for him or her to move around.
His or her kicks or movements may be less frequent.
The final touches are being placed on your baby masterpiece. Eyelashes,
eyebrows, and the hair on your baby's head are evident. The lanugo hair that
has covered your baby since the beginning of the second trimester is falling
off, although some may remain on the shoulders and back at birth.
32 weeks - All of your baby's five senses are also functional,
including hearing. This means that your baby is becoming familiar with all sorts
of noises within his or her surroundings, including your heartbeat and
digestion. Your baby’s arms and legs are fully proportioned in relation to the
size of the head. His or her hair on their head continues to grow while the
lanugo continues to fall off.
The 33rd week
Your baby measures about 12 inches from crown to rump and weighs about
4.4 pounds Throughout the next few weeks, your baby will gain more than half
of his or her birth weight. Some babies have full heads of hair by now; others
have only a bit of fuzz. If your baby is a boy, the testicles are descending
into the scrotum. All five senses are developed and your baby can listen, feel,
and see. Your baby’s eyes can detect light and the pupils can constrict and
dilate in response to light. Your baby's lungs are almost completely
matured. Fat will continue to be deposited on your baby's body for
protection and warmth. Babies gain a good deal of their weight in the final few
weeks before birth. Around this time your baby’s skin color turns from red to
pink.
The 34th week
Your baby now measures about 12.8 inches, crown to rump, and
weighs about 5 pounds. The vernix coating on the baby's skin is becoming
thicker, whereas lanugo hair is almost completely gone. The skeleton is
finishing hardening, and your baby is developing immunities to fight infections.
Your baby’s fingernails have reached the tips of their fingers. By now most
babies will be in position for delivery. Your health care provider can tell you
if your baby is positioned head down or breech (bottom-first). Babies who are
born at 34 weeks can usually survive outside of the womb without extensive
medical intervention.
The 35th week
Your baby now measures about 12 inches from crown to rump and likely
weighs more than 5 pounds, 5 ounces. This week begins your baby's most rapid
period of weight gain — about 8 to 12 each week Babies who are born during
this week or after have a 99 percent chance of survival.. If your baby is a boy,
his testes have completed their descent. He or she is continuing to gain weight
and store fat all over his or her body. The lungs are almost fully developed.
The 36th week
Your baby is now probably about 13 inches long from crown to rump
and weighs about 6 pounds. Your baby is filling out, with very little wrinkling
left. There is fat on your baby’s cheeks, and powerful sucking muscles also
contribute to your baby's full face. By this week your baby’s gums have
become rigid and their sucking muscles are fully developed. The brain is
developing at an amazing pace. Your baby is finishing the final touches in
preparation for birth.
The 37th week
Your baby weighs close to 6.5 pounds and may be about 20 inches long
from head to toe. Your baby's head is now cradled in your pelvic cavity --
surrounded and protected by your pelvic bones. This position clears some
much-needed space for her growing legs and buttocks. Many babies now have a full
head of hair, with locks maybe around one inch / 2.5 centimeters long. But
don't be surprised if her hair isn't the same color as yours.
Dark-haired couples are sometimes taken aback when their children are born with
bright red or blond hair, and fair-haired couples likewise can produce babies
with dark hair. And then, of course, some babies don't have any hair at all..
The coating of lanugo that covered your baby from 26 weeks has disappeared, and
so has most of the vernix caseosa, the whitish substance that also covers her.
Your baby will continue to develop about a half an ounce of fat a day, and is
getting rounder and pinker. She is still practicing breathing, in preparation
for life outside the womb.
The 38th week
Your baby can measure anywhere from 19 inches to 21 inches. Your baby
weighs about 6 pounds, 6 ounces by now. Fat is still accumulating, although
growth is slower now. Since your baby has had the muscles to suck and swallow
amniotic fluid, waste material has been accumulating in his or her intestines.
Cells shed from the intestines, dead skin cells, and lanugo hair are some of the
waste products that contribute to meconium, a greenish-black substance that
constitutes your baby's first bowel movement. Your baby is now full term,
which means that if your baby were born today, he or she would be considered a
full-grown baby. Your baby is still growing an ounce a day at 38 weeks pregnant.
The 39th week
Your baby is likely between 19.5 and 21.5 inches long from head to
toe and may weigh around 7 pounds. While your baby has very little room to move
around if you notice absence of movement completely, call your doctor or midwife
immediately. The placenta will continue to supply your baby with antibodies..
These antibodies will help your baby fight infection the first 6 months to 12
months of life. The umbilical cord that carried nutrients from the placenta to
your baby is now 20 inches long and half an inch thick. By now your baby’s arm
and leg muscles are quite strong. All of your baby’s organs are fully
functional. Your baby’s lungs are getting stronger in preparation for life
outside the womb.
The 40th week
By the beginning of this trimester your baby will be building fat
stores and muscle mass. Your baby's hair will be growing, replacing the
lanugo that protected her skin in the womb. By the end of this trimester your
baby will be approximately 7 pounds in weight and about 20 inches long. Your
baby's lungs mature right up to birth. If you haven't packed your
hospital bag, now is the time to do it
