This is a project on gestation period for class 12 biology investigatory project

1. Week4
Baby (called an embryo) consists of two layers of cells
— the epiblast and the hypoblast — that will eventually
develop into all of baby's organs and body parts. Two
other structures that develop at this time are the
amnion and the yolk sac. The amnion, filled with
amniotic fluid, will surround and protect the growing
embryo. The yolk sac will produce blood and help to
nourish the embryo until the placenta takes over that
role.
Week5
The neural tube, which will eventually form into the
spinal cord and brain, runs from the top to the bottom
of the embryo. A bulge in the centre of the embryo will
develop into baby's heart. At this time, the placenta
develops. It is through the placenta and its finger like
projections, called chorionic villi, that an embryo
receives nourishment from its mother.
Week6
Baby’s brain and nervous system are developing at a
rapid pace. Optic vesicles, which later form the eyes,
begin to develop this week on the sides of the head, as
do the passagewaysthat will make up the inner ear.
Baby's heart will begin to beat around this time, and it
may even be detected on ultrasound examination. And

2. the beginnings of the digestive and respiratory systems
are forming, too. Small buds that will grow into baby's
arms and legs also appear in this week. Baby only
measures 0.08 to 0.2 inches (2 to 5 millimeters) from
crown to rump.
Week7
Baby is constantly adapting to life inside the uterus. The
umbilical cord has formed. It will be baby’s connection
to mother throughout the pregnancy, providing oxygen
and nourishment for the baby and disposing of baby's
wastes. In addition, baby's digestive tract and lungs
continue to form. Baby's face is taking shape. The
mouth, nostrils, ears, and eyes are some of the facial
features that become more defined this week. The arm
bud that developed just last week has a hand on the
end of it.
Week8
The fingers and toes are just beginning to form this
week, and the arms can even flex at the elbows and
wrists. The eyes are becoming more obvious because
they’ve begun to develop pigment in the retina. Also,
the intestines are getting longer and there isn’t enough
room for them in the baby’s abdomen, so they protrude
into the umbilical cord until week 12.By now, the

3. beginnings of the buds that will develop into baby's
genitals have made their appearance.
Week9
The tail at the bottom of baby's spinal cord has shrunk
and almost disappeared by this week. In contrast,
baby's head has been growing — it's quite large
compared with the rest of the body and it curves onto
the chest. By this week, baby measures about 0.6 to 0.7
inches (16 to 18 millimeters) from crown to rump and
weighs around 0.1 ounces (3 grams). The tip of the nose
has developed and can be seen in profile, and flaps of
skin over the eyes have begun to shape into eyelids.
The digestive system continues to develop. The anus is
forming, and the intestines are growing longer. In
addition, internal reproductive features, such as testes
and ovaries, start to form this week. Baby may make
some first movements this week as muscles develop.
Week10
All of baby's vital organs have been formed and are
starting to work together. 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 baby is a boy, his testes will
begin producing the male hormone testosterone.

4. Congenital abnormalities are unlikely to develop after
week 10. This also marks the end of the embryonic
period — in general, the embryo now has a distinctly
human appearance and starting next week baby will
officially be considered a fetus.
Week11
From this week until week 20, baby will be growing
rapidly — increasing in size from about 2 inches (5 cm)
to about 8 inches (20 cm) from crown to rump. To
accommodate all this growth, the blood vessels in the
placenta are increasing in both size and number to
provide the baby with more nutrients. Facial
development continues as the ears move toward their
final position on the sides of the head. The baby's head
accounts for about half of the body length. Baby's
reproductive organs are developing rapidly, the
external genitals of boys and girls appear somewhat
similar until the end of week 11.
Week12
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 first trimester. Baby's kidneys
are functioning. After swallowing amniotic fluid, baby
will now be able to pass it out of the body as urine. And

5. the intestines will make their way into the abdomen,
since there is room for them now.
Week13
At beginning of the second trimester of pregnancy,
placenta has developed and is providing baby with
oxygen, nutrients, and waste disposal. The placenta also
produces the hormones progesterone and estrogen,
which help to maintain the pregnancy. By now, the
baby's eyelids have fused together to protect the eyes
as they develop.
Week14
By this week, some fine hairs have developed on baby's
face. This soft colourless hair is called lanugo, and it will
eventually cover most of baby's body until it is shed just
before delivery. By now, baby's genitals have fully
developed, though they may still be difficult to detect
on an ultrasound examination. In addition, baby starts
to produce thyroid hormones because the thyroid gland
has matured. Baby now weighs about 1.6 ounces (45
grams) and is about 3.5 inches (9 cm) long from crown
to rump.
Week15

6. Baby’s skin has been continuously developing, and it is
so thin and translucent that we can see the blood
vessels through it. Hair growth continues on the
eyebrows and the head. Baby's ears are almost in
position now, although they are still set a bit low on the
head. Internally, Baby's skeletal system continues to
develop. Muscle development continues too, and baby
is probably making lots of movements with her head,
mouth, arms, wrists, hands, legs, and feet.
Week16
Baby now weighs about 3.9 ounces (110 grams) and
measures about 4.7 inches (12 cm) in length from
crown to rump. Baby can hold her head erect, and the
development of facial muscles allows for a variety of
expressions, such as squinting and frowning.
Week17
At about 5.1 inches (13 cm) from crown to rump and
weighing 4.9 ounces (140 grams), baby is still very tiny.
The placenta, which nourishes the fetus with nutrients
and oxygen and removes wastes, is growing to
accommodate baby. It now contains thousands of blood
vessels that bring nutrients and oxygen from mother’s
body to baby's developing body.

7. Week18
Ears move to their final position and they stand out
from the head. The bones of the middle ear and the
nerve endings from the brain are developing so that
baby will hear sounds such as heartbeat and blood
moving through the umbilical cord. She may even be
startled by loud noises. Baby's eyes are also developing
— they're now facing forward rather than to the sides,
and the retinas may be able to detect the beam of a
flashlight. Until now, Baby's bones had been developing
but were still soft. This week, they begin to harden, or
ossify. Some of the first bones to ossify are those in the
clavicles and the legs.
Week19
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. Baby is still tiny, but this
week brings the development of brown fat, which will
help keep the baby warm after birth. During the last
trimester, baby will add more layers of fat for warmth
and protection.

8. Week20
Baby now weighs about 11 ounces (312 grams) and
measures about 6.3 inches (16 cm) from crown to
rump. The baby is taking up increasing room in the
uterus, and continued growth will put pressure on
mother’s lungs, stomach, bladder, and kidneys. Under
the vernix caseosa, baby's skin is thickening and
developing layers. Hair and nail growth continue.
Week21
The amniotic fluid that has cushioned and supported
the baby in the uterus now serves another purpose. The
intestines have developed enough that small amounts
of sugars can be absorbed from the fluid that is
swallowed and passed through the digestive system to
the large bowel. Almost all of the baby's nourishment,
however, still comes from mother through the placenta.
Until now baby's liver and spleen have been responsible
for the production of blood cells. But now the bone
marrow spaces are developed enough to contribute to
blood cell formation as well, and bone marrow will
become the major site of blood cell production in the
third trimester and after birth. (The spleen will stop
producing blood cells by week 30, and the liver will stop
a few weeks before birth.)
Week22

9. Taste buds have started to form on the tongue, and the
brain and nerve endings are formed enough so that the
fetus can feel touch. Baby may experiment with this
newfound sense of touch by stroking her face
or sucking on a thumb, as well as feeling other body
parts and seeing how they move. Baby's reproductive
system is continuing to develop, too. In boys, the testes
have begun to descend from the abdomen, and in girls,
the uterus and ovaries are in place and the vagina is
developed.
Week23
Even though fat is beginning to accumulate on baby's
body, the skin still hangs loosely, giving baby a wrinkled
appearance. Baby's daily workout routine includes
moving the muscles in the fingers, toes, arms, and legs
regularly. By now baby weighs a little more than 1
pound (454 grams). If preterm labor and delivery were
to occur this week, a baby could survive with
expert medical care, but might have mild to severe
disabilities.
Week24
Baby is still receiving oxygen through the placenta. But
once birth occurs, her lungs will start taking in oxygen
on their own. In preparation for that, baby's lungs are

10. developing the ability to produce surfactant. Surfactant
is a substance that keeps the air sacs in our lungs from
collapsing and sticking together when we exhale,
allowing us to breathe properly. Because the inner ear
— which controls balance in the body — is now
completely developed, baby may be able to tell when
she is upside down or right side up while floating and
making movements in the amniotic fluid.
Week25
Baby has resting and alert periods. Fetal activity is more
readily when mother is more sedentary. Baby's hearing
has continued to develop, too —she may now be able
to hear voice.
Week26
Although baby's eyes have been sealed shut for the last
few months, they will soon open and begin to blink.
Depending on ethnicity, some babies will be born with
blue or gray-blue eyes (which may change color in the
first year of life) and some will be born with brown or
dark eyes. Eyelashes are growing in, as is more hair on
the head. Baby, weighing a little less than 2 pounds

11. (907 grams), still looks wrinkly but will continue to gain
weight steadily over the next 14 weeks until birth.
Week27
By this first week of the third trimester, baby looks
similar to what she will look like at birth, except thinner
and smaller. The lungs, liver, and immune system still
need to fully mature, but if born now, baby would have
a very good chance of surviving. As hearing continues to
develop, baby may start to recognize voice. Sounds may
be muffled, though, because the ears are still covered
with vernix, the thick waxy coating that protects the
skin from becoming chapped by the amniotic fluid.
Week28
Baby now weighs about 2 pounds, 2 ounces (1,000
grams) and measures about 10 inches (25 cm) from
crown to rump. Babies who are in the breech position
may need to be delivered by cesarean section. Baby still
has 2 months to change position. Most babies will
switch positions on their own. The folds and grooves of
baby's brain continue to develop and expand. In
addition, baby continues to add layers of fat and has
continued hair growth.
Week29

12. Baby continues to be active, and starts first few flutters
of movement like hard jabs and punches. Baby should
move at least 10 times in two hours. If baby moves less,
talk to health care provider.
Week30
Now weighing about 3 pounds (1,400 grams) and
measuring about 10.8 inches (27 cm) from crown to
rump, baby continues to gain weight and layers of fat.
This fat makes the baby look less wrinkly and will help
provide warmth after birth. In preparation for
respiration after birth, baby will mimic breathing
movements by repeatedly moving the diaphragm. Baby
can even get the hiccups, which can be felt as rhythmic
twitches in the uterus.
Week31
By now baby is urinating approximately several cups of
urine a day into the amniotic fluid. She is also
swallowing amniotic fluid, which is completely replaced
several times a day. Excess fluid in the amniotic sac
(known as polyhydramnios) may mean that the baby
isn't swallowing normally or that there is a
gastrointestinalobstruction. Inadequatefluid in the
amniotic sac (oligohydramnios)may mean that the
baby isn't urinating properly and could indicate a
problem with the kidneys or urinary tract.

13. Week32
Eyelashes, eyebrows, and the hair on baby's head are
evident. The lanugo hair that has covered your baby
since the beginning of the second trimester is falling off,
althoughsome may remain on the shoulders and back
at birth. At about 4 pounds (1,800 grams) and 11.4
inches (29 cm) from crown to rump, baby would have
an excellent chance of survival outside the womb if
delivered now.
Week33
In these last few weeks before delivery, the billions of
developed neurons in baby's brain are helping her to
learn about the in-utero environment — baby can
listen, feel, and even see somewhat. Baby’s eyes can
detect light and the pupils can constrict and dilate in
response to light. Like a newborn, baby sleeps much of
the time and even experiences the rapid eye movement
(REM) stage. Baby's lungs are almost completely
matured. Fat will continue to be deposited on baby's
body for protection and warmth. Babies gain a good
deal of their weight in the final few weeks before birth.
Week34

14. Maternal calcium intake is extremely important during
pregnancy because the baby will draw calcium from the
mother to make and harden bone. If a pregnant woman
doesn't get enough calcium during pregnancy, it can
affect her own bones because the developing fetus will
take minerals from the mother's skeletal structure as
needed. The vernix coating on the baby's skin is
becoming thicker, whereas lanugo hair is almost
completely gone. By now most babies will be in position
for delivery. Babies born at 34 weeks usually have fairly
well-developed lungs, and their average size of 5
pounds (2,250 grams) and 12.6 inches (32 cm) from
crown to rump allows them to survive outside the
womb without extensive medical intervention.
Week35
Baby already weighs about 5 pounds, 5 ounces (2,400
grams), but this week begins baby's most rapid period
of weight gain — about 8 to 12 ounces (226 to 340
grams) each week. Fat is being deposited all over baby's
body, especially around the shoulders. Because of this
increasing size baby is now cramped and restricted
inside the uterus — so fetal movements may decrease,
but they may be stronger and more forceful. If baby is
in a headfirst position, her head will rest on mother’s
pubic bone in preparation for labor.
Week36

15. The wrinkly, tiny fetus seen on earlier ultrasounds has
given way to an almost plump baby. There is fat on
baby’s cheeks, and powerful sucking muscles also
contribute to baby's full face. Baby now weighs a little
under 6 pounds (2,721 grams).The bones that make up
baby’s skull can move relative to one another and
overlap each other while baby’s head is inside mother’s
pelvis. This phenomenon is called molding, and it helps
the baby pass through the birth canal.
Week37
By now, baby has developed enough coordination to
grasp with the fingers. If shown a bright light, baby may
turn toward it in the uterus. She continues to gain
weight — developing fat at the rate of half an ounce (14
grams) a day. In general, boys weigh more than girls at
birth.
Week38
Baby weighs about 6 pounds, 6 ounces (2,900 grams) by
now and measures about 13.4 inches (34 cm) in length
from crown to rump. Fat is still accumulating, although
growth is slower now. Weight gain has decreased or
ceased. Since baby has had the muscles to suck and
swallow amniotic fluid, waste material has been

16. accumulating in 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 baby's first
bowel movement. If it is a boy, his testicles have
descended into the scrotum. If it is a girl, the labia are
now completely developed.
Week39
Umbilical cords, which carry nutrients from the
placenta to the baby, vary in size but average about 22
inches (55 cm) long and half an inch (1-2 cm) thick.
Sometimes the umbilical cord can become wrapped
around a baby’s neck. Generally, this doesn’t cause
problems, althougha cesarean delivery could be
required if it causes pressure on the umbilical cord
during labor or delivery. A true knot in the umbilical
cord is much less common, occurring in only about 1%
of pregnancies. Most of the vernix that covered baby's
skin has disappeared, as has the lanugo. Mother’s body
has been supplying the baby with antibodies through
the placenta that will help the baby's immune system
fight infection for the first 6-12 months of life.
Week40
After many weeks of anticipationand preparation, baby
is here. Or maybe not — only 5% of women deliver on

17. their estimated due dates, and many first-time
mothers find themselves waiting up to 2 weeks after
their due date for their baby to arrive. A baby born at
40 weeks weighs, on average, about 7 pounds, 4 ounces
(3,300 grams) and measures about 20 inches (51 cm).
Newborns often have heads temporarily misshapen
from the birth canal and may be covered with vernix
and blood. Baby's skin may have skin discolorations, dry
patches, and rashes — these many variations are
completely normal.