Week by week brief description of fetal development during pregnancy.
|Week 1-3||First Month||First Trimester|
|During this stage, most women are not even aware that they are pregnant. At fertilization, the genetic sex of the embryo is determined, either male or female! At 2 to 3 hours after conception, the cells are beginning to divide and double and by the fifth day the embryo is made up of about 90 cells. By about the 6th day, the embryo has traveled to the uterus and is beginning to implant and form the support for the pregnancy. During the next few weeks, the placenta and the very early stages of development of the embryo are beginning to take place.|
|The baby is absolutely tiny at this stage, but during this week he or she will develop a heartbeat. This week also marks the beginning of development of the eyes, ears, and arms and legs. Your baby is about the size of a droplet of water!|
|Week 5||Second Month|
|This week the baby’s nose and lips are forming. His arms and legs are better defined and his hands are starting to develop. The earliest stages of a soft skeleton are growing! His heart is pumping blood and his brain is growing and dividing.|
|Your baby’s features are becoming more obvious now. Her fingers are more developed and her toes are forming! Other important tissues are developing too, such as the liver, blood cells, spinal cord, and tiny roots which will become the teeth! Your little baby is small enough to fit on your thumbnail this week.|
|Your baby is changing and growing rapidly now. His face is complete with eyelids and his stomach and kidneys are forming. Your baby’s brain is now able to start to send messages to the tiny muscles and nerves beneath his skin. Hold up a nickel – that is about how big he is this week!|
|Your tiny baby now has his or her own handprints and footprints etched in the skin. Your baby is now visibly either male or female. He weights about 1.5gms and is about 1 inch long. Her heart beats at about 40 to 80 beats per minute. Now that all of the internal and external parts are formed, the embryo becomes a fetus.|
|Week 9||Third Month|
|Heads, Shoulders, Knees, and Toes!!! Knees and Toes, Knees and Toes!! Your baby’s many features are well formed now! He can move his arms and wrists and even flex his new muscles! The soft skeletal cartilage is slowly turning to bone, but the spine is still soft. Even though you can’t feel it yet, your little baby is starting to move. Can you picture a large button? That is about how big he is this week!|
|The baby’s face now has a very human appearance and the lower body is developing quickly now. She has a tiny little nose and is beginning to develop tiny fingernails. Her eyelids will be shut for another few months and her arms are long enough to touch her face. If you are appropriate for or considering diagnostic testing in pregnancy such as the CVS or amniocentesis, you may wish to schedule an appointment with a genetic counselor around this week.|
|Exciting changes are happening this week. Your baby’s organs are beginning to function: the pancreas is making insulin and the kidneys can make urine (which will become the baby’s amniotic fluid). The liver and spleen are producing cells and the white blood cells are now present to help protect against disease. The baby is about the size of a butterfly.|
|Your baby can really move now! He can turn his head, kick his feet, and breathing motions begin. Your baby may suck his thumb as he kicks and floats, weightless in the amniotic fluid. A parse layer of hair is forming on the upper lip, eyebrows, and palms of the hands and the feet. The placenta is now functioning and acts as your baby’ lungs, kidneys, liver, digestive and immune system.|
|Week 13||Fourth Month||Second Trimester|
|Congratulations! You are in the second trimester. She is growling rapidly now! She will soon double her weight! Keep eating your healthy diet to help her be as healthy as possible! Reproductive changes are also happening. In boys, the prostate gland develops this week and in girls the ovaries are dropping from the abdomen into the pelvis. Within the next few weeks, your doctor may discuss testing options for the pregnancy. If you are under 35, you will be offered the maternal serum screen (often called the triple screen or quad screen). For moms who are over 35 or who have a high-risk pregnancy, you will be offered either the maternal serum screen or amniocentesis. Amniocentesis is a test that can detect chromosomal abnormalities, such as Down syndrome and other abnormalities such as spina bifida. These choices are all up to you! It may help to discuss your options with a genetic counselor.|
|The musculoskeletal and nervous systems are beginning to mature. The baby is beginning to control his own movements. He can hold his head up, and the development of facial muscles allows him to make a variety of expressions such as squinting and frowning. The skeleton continues to develop this week so keep drinking that milk! Calcium is so important for your baby’s healthy development! Guess what else?! If your baby is female, millions of eggs will form in her ovaries this week.|
|This week your baby will develop hair. Lanugo, fine hairs that grow over your baby’s
body and protect the skin, also grows this week and will continue growing until just
before delivery. Most of it will disappear just before birth. Your little one has hands
that can grasp and feet that can kick against the amniotic sac!
|By now, all organs and structures have been formed. It is time for your baby to
GROW! GROW! GROW! The baby is about 6 inches long and a perfect size to fit
in the palm of your hand.
|Week 17||Fifth Month|
|“Rock a Bye Baby!” Start practicing this song and other nursery rhyme
favorites, your baby’s hearing is beginning to develop! Your baby can start to hear your
voice, your heartbeat and even when your stomach growls!
|Around this time, you may be beginning to “look” pregnant. You may also feel gentle
flutters, like butterfly wings. This feeling is called “quickening.” As your baby grows
and gets stronger, these feelings will strengthen into twists, turns and kicks!
|Your baby has a sucking reflex and has noticed that his thumb can reach his mouth! Your
baby is also now able to swallow, and he or she may swallow up to a liter of amniotic
fluid throughout the day. Recent research indicates that your baby may already be able to
feel thirsty! The baby’s thirst may be responsible for the amount of fluid swallowed in
order to keep the protective amniotic fluid at a normal level.
|By now, your baby has his or her own schedule (which may or may not match yours)!
Your baby will take naps and wake and be calm or active at different points throughout
the day and night. Most likely, your baby is turning, and sucking, and swallowing, and
kicking and has his own favorite position in your uterus. Sometimes your baby even has
the hiccups! These may last only a short period of time or for an hour – you may sense
them. Don’t worry – they are not a cause for concern.
|Week 21||Sixth Month|
|By now, your baby weighs about one pound! She continues to grow and is even
developing sweat glands, small fat deposits and increased muscle tone!
|Your baby continues to develop fingernails and toenails! His eyes may reopen soon and
his bones are developing rapidly. Your doctor may even be able to begin to feel the
baby’s head through your belly. Your baby’s permanent teeth are beginning to develop
in the jaw. Maybe some day the tooth fairy will be visiting!
|Peek a boo! Your baby’s eyelids can open and shut! She also has fairly well developed
respiratory functions by now – amniotic fluid can move in and out of the lungs. Her skin
is still very thin and can appear to have a reddish glow – lots of blood vessels and
capillaries are close to the surface.
|Your baby is growing rapidly every day now! She weighs about 1 ½ pounds and may be
about 10 to 12 inches long! All of her organs and body systems are in place and
functioning as she continues to grow. Congratulate yourself on being such a good
mother; she is totally dependent on you for all of her nutrition and care!
|Week 25||Seventh Month||Third Trimester|
|Ready set go! Your baby is moving much more and you may be getting a few good kicks
during some of the more active times of day. Her lungs continue to develop in
anticipation of when they will breathe oxygen and not amniotic fluid.
|Although Mom is providing all of the critical support to the baby right now, she can
actually breathe, swallow and regulate her body temperature to a certain extent. If you
were to deliver right now, survival would be possible, but complications could occur.
The baby will have much greater chances for a healthy life the longer she can stay in the
|What is the hair like in your family? The baby now has lots of hair, depending on the
genes that tend to be in the family. Your baby’s weight is now likely to be over 2 pounds
and length over 14 inches long. In addition, a material called surfactant forms in the
lungs. This helps them to work on their own after the baby is born.
|At this point, your baby can see light and hear sound. Her brain continues to develop the
pathways for thinking, speaking, understanding, and memory. Your baby is now twothirds
the size that she will be when she is born. This might really start to make a
difference in the way you feel. Enjoy the extra attention and friendly wishes of strangers.
|Week 29||Eighth Month|
|Your baby’s internal organs are now totally developed. You may be surprised at how
strong your babies grasp is by now – her little fingers will tend to curl around anything
they touch. Keep taking such good care of yourself!
|Your baby’s senses continue develop. Her eyes can see and she may even have taste
preferences. Sweet is more likely to be her favorite than bitter. Her organs are in
working order and ready to go soon!
|Fat deposits are helping to fill out your baby’s skin. They will also be important for
keeping him healthy and warm when he experiences the quick temperature change at the
time of his birth.
|Boy, this baby is growing fast now! She might be about 3 ½ pounds and 14 to 16 inches
long. Most importantly for healthy survival, her lungs should be starting the process of
fully maturing. The “lanugo” (soft hair) and vernix (creamy substance on skin) are
|Week 33||Ninth Month to term|
|It feels like that little bundle of joy is moving around quite a bit, but his space is getting
limited! Your job now is to keep him healthy and growing. The rest of the pregnancy
will be mostly about weight gain for your little one. On average, he will gain about an
ounce a day or approximately half a pound per week. This weight will help insulate the
baby’s body and will provide nourishment after you deliver as your baby learns his new
method of eating.
|Your baby should still be very active. Hopefully, the baby will be moving into a “head
down” position. It is important to keep monitoring your baby’s activity and movement at
this point in the pregnancy. Changes in movement, especially a decrease in movement or
no movement could mean that your baby may be having problems. If you notice a
decrease in movement, call your doctor or The St. Elizabeth Medical Center Family Birth
Place right away so that further testing can be ordered.
|Your baby should have a healthy, working immune system by now. You passed on all
kinds of healthy antibodies and this will provide the baby with protection for the first 6
months of life. Antibodies against measles, mumps, rubella, whooping cough and scarlet
fever have been transferred to the baby and will protect him. After about 6 months, his
immune system will take over and work on its own.
|You are now preparing for the long awaited birth. It may be days or weeks and your baby
will most likely be between 6 and 10 pounds. Your baby is a masterpiece; every baby is
unique and wonderful. We know you can’t wait to meet your baby and that he or she
can’t wait to meet you. These last few weeks will be filled with last minute preparations,
but try not to be too busy. Your days will be much busier once your little bundle of joy