week-by-week, pregnancy, pregnancy week by week, fetal development

First Trimester

Pregnancy Week 1

Pregnancy Week 1 begins with your menstrual bleeding or period. You are not pregnant yet. Cycle day 1 is the first day of menstrual bleeding.  Ovulation and fertilization happen at the end of next week.
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menstrual period and cycle

Pregnancy Week 2

Technically, you are not pregnant yet in pregnancy week 2. But you should be aware of typical fertility and ovulation symptoms and you need to have sex regularly if you want to improve your chances of getting pregnant. At the end of pregnancy week 2, ovulation happens and the sperm meets the egg on the day of ovulation in a process called fertilization. 
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pregnancy week 2 fertilization


Pregnancy Week 3

pregnancy week 3

Pregnancy week 3 is technically your first week that you are pregnant, when ovulation and fertilization happen, and when the fertilized egg moves down through the fallopian tube towards the uterus. Implantation happens on average 9 days after ovulation/fertilization.

embryo inside fallopian tube pregnancy week 4

Pregnancy Week 4

Week 4 is a very eventful week. This is when pregnancy actually begins when the embryo implants on average 9 days after fertilization/implantation, about 6-12 days after ovulation/fertilization. During pregnancy week 4 the embryo will have concluded the travel through the fallopian tube, arrive in the uterus and implant on average 9 days after fertilization/ovulation. And within days after implantation, the pregnancy test will be positive!

Pregnancy fetus 5 weeks

Pregnancy Week 5

Now things are moving along quickly in the growth process. The blastocyst now consists of three layers. The innermost layer or endoderm is where the intestine, bladder, pancreas, and liver will form.

pregnancy fetus week 6

Pregnancy Week 6

The heart has now started beating and can often be seen early in the 6th week by transvaginal ultrasound. Baby is now about 1/17 of an inch in length and growing rapidly.  

pregnancy  fetus week 7

Pregnancy Week 7

Your baby has grown from 1/17 of an inch to 1/3 of an inch. While your baby may still be very small, many of the crucial organs are developing rapidly. Arms and legs are growing, but fingers and toes have yet to sprout. 

pregnancy fetus week 8

Pregnancy Week 8

You are now more than halfway through the first trimester, and the baby continues to grow rapidly. Last week, baby measured 1/3 of an inch and now he has grown to 3/4 of an inch in length. The heart is beating and if an ultrasound is performed, a fluttering will be seen on screen.


pregnancy fetus week 9

Pregnancy Week 9

Cartilage is now forming and bones are growing. Baby is forming the skeleton that he will use to stand, walk and run later in life. Eye structure is progressing and the tongue is beginning to develop. Intestines have formed in the umbilical cord, but are now moving out of the cord and into baby’s abdomen. 

pregnancy fetus week 10

Pregnancy Week 10

Growth has reached a crucial point by week 10 and you may see fetal movements on ultrasound. The movements are very small, but they are quite important. With joints fully developed, baby needs to move to ensure everything is working properly. 

pregnancy fetus week 11

Pregnancy Week 11

At the start of the 11th week, the baby is now officially called a fetus. The most crucial development phases are concluding. The fetus now must concentrate on growing longer and larger during the next 29 weeks. Growth is fast now and the fetus will gain about one inch in length during the 11th week alone. 

pregnancy fetus week 12

Pregnancy Week 12

The 12th week starts a new day for the fetus. Growth speed is increasing exponentially and formed organs are starting to practice the functions they will have outside of the womb. The intestines, for example, start practicing peristalsis. Peristalsis is the muscle movement of the intestines that helps during digestion. 

pregnancy fetus week 13

Pregnancy Week 13

The 13th week concludes the first trimester. The alien look of an early fetus on ultrasound is disappearing as the eyes move closer together and the ears shift to their normal location. The gender could be viewed if an ultrasound could see that far into the womb.

Second Trimester

pregnancy fetus week 14

Week 14
Welcome to your 2nd trimester of pregnancy! At this point in growth, an ultrasound would show movement in the chest area. This movement is breathing practice. Hands and feet are moving now too, though most of the movements are reflex. 

pregnancy fetus week 15 

Week 15
By the 15th week of pregnancy, some parents are itching to find out the sex of the baby. In utero, the fetus may be sucking the thumb or fingers. The suck reflex is one of the most important instincts a baby has because, without the suck reflex, babies cannot breastfeed or bottle feed effectively. 

pregnancy fetus week 16

Week 16
By the start of the 4th month, pregnant women tend to start feeling movements in the abdomen. Initially, it may only feel like flutters but the fetal bones are hardening now so movements that have been occurring for weeks can now be felt. 

pregnancy week 17

Week 17
The fetus is continuing to grow faster than ever before.  All reflexes are in place so the fetus can suck, swallow and blink. The heart is pumping vigorously and can pump more than 25 quarts of blood on any given day.

 pregnancy fetus week 18

Week 18
Bowel development continues and the first bowel movement, meconium, is developing inside. Baby will not pass the first movement until after birth, in most cases. The fingers and toes are developing pads and soon fingerprints will form. The boy fetus is developing the prostate gland during week 18 of pregnancy.

pregnancy fetus week 19 

Week 19
Lanugo, or fine hair, has been growing on baby’s skin since the 15th to 16th week. During week 19, vernix caseosa starts to develop. Vernix caseosa is a thin white covering that protects the skin from the fluid environment of the amniotic sac. 

pregnancy fetus week 20

Week 20
The 20th week marks the halfway point for a normal pregnancy. Growth continues to add length and weigh to the baby. By the 20th week, baby can weigh more than one pound and measure 8 inches or longer. Fetal growth is determined by many factors, so the baby may grow more quickly for some pregnant women and more slowly for others.

pregnancy fetus week 21

Week 21
This week marks a slight slowing of the growth process. The fetus continues to grow, but more attention is paid to internal organs and development than weight gain. Length does not slow as rapidly, so the fetus may take on an extremely thin façade for a while. Male fetuses begin to drop the testes during week 21.  

pregnant woman week 22

Week 22
The fetal brain growth continues daily. The sense of smell, taste, sight, hearing, and touch are all developing as well. Baby can suck, swallow and hear. What is the fetus hearing? Heartbeats, breathing, and digestion. These sounds are like lullabies to the baby, which may be why babies tend to be more comfortable laying on mom’s tummy than dad’s tummy for a while after birth.

pregnancy fetus week 23 

Week 23
This week marks a huge milestone for the fetus. Development has reached the point that the fetus could conceivably survive if an early birth was required. The risk factors for impaired neonatal health are high, and survival, though very low, is a tangible reality. Baby will sleep and wake, though maybe not on the same cycle as mom.

pregnancy fetus week 24

Week 24
Now the fetus is usually considered "viable" in the U.S. by most doctors. That means it has a reasonable chance of surviving if born prematurely. During the 24th week, the fetus continues to gain good weight. Weighing in at more than 1 1/3 pounds, your baby is gaining weight thanks to bone development, muscle growth, and organ growth. 

pregnancy fetus week 25

Week 25
The spine continues to strengthen in the 25th week of pregnancy. When complete, the spine will be made up of 1000 ligaments, 150 joints, and 33 rings. The process seems complicated, but the female body has all the instructions down pat. Lungs also continue to grow with blood vessel winding through lung tissue. The nostrils have been closed to this point, but now they start to open just a bit.

pregnancy fetus week 26

Week 26
The fetus continues to grow rapidly and weighs about two pounds and measures nine inches or more by the 26th pregnancy week. The air sacs of the lungs are starting to develop and the surfactant is being secreted to line the air sacs. A surfactant is necessary for normal lung function. The brain is also working hard as hearing and vision are developing this week.

pregnancy fetus week 27

Week 27
This is another huge landmark in pregnancy. It is the last week of the second trimester. The baby's brain is quickly developing and the lungs continue to prepare for breathing air once the baby is born. Eyelids open and retinas develop this week as well.

Third Trimester

 pregnant woman week 28

Week 28
Welcome to your 3rd trimester! The 28th week of gestation is the start of the 7th month and the third trimester. The fetus is growing by leaps and bounds and has a 90% chance of survival if born during this week. The lungs can breathe air, though some development is still needed to fully function properly outside the womb. Body fat increases to 2-3% this week. Your baby can weigh more than two pounds by the end of the week.

pregnancy fetus 29 weeks

Week 29 
The fetus is finally starting to look like a baby. The head and body are proportionate at this time. Weight gain is rapid as fat stores continue to build under the skin. Eyes are completely developed and are now sensitive to light. Fetuses are now able to hear, see and smell. Women that are pregnant with multiples have the same milestones this week though singlets may soon outweigh multiples.

pregnancy fetus 30 weeks 

Week 30 
Fetal growth continues and the baby weighs three pounds or more and continues to gain weight daily. Bones have developed and bone marrow has started producing red blood cells. The white covering over the skin, lanugo, is starting to fade away in preparation for birth. Hearing has developed to the point that the fetus recognizes certain voices. Both mom and dad can talk to baby, sing and laugh. These sounds do not have to be directed at the belly for baby to hear.

pregnancy fetus 31 weeks 

Week 31 
Fetal growth is beginning to slow down a bit. As space tightens, the baby develops at a slower rate. All necessary body functions are working perfectly, the time spent in the uterus at this point is all about lung development and weight gain.

pregnant woman week 32

Week 32 
All five senses are now in full working order. The fetus can see, taste, smell, feel and hear. Hair continues to grow, though some babies will be born with much more than others. Weight gain slows down a bit, especially for women pregnant with multiples. Between weeks 32 and 40, multiple fetuses will steadily gain less weight than singlets.

pregnancy fetus 33 weeks

Week 33 
Amniotic fluid levels reach an all-time high. Fluid levels will remain the same until the baby is born. Fetal skin starts out red, but changes to pink in the latter weeks of pregnancy. The color change is attributed to fat distributions under the skin. More fat means pinker skin.

pregnancy fetus 34 weeks

Week 34 
Brain development is rapid and thus the size of the head is growing to hold new brain tissue. Brain development accounts for the growth of about 3/8 of an inch each week. 

pregnancy fetus 35 weeks 

Week 35
The fetus weighs in at more than 5 ½ pounds by the 35th week. This number is just an average as some babies are born full term weighing only 5 1/2 pounds. There is very little room left in the uterus, so when baby moves the pregnant woman will feel it. It is common to visibly see movement through the skin of the abdomen from time to time including kicking, punching and rolling. 

pregnant woman week 36

Week 36 
It's just four weeks to go until the due date. During the next few weeks, the weight of the baby will shift downward relieving some of the shortness of breath associated with the upward growth of the uterus. While this can leave a pregnant woman feeling as if she has enough wind to run a marathon, the relief comes at a price. That marathon will be run to and from the bathroom. The downshift in weight leaves very little space for storage in the bladder. The baby continues to collect fat with dimpling starting on knees and elbows.

pregnancy fetus week 37

Week 37
The 37th and 38th weeks of pregnancy are considered early term. Pregnant women who make it to the 37th week no longer have to worry about delivering the baby early. The fetus weighs around 6 1/2 pounds and practices breathing during every waking moment. An ultrasound will actually show fetal breathing movements which often confuses parents. Baby is not really breathing, as there is no air in the uterus.

pregnant woman 38 weeks

Week 38
If baby measures too large at an ultrasound in the 38th week, the doctor may choose to induce labor to protect the health of the pregnant woman and baby. Meconium is also developing in the bowel of the fetus. When the bag of waters breaks, it should be clear. If meconium appears in the amniotic fluid,  you will be monitored more closely and labor will be sped along as quickly as possible.

pregnancy newborn baby 39 weeks

Week 39
Good things come to those who wait. And if you are scheduled for a cesarean section, either because you previously had a cesarean section or for other reasons, chances are that it will be done in the 39th or 40th pregnancy week or later.

pregnancy newborn 40 weeks

Week 40 
Time is up! With 40 weeks of the pregnancy behind you, many pregnant women feel the time to have the baby is NOW! Predicting birth dates is an inexact science. There is a give of two weeks before and after the estimated date of birth. A pregnancy is not considered overdue until after the 42nd week. Rest assured, however, the baby is now fully-grown and ready to safely exist outside the womb.

pregnancy baby 41 weeks

Week 41
By now, most pregnant women are ready to give birth. Fatigue, pain, swelling and abdominal weight alone are enough to keep women in bed until labor pains begin. For the fetus, week 41 is nothing more than an extended vacation. The fetus will continue to store fat and practice breathing throughout the 41st week. As long as the placenta is in good working order and amniotic fluid levels are good, the baby is fine.

pregnancy 42 weeks baby

Week 42
In most pregnancies, the baby will have been born by the 42nd pregnancy week. With every passing day, the chance of having a vaginal birth diminishes, especially for pregnant women with narrow hips. If the baby has not moved into the birth canal, C-section may be the best option. 

Read More:
Labor, Delivery, and Birth Guide
Labor Contractions Timer Tool