The process of fetal formation and development week by week

This is an automatically translated article.

The article is professionally consulted by Dr., Doctor Ngo Thi Uyen - Obstetrician and Gynecologist - Department of Obstetrics and Gynecology - Vinmec Nha Trang International General Hospital

Pregnancy and motherhood is a woman's sacred responsibility. From a fetus after 40 weeks of "brooding" to giving mother a small angel is an inspiring journey with sweat and tears. According to the World Health Organization (WHO), vaccination for pregnant women is an important step to prevent certain bacteria and viruses that cause illness for both mother and baby during 9 months and 10 days of pregnancy. Therefore, mothers also need to keep in mind the vaccines that need to be given before and during pregnancy.

Week 2: Conceive

This week, you just ovulated. The egg is fertilized within 12-24 hours after the sperm meets the egg. If all goes well, this simple biological event begins a series of increasingly complex processes that create a new person. Over the next several days, the fertilized egg will continue to divide into many cells as it travels down the fallopian tube, into the uterus and begins to penetrate the lining of the uterus.

Week 3: Nesting

Now nestled in the nutrient-rich lining of the uterus is a microscopic ball of hundreds of cells that multiply at lightning speed. This ball, called the blastocyst, has begun to produce the pregnancy hormone hCG, upon this signal the ovaries will stop releasing an egg.

The 4th week

Our ball is now officially called an embryo. It's been about 4 weeks since the first day of your last period, which is usually when your next period should appear. At this time, home pregnancy tests will give positive results. At this point, our little friend is only the size of a poppy seed.

Week 5

Although he looks more like a tadpole than a human, he is growing very fast. The circulatory system is starting to form and the little heart will start beating this week. Baby is only as big as a sesame seed at this week of pregnancy.

6th week

Your baby's nose, mouth and ears begin to take shape, and the intestines and brain also begin to develop. Baby is 4-7mm (about the size of a green pea).

Week 7

The little boy has doubled in size since last week, his tail is still there but will disappear soon. Tiny hands and feet that looked like oars were growing from growing arms and legs. At this time, the length from the head to the bottom of the baby is about 9-15mm (about the size of a peanut).

Week 8

The little one starts to move around, but mom can't feel it yet. Nerve cells begin to branch, forming the primitive nervous system. The respiratory tube begins to extend from the throat to the developing lungs. Her current size is from 16-22mm.

9th week

Your basic form is already formed, even with pretty little earlobes, but the road is still long. The fetal tail is gone. She weighs only a fraction of an ounce, but you're about to gain weight fast. Mom, she's as big as a grape (head-butt length 23-30mm).

10th week

Our little friend has completed the most important part of the development process. Your skin is still translucent, but your little hands and feet can be folded and stretched, and small details like nails have begun to take shape. She has a head-butt length of 31-40mm.

11th week

Our angel is almost fully formed. Even though mom can't feel it yet, she can kick her legs, stretch, and even hiccup because her diaphragm is developing. At this point, she has a head-butt length of 41-51mm.

12th week

This week your little reflexes begin: Your fingers will soon begin to flex and stretch, your toes will curl, and your mouth will make sucking movements. She'll feel it when you gently touch her belly - even though she can't feel your movements yet. Your baby has grown as big as a lemon!

13th week

This is the last week of the first trimester of pregnancy. Your tiny fingers now have fingerprints, veins and internal organs clearly visible through the skin. If you're carrying a girl, your baby's ovaries contain more than 2 million eggs.

Entering the second trimester: What to expect?

After the first trimester, miscarriages are less common. For many moms-to-be, early pregnancy symptoms like morning sickness and fatigue are gone. If you feel more energetic now and haven't exercised before, this is a good time to start a regular pregnancy exercise routine.

Week 14

Your small brain now has nerve impulses and she can also move her facial muscles. The kidneys are also working. You can even see her sucking her thumb on the ultrasound now! My baby is now as big as a lemon! (head-butt length about 87 mm).

15th week

Your baby's eyelids are still closed, but he can still perceive light. If the mother shines the light on her belly, the baby will avoid the light. This week's ultrasound will reveal your baby's sex. Baby is the size of an apple this week.

Week 16

Your baby's scalp is starting to take shape, although no hair is visible yet. The small legs have now developed, when the mother can feel the fetus. Your little head is now straighter, and your ears are close to the correct position. Our little friend is now about the size of an avocado.

17th week

Our little one can now move his joints, and his skeleton - formerly soft cartilage - is now ossifying. The umbilical cord is getting stronger and thicker.
Mom's baby is the size of a radish.

Week 18

Baby is stretching his arms and legs, and mom can feel these lovely movements. Inside, a protective layer of myelin is forming around your nerve.
This week your baby weighs about 190 grams!

19th week

Your baby's senses - smell, sight, touch, taste and hearing - are developing and he can hear your mother's voice. You can talk, sing or read aloud to your baby if you like.
Your baby weighs about 240 grams.

20th week

Your baby can now swallow and her digestive system is making the sticky, dark, sticky meconium she will give on the first defecation - in a diaper or in the womb when you have a bowel movement. born.
Your baby is now the size of a banana, weighing about 300 grams.

Week 21

Baby's movements have changed from flapping wings to kicking or kicking the wall of your uterus. You can start paying attention to the poses as you get used to the baby's activities.
Your baby is the size of a carrot, about 360 grams.

22nd week

Our baby now looks like a miniature newborn. Features like lips and eyebrows are more pronounced, but the pigment that would color her eyes hasn't appeared yet.
Your baby weighs 430 grams.

23rd week

Baby's ears are getting better and better at picking up sounds. Even after birth, your baby may recognize some of the noises she now hears inside the uterus.
Your little friend is the size of a large mango, about 500 grams.

24th week

Our little friend has a rather long and thin figure, but the time to be chubby is coming. Your skin is still thin and translucent, but that will start to change soon, too.
Our little friend is as big as a cob of corn, about 600 grams.

Week 25

Baby's wrinkled skin begins to be filled with fat, making him look more like a newborn. Your baby's hair is starting to grow in color and texture.
Your baby now weighs about 660 grams.

26th week

Your baby is now inhaling and exhaling amniotic fluid, which helps with lung development. These breathing movements are the practice for the first breath of air at birth.
Your baby weighs about 760 grams.

27th week

This is the last week of your second trimester of pregnancy. Dear little one now sleeps and wakes up on a regular schedule, and your brain is very active. Your lungs aren't fully formed yet, but they can function outside of the uterus with medical help.
Mom's little friend is about 875 grams.

Third trimester of pregnancy: What's going to happen?

During the third trimester, you may urinate more often or experience leg cramps when your baby presses on nerves in your hips and back.
The honeymoon phase of pregnancy is over and the bliss of parenthood is looming on the horizon. Now is the time to do things like sign up for birthing classes, visit the doctor more often, and create a baby registry.

28th week

Your baby's eyesight is developing, this allows him to perceive light from outside through the filter. She can blink, and your eyelashes are already grown.
Your baby weighs about 1000 grams.

29th week

Your baby's muscles and lungs are busy getting ready for the outside world, and his head is growing to make room for his developing brain.
Your baby is the size of a pumpkin.
From week 29 to week 34, babies gain an average of 200g per week

30th week

Your baby is surrounded by half a liter of amniotic fluid, although the amount of amniotic fluid will become less as he grows and takes up more space inside your uterus.

31st week

Now our little one can wiggle his pretty head. A protective layer of fat is being accumulated under the skin and filling the small arms and legs.

32nd week

Mom will probably gain half a kilogram every week. Half of that weight goes directly to the little one, who will gain from one-third to one-half of her birth weight over the next seven weeks to prepare for life outside.

33rd week

The baby's skull bones have not yet been fused but are connected by cartilage tissue, which makes it easier for the baby's head to pass through the birth canal, they will not fuse completely until the baby is an adult.

34th week

Your baby's central nervous system and lungs are maturing. Babies born between 34 and 37 weeks with no other health problems can usually live normal long lives.
The average baby weight is about 2100 grams
From week 34 to week 40, your baby's weight increases on average about 200-250 grams per week.

Week 35

This place is getting more and more crowded, mom! Your baby's kidneys are fully developed, and the liver is also able to process some waste products.

36th week

Your little one is gaining about 30 grams per day. You are also losing the smooth membrane that surrounds your body along with the toxins and waxes that have protected you from the beginning until now

37th week

Mom's due date is fast approaching, but even though she looks like a newborn baby, she is not ready to enter the new world. Over the next two weeks, your baby's lungs and brain will fully mature.

Week 38

Are you curious about your baby's eye color? Your baby's irises aren't pigmented yet, so if your baby is born with blue eyes, they'll change color until they're about 1 year old.

Full term pregnancy

At 39 weeks, your baby will be considered full term. In the illustration, you can see how the mucus plug that seals your uterus and internal organs is pinched.

39th week

Baby has fully developed physically, but you are still busy storing fat to help regulate body temperature when going out into the world.

Week 40

If your due date has passed, it will not be as late as you think, especially if you calculate your due date based on the first day of your last period. Sometimes women ovulate later than expected.
But if you don't have any signs of labor on your due date, your doctor will do some tests like ultrasound and non-stress testing to make sure you can continue the pregnancy safely.
The average birth weight of a South Asian infant between 38-40 weeks is about 3200 grams - 3300 grams.

Week 41

At present, the mother's pregnancy is called the old-term pregnancy. More than 2 weeks from the due date is creating the risk of complications for mother and baby, the doctor will definitely advise the mother to perform induction.

See fetal development week by week in detail at:

Labor and birth

Seeing your baby for the first time is wonderful, but exactly what will lead to that moment is unpredictable, and it's natural for moms to feel anxious. Please consult your doctor and visit during pregnancy to ensure the health of mother and baby are always best protected.
During pregnancy, the mother may encounter a number of diseases if she does not have a proper diet, rest and regular antenatal check-up: Gestational diabetes, thyroid diseases, pre-eclampsia , high blood pressure,... These are all dangerous diseases and are difficult to detect if not tested and checked for pregnancy health. To protect the health of mother and baby during pregnancy, Vinmec offers all-inclusive Maternity packages.
Mother and baby will receive comprehensive care: before, during and after birth. Mother will be performed health check-ups, especially thyroid screening, Rubella test; Testing for parasites transmitted from mother to child. The baby will be screened before birth and after birth to help screen for abnormal diseases and birth defects right from the womb. In particular, at Vinmec, doctors will analyze the results and provide genetic counseling for prenatal screening for babies.

Please dial HOTLINE for more information or register for an appointment HERE. Download MyVinmec app to make appointments faster and to manage your bookings easily.