Stages of Fetal Development Week by Week

Congratulations! Your family of two is soon going to become a family of three. The journey from the day of conception to holding your baby in your arms for the first time is priceless and full of memories. There is a lot to look forward to and be prepared for; however, watching your baby grow is a magical feeling of its own.

This article takes you through the highlights of your prenatal development and stages of fetal development journey through every trimester and week. Keep reading to find out more.

Early-stage of pregnancy

When you are in your early stage of being pregnant, you may not be sure about your due date or how far along you are. It is important to bear in mind that you might not even suspect that you are pregnant in the first few weeks after you conceive. The first and the most common sign that signifies that you are pregnant is a missed period.

Every pregnancy and fetal development milestones is monitored over three major trimesters. Each of these three month periods makes up the full term of nine months of your pregnancy.

Most doctors measure the trimesters in weeks, which is how we have broken down the pregnancy calendar into week-on-week fetal developmental progress below for you read to on.

Fetal Development: First Trimester

This is the beginning of your pregnancy, which is also popularly known as the first trimester. During this stage of fetal development, your little one will grow from a microscopic cluster of cells to a plum-sized fetus. In the first trimester, your baby will also start to develop facial features that may start to look a little like his parents.

Highlights of fetal development: Week 1 to 3

  • The last day of your menstrual cycle will be the day your pregnancy “starts”. This means that your doctor will track your due date from the first day of your last period.

  • While you may not feel very different, week two is the most fertile time for you, as you are ovulating. If a fertilized egg attaches itself to the wall of your uterus you may experience light spotting. This may look like you are on your period, but is a sign of conceiving.

  • Week three is when the zygote has been formed, this zygote will multiply in the coming weeks to form the organs and body of your little baby.

  • The placenta will begin to form. The placenta helps nourish the baby and keep him healthy.

Highlights of fetal development: Week 4

  • The egg has now fertilized and implanted itself in the uterus. It begins to develop into an embryo in week 4.

  • Your baby will now be visible in the ultrasound. He will be faintly visible as he is barely the size of a poppy seed.

  • The umbilical cord starts to form from the placenta.

    Fetal Development: Week 4

Highlights of fetal development: Week 5

There is major fetal development by week 5. Your baby starts to,

  • The neural tube, which is the tube via which your little ones prime organs start to form. This comprises the brain, spinal cord, and backbone.

  • The lungs and heart of your little one also begin to start forming. You may be able to hear a faint heartbeat in the ultrasound between weeks 6-12.

  • The amniotic sac has fully formed and is filling with amniotic fluid in week 5. This fluid will help protect your little one for the next 35 weeks.

  • The signs of pregnancy will start to show more prominently. You will experience morning sickness, sore breasts, and the frequent need to pee.

  • If you haven’t confirmed that you are pregnant already, this might be the right time to book an appointment or take a pregnancy test at home.

  • The embryo is now the size of an orange seed.

Fetal Development: Week 5

Highlights of fetal development: Week 6

  • Your little one is now ½ inch long and the embryo is huddled up in a curved ‘C’ shape.

  • Your little one may still look like a tadpole, but it isn’t going to be too long before human features start to show. Your baby is slowly starting to develop organs that will help him breathe and eat in a few months.

  • Your embryo is now the size of a pomegranate seed.

    Fetal Development: Week 6

Highlights of fetal development: Week 7

Your little one is growing so quickly! In fetal development by week 7 your little one will,

  • Eyelids and bones start to form.

  • Your little one's brain and face start to grow.

  • Retinas and nostrils begin to develop.

  • Your embryo is attached to the umbilical cord, which provides your baby with the nutrition it needs in the womb.

  • Your embryo is now the size of a blueberry.

    Fetal Development: Week 7

Highlights of fetal development: Week 8

Your baby is developing rapidly! Baby development in the womb by week 8 is,

  • The building blocks of your baby are in place. All the major organs have started to develop. They include - the heart, kidneys, liver, lungs, and intestines.

  • Tubes connect the throat with the lungs to allow breathing in the future.

  • Your baby is no longer an embryo, he is now a fetus as per medical terms.

  • Your fetus is now the size of a raspberry and has started to develop the beginning facial features. His body has also started to straighten out.

Fetal Development: Week 8

Highlights of fetal development: Week 9

  • Your baby’s head is larger in proportion to his body at this stage. However, in the coming weeks, this will even out as your baby starts to develop bodily organs.

  • Your baby’s tadpole-like tail is almost gone and in its place legs have started to form.

  • Your fetus is now the size of a cherry.

    Fetal Development: Week 9

Highlights of fetal development: Week 10

  • Your baby is getting ready to see and hear you! Your little one’s eyes and ears continue to develop through fetal development by week 10.

  • The head of your baby has started rounding out.

  • The fetus is now the size of a strawberry.

    Fetal Development: Week 10

Highlights of fetal development: Week 11

The rapid growth of your baby is super exciting! By week 11 your baby will,

  • Your baby measures around 2 inches from head to rump. Most of this is his head, however, this proportion will even out in the coming weeks.

  • Muscle formation has begun.

  • The production of red blood cells has begun in the liver.

  • The backbone is soft, but other bones start to harden.

  • Your fetus is about the size of a brussel sprout by week 11!

    Fetal Development: Week 11

Highlights of fetal development: Week 12

Your little one has started to move, but you won’t feel it just yet.

  • The arms and hands of your baby have developed more than his lower limbs.

  • Facial features start to get more defined. He may have your chin or your partner’s nose.

  • If you have a Doppler exam this week, you may be able to hear a heartbeat.

  • The fetus is about the size of a passion fruit by week 12.

    Fetal Development: Week 12

Fetal Development: Second Trimester

You’ve completed the first trimester! Your baby will be arriving in roughly 27 weeks. Another good news is that by the end of the first trimester, the risk of a miscarriage drops down significantly.

Highlights of fetal development: Week 13

  • The sex hormones, testosterone, and estrogen have started being produced.

  • Your little one will now start to produce urine after swallowing the amniotic fluid.

  • All the organs have been fully formed by week 13 and are rapidly growing.

  • The average fetus size is equal to the size of a large plum.

    Fetal Development: Week 13

Highlights of fetal development: Week 14

  • You will now start to put on some weight and the baby bump will start to slowly show.

  • Your baby will start to develop a sense of smell and taste.

  • Your baby’s fingers have started to develop fingerprints. He will also be able to move his hands to his mouth.

  • The neck and lower limbs of your baby have started to become more defined. The skin of your fetus has also started to thicken.

    Fetal Development: Week 14

Highlights of fetal development: Week 15

  • The fetus is now able to roll and flip.

  • Your baby’s tiny heart pumps up to 100 pints of blood every day.

  • Your fetus is now the size of a small grapefruit.

    Fetal Development: Week 15

Highlights of fetal development: Week 16

  • Your fetus can now hear sounds! This is the best time to start talking to your baby and communicating with him.

  • The digestive system of your baby starts to work.

  • Your little one will now be the size of an apple.

    Fetal Development: Week 16

Highlights of fetal development: Week 17

  • Your baby’s glands will start producing vernix by week 17. Vernix is a greasy substance that protects your little one’s skin in the womb.

  • Your baby’s eyes are now able to move. Toenails start to grow as well.

  • The fetus is now roughly the size of a pear.

    Fetal Development: Week 17

Highlights of fetal development: Week 18

  • Your baby’s skin has started to develop peach-like fuzz. This is called lanugo. Lanugo acts like a coat to keep your baby warm in the womb. There is no reason to worry though, the lanugo will be gone by your due date.

  • The fetus may wake up from his sleep as a response to your movements.

    Fetal Development: Week 18

Highlights of fetal development: Week 19

  • The baby develops reproductive organs. Ovaries are developed in girls and testes have formed in boys.

  • Your baby’s movements and kicks start to get stronger.

  • The fetus is now about the size of a mango.

    Fetal Development: Week 19

Highlights of fetal development: Week 20

  • Your baby starts to produce meconium. Meconium is the waste that will become your baby’s first poop after birth.

  • A few facial features and external genitals will start becoming visible in the ultrasound.

  • His fingernails have started growing.

  • The baby is the size of a bell pepper on average.

Fetal Development: Week 20

Highlights of fetal development: Week 21

  • You may feel rhythmic movements in your belly. This movement is your baby hiccupping.

  • Your baby has completely developed fingernails and toes.

  • The little one may have a favorite sleeping position.

  • Your baby is the same size as a banana.

    Fetal Development: Week 21

Highlights of fetal development: Week 22

  • Your baby’s earring power has become stronger. He may move around suddenly when he hears a loud noise.

  • Your baby is able to move his eyes for a few weeks now, but his eyelids are still fused shut.

  • Your baby’s eyebrows start to grow.

  • The little one is now the size of a papaya.

    Fetal Development: Week 22

Highlights of fetal development: Week 23

  • Your little one will spend most of his time in the rapid eye movement (REM) phase of sleep. The REM phase of sleep is when your brain is active which results in your baby having dreams.

  • The baby may respond to your voice by moving.

  • Your baby is now approximately the same size as an eggplant.

    Fetal Development: Week 23

Highlights of fetal development: Week 24

  • The lungs of your baby have formed, but are not functional yet. Fetal lung development is underway.

  • The skin of your baby is thin and wrinkled.

    Fetal Development: Week 24

Highlights of fetal development: Week 25

  • Your baby has started to gain weight. You’ll soon be able to squeeze those chubby cheeks!

  • Your little one’s nervous system is developing rapidly.

    Fetal Development: Week 25

Highlights of fetal development: Week 26

  • Fetal lung development continues as the lungs start producing surfactant to help them inflate properly.

  • Your little one starts to produce melanin. Melanin is the pigment that gives color to your skin.

  • Your baby is now about the same size as a zucchini.

    Fetal Development: Week 26

Highlights of fetal development: Week 27

  • The little muffin has started to move around more. Your baby has started to stretch and kick more often.

  • The baby can now make grasping motions.

  • Your baby finds your voice calming and soothing. Your baby’s heart rate may decrease when you talk or sing to him.

  • The baby is now the size of a cauliflower.

Fetal Development: Week 27

Fetal Development: Third Trimester

It’s time for the home stretch! Time has flown by and you are in your final trimester. Before you know it you will be heading to the hospital with your hospital bag, ready to welcome your tiny tot into this world. Here are the highlights of fetal development week by week in the third trimester:

Highlights of fetal development: Week 28

  • Your baby can now open and shut his eyes. He will also start to grow eyelashes around week 28.

  • Your baby's breathing has become more rhythmic.

Fetal Development: Week 28

Highlights of fetal development: Week 29 and 30

  • Your baby’s kicking and movement a more noticeable.

  • The fine hair, also known as lanugo will start to shed by week 30.

  • Your baby may have hair on his head.

  • Bone marrow starts to produce red blood cells, which help transport oxygen.

  • Your baby is now the same size as a cabbage.

Fetal Development: Week 29 and Week 30

Highlights of fetal development: Week 31 and 32

  • The bones of your baby begin to harden. The baby will also be able to regulate the temperature of his body.

  • Even though the bones have hardened, his skull is still soft and pliable. This won’t completely harden until the age of 2.

  • Your baby’s toenails may start to grow.

  • Your baby is now adding fat to his body. His skin will now become less transparent.

  • Your baby will now be the same size as a coconut.

    Fetal Development: Week 31 and Week 32

Highlights of fetal development: Week 33 and 34

  • Your baby will start to put on weight rapidly from this stage. He may put on around quarter kg every week until his birth.

  • The brain development of your baby continues and all his five senses are working.

  • Your baby will now start to shift his position and get ready for birth. He will start to move in the head-down position.

  • Your baby's fingernails continue to grow.

  • Your baby is now the same size as a pineapple.

    Fetal Development: Week 33 and Week 34

Highlights of fetal development: Week 35 and 36

  • As the fetal brain development continues, other parts of the lungs and the nervous system are also still developing.

  • The musculoskeletal system has fully developed to enable movement after birth.

  • Your baby is now starting to take up more space in the amniotic sac.

  • The little one now is the same size as a honeydew melon.

    Fetal Development: Week 35 and Week 36

Highlights of fetal development: Week 37 and 38

  • Your baby has added enough fat to his body to keep him warm after birth.

  • The baby is still growing and is considered early term.

  • Your baby’s liver and lung development are almost complete.

  • Your baby will begin to further drop in your pelvis.

  • The baby’s head and abdomen may be of the same circumference.

    Fetal Development: Week 37 and Week 38

Highlights of fetal development: Week 39 and 40

  • Your baby has officially grown full term!

  • Fetal brain development continues, and his brain will keep growing well into early childhood.

  • By week 40, your baby will be ready to be born.

  • The length of your baby will be between 18 to 20 inches.

  • An average newborn baby weighs around six to nine pounds i.e. around 3-4.5 kgs.

    Fetal Development: Week 39 and Week 40

40 weeks may seem like a long time to hold your little one in your arms, but they pass by very quickly. Once your baby is here, he is sure to be showered with love, kisses, and gifts!