Week by week - Baby growth

Care For All

Week by week - Baby growth

The average length of pregnancy (gestation) is counted as 40 weeks but, the unborn baby spends around 38 weeks in the womb, the reason for this is because pregnancy is not counted from the date of conception but from the first day of the woman’s last period, which occurs two weeks later generally.

Pregnancy is divided into three trimesters:

  • First trimester – conception to 12 weeks
  • Second trimester – 12 to 28 weeks
  • Third trimester – 29 to 40 weeks.


At the stage of conception inherited characteristics and gender are decided in. Conception is the moment when the woman’s ovum (egg) is fertilized by the man’s sperm.

Week 1

Your baby hasn’t been conceived in this week, but still, it is part of your 40-week pregnancy. This first week is actually mother’s menstrual period. Because the expected birthdate (EDD or EDB) is calculated from the first day of your last period.

Week 2

At the end of this week fertilization of women’s egg by the sperm will take place.

Week 3

After conception thirty hours later, the cell splits into two. After three days, the cell (zygote) is divided into 16 cells. Two more days later, the zygote has moved to the uterus (womb) from the fallopian tube. Seven days later to conception, the zygote inserts itself into the plump uterine lining (endometrium). The zygote is now called as a blastocyst. A part of blastocyst becomes placenta and produces hCG (human chorionic gonadotropin) that supports pregnancy. Important organs like brain, spinal cord, heart start developing in this week. The baby is of the size of head of a pin.

Week 4

The baby that is developing in this week is tinier than a grain of rice. The process of forming the various body systems is done by the rapidly dividing cells, including the digestive system.

Week 5

The baby looks more like a tadpole at this stage. Your baby’s heart is beating at a steady rhythm. Eyes and ears are forming.

Week 6

The baby is about ¾ of an inch in length. Development of nose, jaw, palate and lungs have begun. The hand and feet have web-like structures that will become fingers and toes. Most of the pregnancies are diagnosed by this stage because of missed menstrual period and urine pregnancy tests.

Week 7

At this stage, every important organ has begun to form in the tiny body. The hair, eyelids and tongue have begun developing. The baby’s placenta is burrowing into the uterine wall of mother to access oxygen and nutrients from her bloodstream.

Week 8

Now the embryo is little over an inch in length, approximately as much as a bean. The head is disproportionately large. Baby’s facial features continue to mature. Bones start to form, muscles start contracting.

Week 9

In this week baby is as big as a grape. The embryo’s liver starts to produce blood cells. The embryo starts to move all the joints like knee, elbow, shoulder. Your baby may start making a fist.

Week 10

The embryo from this week is known as a fetus and is about 2.5 cm in length. The formation of all bodily organs will be done. Your baby’s head comprises half the length of the body. Nails and hair are visible. The baby is actively swallowing and kicking legs.

Week 11

The little heart is evolving further and the teeth are hiding inside the gums. Skin is still transparent. Your baby is 21/2 inches long.

Week 12

Your baby begins to take more recognisable appearance. Kidneys now secrete urine. Brain continues to mature. This week marks the end of first trimester, baby is around 3 inches long and weighs 1 ounce.

Week 13

The fetus is now more than 7 cm in length and can swim around quite vigorously. Baby develops unique fingerprints. Baby’s skin is covered by fine soft hair called lanugo.

Week 14

Now the baby can mutely cry since it has vocal cords. The eyes are fully developed but the eyelids are fused. The baby may start sucking its thumb. Nails start growing from fingers and toes. The baby may even start to grimace, frown and squint.

Week 15-16-17

In this stage fetus is about 14 cm in length and weighs 21/2 ounces. The tongue has taste buds and the eyelashes and eyebrows have appeared. The baby’s skin is very thin and the blood vessels can be seen through the skin. Your baby is preparing for a growth spurt.

Week 18-19-20

A protective covering called myelin starts forming around the baby’s nerves. Surprisingly, hiccoughs in the fetus can often be observed during ultrasound scans. Congratulations on making it half-way through your pregnancy.

Week 21

The fetus now is about 21 cm in length. The ears can hear muffled sounds from the outside world and are fully functioning. Now with an ultrasound scan, the genitals can be distinguished. You must have most likely felt your baby’s movements by now.

Week 22 & 23

Baby starts to look like a miniature new-born. The belly that is increasing in size may seem like a hand-magnet. Baby will be able to feel your movement.

Week 24

The fetus is around 28-36 cm in length. The closed eyelids now separate into lower and upper lids, allowing the baby to open and shut its eyes. The baby starts to make breathing movements with its lungs.

Week 25

Baby’s body hair starts growing and she even starts to put on weight. This will help your baby look less wrinkeled.

Week 26 & 27

Your baby starts to practice breathing by inhaling and exhaling small amounts of amniotic fluids. You can appreciate the baby movements well. Your baby also has developed a regular wake and sleep cycle.

Week 28

Your baby now weighs around 1 kg (1,000 gm) and measures about 25 cm (10 inches) from head to down. The head-to-toe length is around 37 cm.

Week 29

There is substantial growth in your baby’s muscles and lungs. The head is growing giving space to the developing brain.

Week 30

Now your baby weighs nearly 3 pounds and you start to experience mood swings, clumsiness, and fatigue. The baby’s eyes can now identify difference between light and darkness.

Week 31

You start to experience sleepless nights due to the strong kicks of your baby.

Week 32

You start to have problems with breathing and heatburn because of your growing uterus as your baby is plumping.

Week 33

In this week baby starts to weigh close to 4 pounds and because of this you start to toddle and you feel uncomfortable in bed.

Week 34

You start to have dizziness and fatigue. The baby’s central nervous system starts to mature in this stage.

Week 35

The baby is comfortable and well protected in the womb that she is not able to do somersaults but you can experience subtle movements of the baby.

Week 36

Your baby’s weight increases by one ounce every day. You can start to feel the movement of your baby inside your womb.

Week 37

In this week you may have occasional contractions and vaginal discharge. Your baby’s brain and lungs continue to grow.

Week 38

You need to see in case if there are any symptoms of preeclampsia. Baby has a firm grasp in this stage and you can prepare to meet your baby soon.

Week 39

This is the one but final week of your pregnancy and your baby is fit and ready to meet the outside world. In case your water breaks inform your doctor immediately.

Week 40

The baby is about 51 cm in length. It is mostly a combination of physical, hormonal and emotional factors between the mother and baby. Now the baby is ready to be born.