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40 Weeks Pregnant: Baby Development

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  • Week 1 begins on the first day of your last period, so technically you’re not pregnant yet. Healthcare providers use this way to get an accurate estimation of the due date.

  • Preconception stage.

  • The uterine lining is being shed in the form of blood. After that, your body begins preparing to release the next egg. 

References:

Pregnancy Symptoms Week 1: Early and First Week Symptoms & Signs of Pregnancy

Before Missing Period – PregaJunction

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  • Week 2 is when the eggs are ready to be released and fertilized by the sperm.

  • You can become pregnant when you copulate during ovulation late in week 2 (also called the Fertile window).

 

 

 

 

References:

Fetal development: The 1st trimester - Mayo Clinic

Baby and You at 2 Weeks Pregnant: Symptoms and Development

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  • Sperms travel to the fallopian tubes (where the egg is present) to fertilize it. Once fertilized, an egg and a sperm form a zygote.

  • This zygote travels from the fallopian tube into the uterus. As it travels, the zygote multiplies its cells to form a small ball of cells.

  • You may have several zygotes under the following circumstances:

    • a. More than one egg is released and fertilized;

    • b. One fertilized egg is separated into two.

 

References:

Implantation and Establishment of Pregnancy in Human and Nonhuman Primates - PMC

Fertilization and implantation - Mayo Clinic
Fetal development: The 1st trimester - Mayo Clinic 

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  • Once in the uterus, the zygote which has now developed into a blastocyst implants itself into the lining of the uterus. 

  • Blastocyst refers to a ball of cells with two layers. The inner layer of cells develops into the embryo; the outer layer of cells protects and aids in the nourishment of the developing embryo.

 

 

References:

Fetal development: The 1st trimester - Mayo 

How Big Is My Baby This Week? Here's a Baby Fruit Size Chart (parents.com)Clinic  

Blastocyst - Mayo Clinic  

Implantation and Establishment of Pregnancy in Human and Nonhuman Primates - PMC

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  • The embryo continues to develop by dividing its cells to form more. These cells form three different layers.

    • Ectoderm (outer layer)→ develops into the outer layer of skin, nervous system, eyes, and ears;

    • Mesoderm (middle layer) → develops into the heart and circulatory system; also is the base for the formation of bones, ligaments, kidney, and part of the reproductive system; 

    • Endoderm (innermost layer)→  develops into the lungs and intestines.

 

References:

Fetal development: The 1st trimester - Mayo Clinic 

5 Weeks Pregnant | Pregnancy | Start for Life (www.nhs.uk)

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  • The organs of the baby begin to form.

  • The arms also begin to grow.  

  • The neural tube begins to develop into the brain and spinal cord. 

  • The embryo takes on a “c-shape”. 

 

References:

Fetal development: The 1st trimester - Mayo Clinic 

How Big Is My Baby This Week? Here's a Baby Fruit Size Chart (parents.com)

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  • The brain continues to develop.

  • The hands that began to sprout in week six begin to look like the webbed feet of birds as the fingers begin to develop. 

  • Small limbs that develop into legs also begin to appear.

  • Small dents that eventually develop into nostrils appear.

  • Retina begins to form as well. 

 

 

References:

Fetal development: The 1st trimester - Mayo Clinic 

7 Weeks Pregnant | Pregnancy | Start for Life (www.nhs.uk)

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  • The baby’s limbs begin to become more distinct. 

  • Fingers begin to form. 

  • Ears and eyes become more apparent.

  • The nose and upper lip have formed.

  • The “C-curve” becomes less clear as the neck and torso begin to straighten slightly. 

  • A network of nerves begins to develop throughout the body. 

 

 

References:

Fetal development: The 1st trimester - Mayo Clinic  

How Big Is My Baby This Week? Here's a Baby Fruit Size Chart (parents.com)

When does the brain develop? | BabyCenter

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  • The baby’s arms are more distinct as the elbows develop.

  • The toes on the legs are also more clear-cut. 

  • The appearance of eyelids. 

 

 

References:

Fetal development: The 1st trimester - Mayo Clinic

How Big Is My Baby This Week? Here's a Baby Fruit Size Chart (parents.com)

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  • The baby’s head takes on a visibly round shape.

  • The fingers and toes become more clear-cut defined as the webbing goes away.

  • Eyes and ears continue to develop. 

  • The baby has brain waves and the heart is beating at about 180 beats per minute.

  • The baby has internal sex organs.

 

 

References:

Fetal development: The 1st trimester - Mayo Clinic 

https://www.pregnancybirthbaby.org.au/pregnancy-at-week-10

10 Weeks Pregnant | Pregnancy | Start for Life

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  • The baby is now a fetus. 

  • The body continues to develop (eyes, eyelids, ears, and other organs).

  • Buds that develop into future teeth appear. 

  • The baby’s genitals begin to form, based on the sex chromosome pair  (XX– girl, XY– boy). 

 

 

References:

Fetal development: The 1st trimester - Mayo Clinic 

11 Weeks Pregnant: Symptoms and Baby Development | Pampers

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  • The baby’s face has taken on a more recognizable appearance.   

  • The baby also begins to develop fingernails. 

  • Kidneys can secret urine.

  • May develop more complicated reflexes such as sucking. 

 

 

References:

Pregnancy Week 12 - 12 Weeks Pregnant 

Fetal development: The 1st trimester - Mayo Clinic 

12 weeks pregnant: baby's development, scans and telling people about your pregnancy | Tommy's (tommys.org)

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  • Movement of baby’s intestines from the umbilical cord into the abdomen.

  • Baby’s head is now ⅓ of the body.

  • The kidneys and urinary tract are functional.

  • Continuous development of facial features and the baby’s head can now move.

  • A layer of fine hair (lanugo) covering the fetus’s skin starts to grow. 

  • Baby weight is at more or less  25 grams (0.88 ounces).

 

 

References:

Pregnancy: 13 - 16 weeks (news-medical.net) 

13 Weeks Pregnant | American Pregnancy Association

13 Weeks Pregnant | Pregnancy | Start for Life

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  • Arms are at almost full length.

  • The neck is better defined and eyebrows are formed.

  • Some babies may begin to suck their thumb.

  • The baby can swallow amniotic fluids and the kidneys have started working and producing urine.

  • The ovarian follicles start forming (if a baby is female) or the prostate starts to appear (if a baby is male).

  • Baby weight is 40 grams (1.41 ounces)

References:

healthy-pregnancy-guide.pdf (canada.ca)

Pregnancy: 13 - 16 weeks (news-medical.net)

14 Weeks Pregnant: Baby Development, Symptoms & Signs

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  • The baby’s bones are hardening and the muscles are developing.

  • Their short legs are now growing longer every day.

  • They develop hearing abilities though their eyes are still closed.

  • The baby weighs 70 grams (2.47 ounces).

 

 

 

References:

15 weeks pregnant: fetal development - BabyCenter Canada
Your Guide to a Healthy Pregnancy - Canada.ca

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  • The circulatory system is fully functional.

  • The heart is able to pump 24 liters of blood daily.

  • Baby’s head is more upright.

  • The baby is about to have a 3-week growth spurt.

  • The nervous system continues to develop, and the baby starts moving its arms and legs.

  • The baby may start punching around inside you. 

  • Development of baby’s scalp pattern. 

  • Baby weight is 100 grams (3.53 ounces)

 

References:

16 weeks pregnant: fetal development - BabyCenter Canada

16 Weeks Pregnant | Pregnancy | Start for Life

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  • Hearing keeps developing, and the baby can start to hear your voice.

  • The development of unique patterns of fingerprints and toeprints. 

  • Fat stores begin to form under the baby’s skin.

  • Skeleton continues to harden.

  • Weight of 140 grams (4.94 ounces).

 

 

References:

17 weeks pregnant: fetal development - BabyCenter Canada

17 Weeks Pregnant: Baby Development, Symptoms & Signs

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  • Mid-pregnancy ultrasound scan can be done this week.

  • In the case of a girl, the uterus is in place, and her vagina and fallopian tubes are continuously growing. 

  • In the case of a boy, his penis will be distinct. 

  • The main branching tubes in the lungs start to form tinier tubes.

  • Can respond to sound.

  • Myelin (a protective layer of covering) starts to form around the nerves.

  • The baby is 190 grams (6.7 ounces)

References:

18 weeks pregnant: fetal development - BabyCenter Canada

Your Guide to a Healthy Pregnancy - Canada.ca

Pregnancy Week 18

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  • The brain forms specific areas for all 5 senses (smell, taste, hearing, vision, and touch).

  • Hairs start to grow out of the scalp.

  • A white protective coating called vernix caseosa appears on the baby’s skin. 

  • Teeth begin to grow.

  • Main airways in the lungs (bronchioles) start to form.

  • The baby weighs 240 grams (8.47 ounces)

 

References:

19 weeks pregnant: fetal development - BabyCenter Canada

19 Weeks Pregnant | Pregnancy | Start for Life

https://www.whattoexpect.com/pregnancy/week-by-week/week-19.aspx

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  • Baby’s movement is like butterflies or gas bubbles.

  • The first flutters you feel are called ‘quickening’ if this is your first pregnancy.

  • Plenty of growing room, and the baby is able to stretch and flex. 

  • Baby’s regular activities include thumb-sucking and winking of his/her eyes. 

  • Baby weighs 300 grams (10.58 ounces). 

  • The first poop can be seen in the intestines.

References:

BBC-7th-edition-FINAL-Nov2019.pdf (gov.bc.ca)

Week 20 of Pregnancy: What's Going On Inside | HealthLink BC 

20 Weeks Pregnant | Pregnancy | Start for Life

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  • Able to make facial expressions.

  • Their transparent skin gradually turns from pink to red.

  • The liver and the spleen have been working hard to produce more blood cells

  • Baby’s movements are more coordinated.

  • Baby can swallow small amounts of amniotic fluid.

  • 360 grams (12.7 ounces) of weight

References:

21 weeks pregnant: fetal development - BabyCenter Canada

21 Weeks Pregnant: Baby Development, Symptoms & Signs

Fetal development: MedlinePlus Medical Encyclopedia

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  • Head and body hair called lanugo thickly covers the baby.

  • Eyes have developed and irises are not fully pigmented.

  • The baby is able to clear excess water in its body by peeing.

  • Lower limbs are fully developed.

  • Mammary glands which are responsible for making breast milk continue to grow for a baby girl. 

  • For a baby boy, testes start to descend from his pelvis into the scrotum, and they usually reach the scrotum in the third trimester. 

  • The baby is 430 grams (15.17 ounces) of weight

References:

22 weeks pregnant: fetal development - BabyCenter Canada

fetal.pdf (sd.gov)

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  • Baby starts to have rapid eye movements.

  • Fingerprints and footprints begin to form.

  • Baby is more sensitive to sounds, and may respond to certain sounds.

  • Baby’s heart beats a little stronger.

  • Skin starts to appear red.

  • Weighing more than 500 grams (1.1 pounds).

References:

23 weeks pregnant: fetal development - BabyCenter Canada

Fetal development: The 2nd trimester - Mayo Clinic

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  • Lungs are developed enough and the baby is now considered viable (if born at this stage, with intensive medical care, the baby has a 60%-70% chance of survival).

  • Sleeping and waking up patterns are more defined.

  • The bigger they become, the stronger punch you may feel.

  • The rapid growth of the brain.

  • Skin is wrinkled and red.

  • Weighs 600 grams (1.32 pounds)

References:

BBC-7th-edition-FINAL-Nov2019.pdf (gov.bc.ca)

24 weeks pregnant: fetal development - BabyCenter Canada

When Is It Safe to Deliver Your Baby? | University of Utah Health.

fetal.pdf (sd.gov)

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  • Wrinkled skin starts looking smooth as that of a newborn.

  • Scalp hair growth continues.

  • Baby’s startle reflexes are developing 

  • Eyelids are separating. 

  • Nostrils and nose start to work by ‘breathing’ amniotic fluid.

  • Rapid eye movement (REM) occurs throughout most of the baby’s sleep time even though the eyelids are closed.

  • Baby vigorously responds to touch and sound. 

  • The baby’s weight is about 660 grams (1.46 pounds)

 

References:

pregnancy book complete march 2019.pdf (hscni.net)

25 weeks pregnant: fetal development - BabyCenter Canada

www.whattoexpect.com/pregnancy/week-by-week/week-25.aspx

Fetal development: The 2nd trimester - Mayo Clinic

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  • An 85% chance of survival if the baby is born at this time in a hospital with high-risk newborn professionals.

  • Baby might distinguish the different voices of the mother and her partner.

  • Baby’s eyelids open for the first time.

  • Full development of taste buds.

  • 760 grams (1.68 pounds) of weight

 

References:

26 weeks pregnant: fetal development - BabyCenter Canada

fetal.pdf (sd.gov)

pregnancy book complete march 2019.pdf (hscni.net)

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  • Formation of eyelashes.

  • The nervous system continues to mature.

  • Baby keeps changing their position in the uterus.

  • The baby is putting on weight and fat continuously. 

  • Baby might have hiccups.

  • Weight of about 875 grams (1.93 pounds)

References:

Embryonic & Fetal Development (scdhec.gov)

Fetal development: The 2nd trimester - Mayo Clinic

27 Weeks Pregnant | Pregnancy | Start for Life

27 Weeks Pregnant: Baby Development, Symptoms & Signs

27 Weeks Pregnant: Symptoms and Baby Development | Pampers

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  • This week is the beginning of the third trimester.

  • The baby’s central nervous system (CNS) can now orchestrate paced breathing and control body temperature.

  • Baby moves around to respond to bright lights. 

  • The baby’s heart rate is 140 beats per minute (bpm). 

  • The senses of hearing, smell, taste, and touch are developed and functional. 

  • Weighs around 1kg (2.2 pounds). 

References:

Fetal development: The 3rd trimester - Mayo Clinic

28 Weeks Pregnant | Pregnancy | Start for Life (www.nhs.uk)

When does the brain develop? | BabyCenter

How Big Is My Baby This Week? Here's a Baby Fruit Size Chart

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  • The baby may begin to kick and make other movements. 

  • The baby can tell the difference between bright sunlight and artificial light through the uterine wall.

  • Baby’s first smile may appear, especially during sleep.

  • The baby had more hiccups.

  • Skin becomes smoother as more fat begins to build up.

  • The baby weighs 1.13kg-1.36kg (2.5 to 3 pounds)

References:

Fetal development: The 3rd trimester - Mayo Clinic

Your Pregnancy Week by Week: Weeks 26-30 (webmd.com)

29 Weeks Pregnant: Baby Development, Symptoms & Signs

How Big Is My Baby This Week? Here's a Baby Fruit Size Chart

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  • Eyes open wide.  

  • Formation of red blood cells in the bone marrow.   

  • Thicker hair on the head.

  • You may experience ‘false’ labor contractions called  Braxton Hicks.

  • Baby is most likely in the head-down position and will descend further into your pelvis in the following weeks.

  • The baby weighs around 1.32 kg (2.9 pounds).

 

References:

Fetal development: The 3rd trimester - Mayo Clinic

30 Weeks Pregnant: Symptoms, Tips, and More (healthline.com)

Baby and You at 30 Weeks Pregnant: Symptoms and Development

30 Weeks Pregnant: Ultrasound, Symptoms, Baby Development

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  • Most organ development is complete. 

  • Rapid weight gain. 

  • Skin continues to thicken. 

  • The brain is more sophisticated, and brain connections between nerve cells are growing rapidly.    

  • The brain can process information and can detect signals from the five senses.

  • Can determine familiar sounds and voices. 

  • The baby weighs about 1.5kg (3.31 pounds)

 

References:

Your Pregnancy Week by Week: Weeks 31-34 (webmd.com)

31 Weeks Pregnant | Pregnancy | Start for Life

31 Weeks Pregnant: Baby Development, Symptoms & Signs

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  • Visible toenails.  

  • The fine hairs covering the baby’s skin (lanugo) start to shed. 

  • Most babies are positioned head-down (also called cephalic presentation) in the 32nd and 36th week. 

  • Baby continues to gain weight, and may take up most space in the uterus 

  • Weighs around 1.7 kg (3.75 pounds)

 

References:

Your Pregnancy Week by Week: Weeks 31-34 (webmd.com)

Fetal development: The 3rd trimester - Mayo Clinic

Fetal Positions for Birth.

32 Weeks Pregnant: Symptoms and Baby Development | Pampers

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  • The pupils can change size to detect changes in light.

  • The brain and nervous system are completely developed. 

  • Hardening of bones, except the skull. 

  • Weighs around 1.92 kg  (4.23pounds)

 

References:

31 Weeks Pregnant | Pregnancy | Start for Life (www.nhs.uk)

Fetal development: The 3rd trimester - Mayo Clinic

How Big Is My Baby This Week? Here's a Baby Fruit Size Chart

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  • There is not a lot of space for the baby to move. The baby is curled up in the uterus in a head-down position. 

  • Fingernails grow long enough to reach the tips.

  • Skin is pink. 

  • The fat build-up continues. 

  • The baby weighs about 2.1kg (4.6 pounds)

References:

Embryonic & Fetal Development (scdhec.gov)

34 Weeks Pregnant | Pregnancy | Start for Life (www.nhs.uk)

Fetal development: The 3rd trimester - Mayo Clinic

Your Pregnancy Week by Week: Weeks 31-34

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  • Continued accumulation of fat under skin, and the baby looks chubby. This keeps baby warm after birth. 

  • Weighs around 2.4kg (5.3 pounds)

 

 

 

 

References:

35 Weeks Pregnant | Pregnancy | Start for Life (www.nhs.uk)

How Big Is My Baby This Week? Here's a Baby Fruit Size Chart

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  • The baby takes up much of the space in the amniotic sac.

  • It’s harder for the baby to move, but the Mom should still be able to feel some movement.

  • Baby’s skull bones are not joined together to comparatively easily go through the birth canal. 

  • Lungs are properly developed by now, and the baby can breathe after birth. 

  • Weighs about 2.63kg (5.8 pounds)

References:

36 Weeks Pregnant | Pregnancy | Start for Life (www.nhs.uk)

Embryonic & Fetal Development (scdhec.gov)

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  • Baby has a firm grasp.  

  • The head might begin turning towards the pelvis. 

  • Babe is getting ready to come out

  • Weighs about 2.9kg (6.3 pounds).

 

References:

Fetal development: The 3rd trimester - Mayo Clinic

37 Weeks Pregnant | Pregnancy | Start for Life (www.nhs.uk)

37 Weeks Pregnant: Week by Week Pregnancy | Mom365

37 weeks pregnant: Your baby is now as big as a stalk of swiss chard

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  • Most of the lanugo is shed (except for shoulders and upper arms) 

  • The baby is not having any significant development, and the baby has taken on his/her final birth appearance. 

  • The baby begins to store meconium in the bowels (Meconium are contents from the womb; excreted out after birth).

  • The baby weighs about 3.08 kg (6.8 pounds)  

References:

38 Weeks Pregnant | Pregnancy | Start for Life

Hey, Week 38 of pregnancy? Here's everything you need to know about the baby and you!

Average fetal length and weight chart - BabyCenter Canada

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  • The baby’s skin has changed from pink to white.

  • The firmly formed layer of skin aids with survival after birth (to protect internal organs and control body temperature).

  • The baby weighs about 3.29 kg (7.25 pounds)

 

References:

39 Weeks Pregnant | Pregnancy | Start for Life (www.nhs.uk)

Fetal development: The 3rd trimester - Mayo Clinic

Average fetal length and weight chart - BabyCenter Canada

39 Weeks Pregnant: Baby Development, Symptoms & Signs

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  • The baby is fully developed and ready to come out. 

  • There is barely any space for the baby to move. 

  • Weighs about 3.5 kg (7.63 pounds)

 

 

 

References:

40 Weeks Pregnant | Pregnancy | Start for Life (www.nhs.uk)

Average fetal length and weight chart - BabyCenter Canada

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