​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.
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Preconception stage.
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The uterine lining is being shed in the form of blood. After that, your body begins preparing to release the next egg.
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References:
Pregnancy Symptoms Week 1: Early and First Week Symptoms & Signs of Pregnancy
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Week 2 is when the eggs are ready to be released and fertilized by the sperm.
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You can become pregnant when you copulate during ovulation late in week 2 (also called the Fertile window).
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References:
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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.
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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.
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You may have several zygotes under the following circumstances:
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a. More than one egg is released and fertilized;
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b. One fertilized egg is separated into two.
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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.
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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
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.
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Ectoderm (outer layer)→ develops into the outer layer of skin, nervous system, eyes, and ears;
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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;
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Endoderm (innermost layer)→ develops into the lungs and intestines.
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References:
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The organs of the baby begin to form.
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The arms also begin to grow.
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The neural tube begins to develop into the brain and spinal cord.
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The embryo takes on a “c-shape”.
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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.
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The hands that began to sprout in week six begin to look like the webbed feet of birds as the fingers begin to develop.
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Small limbs that develop into legs also begin to appear.
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Small dents that eventually develop into nostrils appear.
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Retina begins to form as well.
References:
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The baby’s limbs begin to become more distinct.
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Fingers begin to form.
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Ears and eyes become more apparent.
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The nose and upper lip have formed.
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The “C-curve” becomes less clear as the neck and torso begin to straighten slightly.
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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)
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The baby’s arms are more distinct as the elbows develop.
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The toes on the legs are also more clear-cut.
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The appearance of eyelids.
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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.
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The fingers and toes become more clear-cut defined as the webbing goes away.
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Eyes and ears continue to develop.
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The baby has brain waves and the heart is beating at about 180 beats per minute.
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The baby has internal sex organs.
References:
Fetal development: The 1st trimester - Mayo Clinic
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The baby is now a fetus.
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The body continues to develop (eyes, eyelids, ears, and other organs).
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Buds that develop into future teeth appear.
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The baby’s genitals begin to form, based on the sex chromosome pair (XX– girl, XY– boy).
References:
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The baby’s face has taken on a more recognizable appearance.
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The baby also begins to develop fingernails.
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Kidneys can secret urine.
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May develop more complicated reflexes such as sucking.
References:
Pregnancy Week 12 - 12 Weeks Pregnant
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Movement of baby’s intestines from the umbilical cord into the abdomen.
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Baby’s head is now â…“ of the body.
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The kidneys and urinary tract are functional.
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Continuous development of facial features and the baby’s head can now move.
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A layer of fine hair (lanugo) covering the fetus’s skin starts to grow.
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Baby weight is at more or less 25 grams (0.88 ounces).
References:
Pregnancy: 13 - 16 weeks (news-medical.net)
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Arms are at almost full length.
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The neck is better defined and eyebrows are formed.
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Some babies may begin to suck their thumb.
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The baby can swallow amniotic fluids and the kidneys have started working and producing urine.
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The ovarian follicles start forming (if a baby is female) or the prostate starts to appear (if a baby is male).
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Baby weight is 40 grams (1.41 ounces)
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References:
healthy-pregnancy-guide.pdf (canada.ca)
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The baby’s bones are hardening and the muscles are developing.
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Their short legs are now growing longer every day.
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They develop hearing abilities though their eyes are still closed.
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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.
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The heart is able to pump 24 liters of blood daily.
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Baby’s head is more upright.
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The baby is about to have a 3-week growth spurt.
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The nervous system continues to develop, and the baby starts moving its arms and legs.
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The baby may start punching around inside you.
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Development of baby’s scalp pattern.
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Baby weight is 100 grams (3.53 ounces)
References:
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Hearing keeps developing, and the baby can start to hear your voice.
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The development of unique patterns of fingerprints and toeprints.
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Fat stores begin to form under the baby’s skin.
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Skeleton continues to harden.
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Weight of 140 grams (4.94 ounces).​
References:
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Mid-pregnancy ultrasound scan can be done this week.
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In the case of a girl, the uterus is in place, and her vagina and fallopian tubes are continuously growing.
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In the case of a boy, his penis will be distinct.
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The main branching tubes in the lungs start to form tinier tubes.
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Can respond to sound.
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Myelin (a protective layer of covering) starts to form around the nerves.
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The baby is 190 grams (6.7 ounces)
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References:
18 weeks pregnant: fetal development - BabyCenter Canada
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The brain forms specific areas for all 5 senses (smell, taste, hearing, vision, and touch).
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Hairs start to grow out of the scalp.
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A white protective coating called vernix caseosa appears on the baby’s skin.
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Teeth begin to grow.
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Main airways in the lungs (bronchioles) start to form.
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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.
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The first flutters you feel are called ‘quickening’ if this is your first pregnancy.
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Plenty of growing room, and the baby is able to stretch and flex.
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Baby’s regular activities include thumb-sucking and winking of his/her eyes.
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Baby weighs 300 grams (10.58 ounces).
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The first poop can be seen in the intestines.
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References:
BBC-7th-edition-FINAL-Nov2019.pdf (gov.bc.ca)
Week 20 of Pregnancy: What's Going On Inside | HealthLink BC
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Able to make facial expressions.
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Their transparent skin gradually turns from pink to red.
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The liver and the spleen have been working hard to produce more blood cells
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Baby’s movements are more coordinated.
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Baby can swallow small amounts of amniotic fluid.
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360 grams (12.7 ounces) of weight
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References:
21 weeks pregnant: fetal development - BabyCenter Canada
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Head and body hair called lanugo thickly covers the baby.
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Eyes have developed and irises are not fully pigmented.
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The baby is able to clear excess water in its body by peeing.
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Lower limbs are fully developed.
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Mammary glands which are responsible for making breast milk continue to grow for a baby girl.
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For a baby boy, testes start to descend from his pelvis into the scrotum, and they usually reach the scrotum in the third trimester.
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The baby is 430 grams (15.17 ounces) of weight
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References:
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Baby starts to have rapid eye movements.
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Fingerprints and footprints begin to form.
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Baby is more sensitive to sounds, and may respond to certain sounds.
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Baby’s heart beats a little stronger.
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Skin starts to appear red.
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Weighing more than 500 grams (1.1 pounds).​
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References:
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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).
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Sleeping and waking up patterns are more defined.
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The bigger they become, the stronger punch you may feel.
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The rapid growth of the brain.
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Skin is wrinkled and red.
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Weighs 600 grams (1.32 pounds)
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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.
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Wrinkled skin starts looking smooth as that of a newborn.
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Scalp hair growth continues.
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Baby’s startle reflexes are developing
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Eyelids are separating.
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Nostrils and nose start to work by ‘breathing’ amniotic fluid.
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Rapid eye movement (REM) occurs throughout most of the baby’s sleep time even though the eyelids are closed.
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Baby vigorously responds to touch and sound.
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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
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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.
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Baby might distinguish the different voices of the mother and her partner.
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Baby’s eyelids open for the first time.
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Full development of taste buds.
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760 grams (1.68 pounds) of weight
References:
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Formation of eyelashes.
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The nervous system continues to mature.
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Baby keeps changing their position in the uterus.
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The baby is putting on weight and fat continuously.
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Baby might have hiccups.
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Weight of about 875 grams (1.93 pounds)
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References:
Embryonic & Fetal Development (scdhec.gov)
Fetal development: The 2nd trimester - Mayo Clinic
27 Weeks Pregnant | Pregnancy | Start for Life
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This week is the beginning of the third trimester.
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The baby’s central nervous system (CNS) can now orchestrate paced breathing and control body temperature.
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Baby moves around to respond to bright lights.
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The baby’s heart rate is 140 beats per minute (bpm).
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The senses of hearing, smell, taste, and touch are developed and functional.
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Weighs around 1kg (2.2 pounds). ​
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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.
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The baby can tell the difference between bright sunlight and artificial light through the uterine wall.
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Baby’s first smile may appear, especially during sleep.
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The baby had more hiccups.
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Skin becomes smoother as more fat begins to build up.
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The baby weighs 1.13kg-1.36kg (2.5 to 3 pounds)
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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.
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Formation of red blood cells in the bone marrow.
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Thicker hair on the head.
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You may experience ‘false’ labor contractions called Braxton Hicks.
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Baby is most likely in the head-down position and will descend further into your pelvis in the following weeks.
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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)
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Most organ development is complete.
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Rapid weight gain.
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Skin continues to thicken.
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The brain is more sophisticated, and brain connections between nerve cells are growing rapidly.
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The brain can process information and can detect signals from the five senses.
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Can determine familiar sounds and voices.
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The baby weighs about 1.5kg (3.31 pounds)
References:
Your Pregnancy Week by Week: Weeks 31-34 (webmd.com)
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Visible toenails.
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The fine hairs covering the baby’s skin (lanugo) start to shed.
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Most babies are positioned head-down (also called cephalic presentation) in the 32nd and 36th week.
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Baby continues to gain weight, and may take up most space in the uterus
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Weighs around 1.7 kg (3.75 pounds)
References:
Your Pregnancy Week by Week: Weeks 31-34 (webmd.com)
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The pupils can change size to detect changes in light.
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The brain and nervous system are completely developed.
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Hardening of bones, except the skull.
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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.
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Fingernails grow long enough to reach the tips.
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Skin is pink.
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The fat build-up continues.
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The baby weighs about 2.1kg (4.6 pounds)
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References:
Embryonic & Fetal Development (scdhec.gov)
34 Weeks Pregnant | Pregnancy | Start for Life (www.nhs.uk)
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Continued accumulation of fat under skin, and the baby looks chubby. This keeps baby warm after birth.
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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.
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It’s harder for the baby to move, but the Mom should still be able to feel some movement.
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Baby’s skull bones are not joined together to comparatively easily go through the birth canal.
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Lungs are properly developed by now, and the baby can breathe after birth.
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Weighs about 2.63kg (5.8 pounds)
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References:
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Baby has a firm grasp.
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The head might begin turning towards the pelvis.
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Babe is getting ready to come out
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Weighs about 2.9kg (6.3 pounds).
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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)
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The baby is not having any significant development, and the baby has taken on his/her final birth appearance.
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The baby begins to store meconium in the bowels (Meconium are contents from the womb; excreted out after birth).
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The baby weighs about 3.08 kg (6.8 pounds)
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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!
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The baby’s skin has changed from pink to white.
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The firmly formed layer of skin aids with survival after birth (to protect internal organs and control body temperature).
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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
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The baby is fully developed and ready to come out.
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There is barely any space for the baby to move.
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Weighs about 3.5 kg (7.63 pounds)
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References: