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Week 1
Week 1 is the week of the last Menstrual period and is the start of pregnancy. -
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Week 2
Fertilization occurs this week, and it is when the egg is fertilized by a sperm. When it is fertilized, the egg accepts no more sperm. -
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Week 3
With all 46 chromosomes together, the cells grow rapidly within the fertilized egg. Implantation begins 3 days after entering the uterus from the fallopian tube. -
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Week 4
The fertilized egg implants into uterine wall. It releases hCG and is about 1/100 of an inch in size. -
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Week 5
In this week, the placenta develops. The brain and spine start to develop at this stage and the embryo grows to 4-5mm. -
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Week 6
The blood cells, blood vessels, and heart begin to form, as well as the ears and eyes. The buds for arms and legs are in place. -
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Week 7
The embryo is 13mm. The heart is beating and the mouth, lungs, digestive tract begin to form. -
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Week 8
The embryo practices moving and grows to about 18mm in size. The face takes shape during this period. -
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Week 9
The embryo is now 30mm in size. The heart is complete and brain waves can be measured. -
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Week 10
The embryo is now called a fetus and is about the size of a small strawberry. The muscles develop at this point. -
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Week 11
Cartilage starts calcifying to bone. The genitals begin to form. Now 1.5 inches in size. -
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Week 12
Fetus is about 2.5 inches and moves spontaneously. It can suck its thumb and get hiccups. -
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Week 13
The fetus is about 2.91 inches and gender bay be able to be identified. The ribs also start to appear. -
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Week 14
The fetus is about 3.5 inches. The kidneys produce urine and hair appears. -
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Week 15
The fetus is over 4 inches. Fingernails and toenails become present and the fetus can make a fist. -
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Week 16
Fat forms underneath the skin. The fetus can hear external voices and also learns how to breathe. -
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Week 17
The fetus is about 9 inches head to toe and swallows up to a liter a day of amniotic fluid. The retina becomes sensitive to light. -
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Week 18
The vernix forms on the skin. The fetus goes through motions of crying but with no sound. -
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Week 19
Reproductive organs become distinct and features of the heart are now visible. -
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Week 20
The fetus can react to outside sounds, and its heart can be heard with a stethoscope. -
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Week 21
The bone marrow starts making red blood cells. The fetus is about 10.5 inches long. -
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Week 22
Taste buds start to form on tongue and the fetus develops a regular sleep rhythm. It is also around 11 inches long. -
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Week 23
At this point the fetus develops a sense of balance and the eyebrows become visible. -
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Week 24
The fetus is now 12 inches long. Muscle coordination has been improved and lungs start to develop branches of respiratory tree. -
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Week 25
The fetus is 13.5 inches long. Its brain is growing rapidly and the hands and reproductive organs are fully developed. -
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Week 26
The fetus is now 14 inches long. Its eyes begin to open and the hands are active enough for the fetus to suck its thumb. -
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Week 27
It is now 14.5 inches long. Its eyes can blink, open and close and it also recognizes certain voices. -
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Week 28
The fetus is now 14.8 inches. Its eyes move (REM) and it dreams. Also the milk teeth developed under the gums. -
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Week 29
It is now 15 inches and has the ability to taste and respond to pain. -
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Week 30
At 16 inches, the fetus's wrinkled skin becomes smooth and it is now able to control its own body temperature. -
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Week 31
The fetus is 16.5 inches and the eyes are now completely open. Any nearby loud noises may startle the fetus. -
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Week 32
The fetus is now 17 inches and the toenails and fingernails are completely formed. -
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Week 33
It grows to 17.5 inches. The lanugo starts to disappear. -
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Week 34
Now at 18 inches fat plumps up around the arms and legs of the fetus. -
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Week 35
The fetus grows to 18.5 inches and its reflexes are coordinated and its lungs are almost fully developed. -
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Week 36
With the fetus now being 19 inches, the only organ yet to mature is lungs. -
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Week 37
Because of its size of 19.5 inches in its crammed environment, the fetus's body part may protrude from the mother's stomach. -
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Week 38
Now that the fetus is 20 inches, the development is complete, and its only focus is gaining weight. -
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Week 39
Remaining at 20 inches, the fetus enters its final birth position. The lanugo is mostly gone at this point. -
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Week 40
The fetus maintains the size of about 20 inches, and everything is developed and ready for birth.