Chronological development of a baby

by Matt Slick

1. 1st week (1st month)1
   1. Sex of baby is determined.
   2. Genetic traits are determined.
   3. Embryo travels from fallopian tube to the uterus.
2. 2nd week (1st month)
   1. Egg is implanted on the wall of the uterus.
   2. Placenta develops.
3. 3rd week (1st month)
   1. Heart begins to develop, 18-25 days.
   2. Brain begins to develop.
   3. Intestinal tract begins to develop.
4. 4th - 5th weeks (1st month)
   1. Vertebra begins to develop.
   2. Blood flow begins.
   3. Eye development begins.
   4. Arm and leg development begins.
   5. The umbilical cord begins to form.
5. 6th week (1 - 2 months)
   1. Fingers and the toes appear.
   2. Nose and ears develop.
   3. Joints are developing.
6. 7th week (1 - 2 months)
   1. All essential organs are developing.
   2. Eyelids form.
7. 8th week (2 months)
   1. Muscle contraction occurs.
   2. Facial features become more prominent.
   3. Heart has four chambers.
8. 9th - 12th week (2 - 3 months)
   1. The baby is about 3 inches long.
   2. The neck develops.
   3. Arms and legs begin to lengthen.
   4. Genitals are well defined.
9. 13th - 16th weeks (3 - 4 months)
   1. The baby is about 6 inches.
   2. Hair begins to develop.
   3. The baby moves.
   4. Lungs develop.
   5. If female, the ovaries contain about 2 million eggs.
   6. The face is more developed.
   7. The baby can suck its thumb.
10. 17th - 20th weeks (4 - 5 months)
    1. The baby is about 8 inches.
    2. Eyebrows form.
    3. Nails on fingers and toes form.
    4. Movement can be felt by mother.
    5. The circulatory system is working.
    6. Swallowing begins to occur.
11. 21st - 24th weeks (5 - 6 months)
    1. The baby is about 11 inches long.
    2. The baby weighs about 1.5 pounds.
    3. Fingerprints form.
    4. The baby can hear and react to sounds from outside the womb.
12. 25th - 28th weeks (6 - 7 months)
    1. The baby is about 15 inches long.
    2. The baby weighs about 2.5 pounds.
    3. Survivability outside the womb is possible.
    4. The baby can react to light from outside the womb.
13. 29th - 32nd weeks (7 - 8 months)
    1. The baby is about 16 inches long.
    2. The baby weighs about 4.5 pounds.
    3. All bones are fully developed.
14. 33rd - 40th weeks (8 - 9 months)
    1. The baby is about 18 - 21 inches long.
    2. The baby weighs about 6 - 8 pounds.
    3. The baby is ready to be born.
    4. Sleep patterns are apparent.
    5. Strong movement is very apparent.

This section is also available in: Español

• 1. www.allhealth.com