2. EMBRYONIC DEVELOPMENT: 4-8 weeks of embryo development.
| 1.5 WEEKS: |
Completely developed embryo.
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| 2nd WEEK: |
Primitive streak.
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| 3rd WEEK: |
Central nervous system begins to develop.
Heart development initiated - beating begins. |
| 4th WEEK: |
Complete mass (baby and chorion, etc.) - about 1" long and the size of a pigeon's egg.
Embryo inside is about 3/8" and weighs less than 1 gram.
Outpouching from anterior brain - early eyes - limb buds of arms and legs. |
| 5th WEEK: |
Nose and lips formation begins.
Brain is developed into 5 components and lumen of spinal cord is continuous with brain vesicles allowing free cerebral spinal fluid flow. |
| 8th WEEK: |
Major organs begin development.
Now about size of hen's egg.
Embryo is 1" long and about 4 grams.
Hands and feet are seen.
Baby is extremely reactive to its environment.
Male sex hormone (testosterone) produced by testes
Masculine development in males - no change in females. |
| 12th WEEK: |
Embryo is about the size of a goose egg.
Placenta is well established and weighs more than the baby.
Baby is approximately 3 1/2" long and weights about 60 grams (2 oz.). Fingers and toes can be seen.
This is the end of the embryonic stage. |
3. FETAL DEVELOPMENT
| 14-16th WEEKS: |
Brain developed to the point that baby can suck, swallow and make irregular breathing movements. |
| 16th WEEK: |
6", 6 oz. (180 grams)
Complete closure of nasal septum and palate.
Fetal heart beat heard with amplification.
Fetal movement is recognized.
Sex is distinguishable now.
Meconium formation in intestines. |
| 20th WEEK: |
8", 10 oz. (300 grams).
Lanugo - fine hair covering over entire body, probably for protection of skin.
Vernix Caseosa - secreted by fetus, made of sebaceous material, and other materials and is probably protective.
Has some antimicrobial substances.
Fetal heart beat heard: 120-160 beats per minute. |
| 24th WEEK: |
12", 1 1/2 lbs. (720 grams).
Baby is maturing, not considered viable (until 28 week). |
| 28th WEEK: |
Baby can survive outside uterus if lungs capable of breathing.
10-20% survival if born at this time.
14", 2 1/2 lbs.
Viable (legally).
Fetus in breech position until 32nd week. |
| 32nd WEEK: |
Maturing. 50% survival if born at this time.
Should turn to head down position.
16", 3 1/2 lbs. (1680 grams).
Skin is red and wrinkly.
The downy type hair is less plentiful and has more vernix. |
| 30-34th WEEK: |
Baby is the same size as placenta. |
| 36th WEEK: |
94% survival rate if born at this age.
18", 5 1/2 lbs.
Has some subcutaneous fat.
The baby stores things during this last trimester.
Mother should watch her weight at this time.
Fingernails are now at the tips of the fingers. |
| 40th WEEK: |
Full term. 20", 7 lbs. (3360 grams).
Length is better indication of maturity of fetus.
Very little lanugo, lots of vernix. |
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