Development of the Embryo and Fetus
Pregnancy lasts approximately 40 weeks and is calculated from the first day of your last period, although conception will probably not have taken place until around two weeks after this. Pregnancy is divided into three trimesters. The first covers week weeks 1-13, the second trimester weeks 14-26, and the third trimester week 27 until birth.

Time
Stage of Development


Week 2



Week 4




Week 6



Week 10




Week 14




Week 18



Week 22




Week 26




Week 30



Week 40


Conception is the moment at which the sperm penetrates the ovum. Once fertilized it is called a zygote, until it reaches the uterus 3-4 days later.


The embryo may float freely in the uterus for about 48 hours before implanting. Upon implantation, complex connections between the mother and embryo develop to form the placenta.


The embryo is about 1/ 5 of an inch in length. A primitive heart is beating. Head, mouth, liver, and intestines begin to take shape.


The embryo is now about 1 inch in length. Facial features, limbs, hands feet fingers and toes become apparent. The nervous system is responsive and many of the internal organs begin to function.


The fetus is now 3 inches long and weighs almost an ounce. The muscles begin to develop and sex organs form. Eyelids, fingernails, and toenails also form. The child's spontaneous movements can be observed.


The fetus is now about 5 inches long. The child blinks, grasps, and moves her mouth. Hair grows on the head and body.


The fetus now weighs approximately 1/ 2 a pound and spans about 10 inches from head to toe. Sweat glands develop, and the external skin has turned from transparent to opaque.


The fetus can now inhale, exhale and even cry. Eyes have completely formed, and the tongue has developed taste buds. Under intensive medical care the fetus has a over a 50% chance of surviving outside the womb.


The fetus is usually capable of living outside the womb and would be considered premature at birth.


This marks the end of the normal gestational period. The child is now ready to live in outside of his mother's womb.

Side Notes

Total average weight gain for a pregnant women should be around 11.9 kg , breakdown as follows:

Baby - 3.5 kg
Placenta - 0.675 kg
Amniotic fluid - 0.8 kg
Uterine enlargement - 0.9 kg
Maternal breast tissue - 0.45 kg
Maternal blood volume - 1.5 kg
Fluids in maternal tissue - 1.4 kg
Maternal fat - 3.25 kg


Percentage constituition of weight:
Baby -- 39%
Blood -- 22%
Amniotic fluid -- 11%
Uterus -- 11%
Placenta --  9%
Breasts --  8%

Approximate baby's weight:
13 weeks - 30g
14 weeks - 60g

15 weeks - 100g
16 weeks - 135g
17 weeks - 185g
18 weeks - 235g
19 weeks - 285g
20 weeks - 340g
21 weeks - 390g
23 weeks - 440g
24 weeks - 0.5kg
25 weeks - 0.6kg
26 weeks - 0.7kg
27 weeks - 0.8kg
28 weeks - 0.9kg
29 weeks - 1kg
30 weeks - 1.1kg
31 weeks - 1.4kg
32 weeks - 1.6kg
33 weeks - 1.8kg
34 weeks - 2kg
35 weeks - 2.3kg
36 weeks - 2.5kg
37 weeks - 2.7kg
38 weeks - 2.9kg
39 weeks - 3.1kg
40 weeks - 3.4kg


Source: Fetal Development Overview [ http://www.w-cpc.org/fetal.html ]





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