How many weeks are there in a pregnancy?
There are 40 weeks. We measure a pregnancy from the start of the women’s menstrual period. After about two weeks, the egg is released from the ovary. Fertilization can then occur. Four of the 40 weeks have already elapsed at the time she misses her first period.
When does the heart begin to beat?
At 18 days [when the mother is only four days late for her first menstrual period], and by 21 days it is pumping, through a closed circulatory system, blood whose type is different from that of the mother.
J.M. Tanner, G. R. Taylor, and the Editors of Time-Life Books,
When is the brain functioning?
Brain waves have been recorded at 40 days on the Electroencephalogram (EEG).
H. Hamlin, “Life or Death by EEG,” JAMA, Oct. 12, 1964, p. 120
Brain function, as measured on the Electroencephalogram, “appears to be reliably present in the fetus at about eight weeks gestation,” or six weeks after conception.
J. Goldenring, “Development of the Fetal Brain,”
How early do some organs form?
The eye, ear and respiratory systems begin to form four weeks after fertilization.
K. Moore, Before We Were Born, 3rd ed., 1989,p.278
Very early, e.g., glucagon, a blood sugar hormone, has been demonstrated in the fetal pancreas 6 weeks after fertilization, and insulin by 7 to 8.
F. Cunningham, “Pancreas,” William’s Obstet., 19th ed., 1993, p. 183-4
Thumbsucking has been photographed at 7 weeks after fertilization.
W. Liley, The Fetus As Personality, Fetal Therapy, 1986, p. 8-17
At nine to ten weeks, he squints, swallows, moves his tongue, and if you stroke his palm, will make a tight fist. By nine weeks he will “bend his fingers round an object in the palm of his hand.”
Valman & Pearson, What the Fetus Feels, British Med. Jour., Jan. 26, 1980
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