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Fetal DevelopmentBaby developing inside you over the weeks and months |
Weeks, Months and Trimesters Guides | ||||||||||
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Week Two: Fertilization | ||
2 weeks - Every month, about three to 10 eggs receive a hormonal signal that cues them to mature and prepare for ovulation. At the same time, the uterus is forming a blood rich lining that is called the endometrium. This will thicken, upon fertilization, to form a sack strong enough to carry and cushion your baby throughout the entire pregnancy. In one of the ovaries, the eggs ripen in fluid filled sacs called follicles. Eggs, also known as ova, are the largest cell in the human body, about 1/175th of an inch or 1/7th of a millimeter. Around the 14th day, one of the eggs is released and travels down into the fallopian tube. This is ovulation. The egg then starts to travel down the fallopian tube, coaxed by tiny finger like projections called fibrae.![]() If in the next 36 to 48 hours, just one of the 350 million sperm in the average ejaculate can get all the way from the vagina through the uterus and into the fallopian tube to penetrate the egg, the egg will become fertilized. The sperm and egg join in the fallopian tube and fertilization has occurred. Only one sperm will break through, and the egg instantly shuts down. No more sperm will be admitted. Identical twins or multiples may be formed if the egg then splits in two. Fraternal twins or multiples will be formed if more than one egg gets fertilized. ![]() The baby begins to form from a single fertilized egg to a cell that has divided itself and is now multiplying rapidly. Every sperm carries a half-set of genetic information with it, including an X or Y chromosome which will determine your baby's gender. The egg carries the other half set and the X chromosome. These chromosomes combine, which pre-determines all of a person's physical characteristics. Thirty hours later the developing embryo is still rapidly dividing, as it floats down from the fallopian tube and towards the uterus. | ||
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