Baby developing inside you
over the weeks and months
Week Four: Implantation
|4 weeks - The fertilized egg immediately begins dividing and floats down into the uterus. Immediately upon fertilization your little one is set as a boy or a girl. Ladies, this is one that you can not take credit for since it is up to the sperm to determine the sex of your baby. Sperm carries either a "X" (girl) chromosome or a "Y" (boy) chromosome. |
The sex of your baby is predetermined by the fathers sperm chromosomes.
The cells contains all of the genetic information (DNA) necessary to become a child. The baby begins to form from this single fertilized egg, the cell starts to divide itself into 2 cells, then 4, 8 and so on rapidly. Forty-six chromosomes combined, which pre-determine all of a person's physical characteristics. The fertilized egg is still rapidly dividing as it floats down from the fallopian tube and towards the uterus. The embryo first moves into the uterus at about 80 hours after ovulation. The implantation process begins about 3 days later. When it reaches the uterus, the fertilized egg burrows into the lining of the uterus.
At this stage the fertilized egg is now called a blastocyst, it is a fluid filled cluster of 50 to 60 cells, still multiplying madly. Implantation of the blastocyst occurs at about day 5 to day 8 of embryo development. IVF embryos are usually transferred into the uterus around this stage. The developing embryo is only one-hundredth of an inch long, but is rapidly developing. It can reproduce itself through twinning at any time up to about 14 days after conception; this is how identical twins are caused.The site of the implantation will be the place where the placenta attaches to the uterine wall. After the blastocyst has implanted, it will start to release a hormone called human gonadotrophin hormone (hCG) into your blood stream. (hCG levels provide the basis for detecting a pregnancy with a pregnancy test.)
The hCG level starts off very low, but the concentration rapidly increases on the following days to produce physical pregnancy signs in the woman. These hormonal signals tell the lining of the uterus to stay in place and not disintegrate as it normally would during menstruation.
At this time you may have an intuitive sense that something is up, you might have a strange taste in your mouth, or your breasts may feel a little odd. These faint clues could be the first signs that a baby is burrowing in. Your baby is the size of a pinhead !
Week by week First trimester: ultrasound scan pictures: Week 4
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