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Home   1st Trimester   5 Weeks Pregnant

You’re 5 Weeks Pregnant!

What’s Happening During Week 5:

Congratulations you have missed your period and the pregnancy test is positive.

What makes a pregnancy test positive? Pregnancy is a time of great hormonal activiity. Your existing hormones raise dramatically and new ones are produced to support the pregnancy in the early days. The pregnancy hormone, called human chorionic gonadatropin or (HCG) is produced by trophoblastic tissue. Trophoblastic tissue is the future placenta and the outer layer of the blastocyst and it is this hormone that is detected in your urine and your blood that gives the pregnancy test it’s positive results.
Fertiliztion most often occurs within a day of ovulation (day 15 of a 28 day cycle) typically in the longest and widest portion of the fallopian tube as I described in week 3. After the fusion of the sperm and the egg this new form is called a zygote. A zygote is the earliest developmental stage of a human and is a cell containig 46 chromosomes, formed by the joining of 23 chromosomes from each parent.
This new cell remains a zygote for about 2 days during which this cell mass divides repeatedly as it travels down the fallopian tube towards the uterus. Once it forms into a solid ball of 12 or more of these cells, the zygote begins to resemble a mulberry hence this new structure is now referred to as a morula which is Latin for mulberry. ( morula video ) This morula enters the uterine cavity on day 18 or 19 of the cycle. Fluid within the endometrial cavity penetrates this cell mass to create a central cavity. When this happens the morula is transformed into what is now known as a blastocyst. When this happens the blastocyst and its tissue is divided into two very important layers. The outer layer, the trophoblast creates the chorionic membranes and the fetal contribution to the placenta. The inner cell layer develops into the embryo, amnion, umbilical cord and the yolk sac. By the end of the 3rd week the blastocyst begins to implant into the thickened endometrium. During the 4th week the blastocyst measuring only the size of a pin head in diameter becomes fully imbedded into the emdometrial tissue. The endometrial tissue is the lining of your uterus or womb that has become thick in preparation for this implantation. It is at this time when the blastocyst and trophoblastic tissue invades the endometrium that a small amount of bleeding can occur, called implantation bleed, and flows out of the vagina and can sometimes be confused with a menstrual cycle.
This is a time when the cells multiply and differentiate rapidly. Part of this formation is the yolk sac a structure that provides nutrients in the early days and a tiny embryo develops between the yolk sac and the amnion and primitive placental circulation now has been established. At this time this formation of conception has grown to about 2 to 3 mm and can be identified by state of the art ultrasound equipment as a tiny fluid filled sac. 
During week 5, the final week of the conception stage of pregnancy you have missed your period and pregnancy can now be confirmed with the level of HCG in your blood or urine. The fluid filled sac known as the chorionic or gestational sac has grown to about 5mm and the yolk sac can be identifed within this fluid filled sac. The embryo has transformed itself into three different layers the ectoderm, mesoderm and endoderm despite these transformations only the fluid filled sac can be detectable by ultrasound and not the embryo just yet.
The ectoderm, the top layer will form baby’s brain, spinal cord, nerves and backbone. This layer will also give rise to baby’s skin, hair, nails, and even tooth enamel.
The middle layer, or mesoderm forms your baby’s muscles, cartilage, bone, and subcutaneous (under skin) tissue. The mesoderm also forms
into baby’s heart and circulatory system, in fact, the tiny heart begins to divide into chambers and beat and pump blood and soon all cells will dance to the same beat as the heart. 
The endoderm the third layer, will form into the thyroid, liver, and pancreas, the gastrointestinal tract, as well as part of the urinary system.
As a very new Mom you may already be experiencing fatigue, tender breasts and frequent urination. Now is the time to slow down and take extra care of yourself as this is a vulnerable time for the growing embryo.



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