Friday, November 30, 2012

First Trimester : Week 3

Posted by umi_chan at 5:18:00 PM

3 weeks pregnant

Fertilisation
The process of fusion between your egg and a single sperm takes around 24 hours. Only one sperm makes it through to the centre of the egg, although a lot battle it out to be the one and only. At the moment when one sperm is successful, the egg builds up a protective wall around itself to stop others from entering. Eventually, the other sperm give up trying. If one egg is fertilised by a single sperm and divides separately, identical twins are formed at this very early stage.

The newly fertilised egg is now officially called a zygote and it starts dividing into more and more cells, until around the 3rd day, when what was originally 2 cells, have now become 12. The zygote is still in the fallopian tube at this stage, though it is steadily finding its way down to the uterus where it will stay, hopefully for another 37 weeks or so. Little finger like projections of hair called cilia, line the fallopian tube and wave the zygote along to discourage it from settling in where it shouldn’t. It takes around 60 hours for the fertilised egg to weave its way down to the uterus, by which stage there are 60 cells, all with a predetermined job and a specialised function. The outer cells will form the placenta; the inner cells will form the baby.

 Around a week after the egg has been fertilised in the fallopian tube, it embeds in the lining of the uterus. By now, there are 100 cells bunched together and it is called a blastocyst. At this early point, the pregnancy hormone Human Chorionic Gonadotrophin is produced and it is this hormone which can be detected in your urine or blood when a pregnancy test is done. If the signals to keep producing HCG aren’t received, the lining of the uterus isn’t needed and is shed in your next period.

Your baby’s changes this week
Pregnancy Week by Week – 3 Weeks Pregnant
So far your baby is barely the size of a pin head. It is still a cluster of cells and doesn’t look anything like what it will become. But, it is rapidly dividing and multiplying over the full 24 hours of each day.

 

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