You still cannot do a pregnancy test as yet, but if you have conceived, the fertilized egg or zygote, which has double the chromosomes present in the sperm or egg, has divided into a group of cells, called the blastocyst. The blastocyst is hollow and contains fluid. This fluid function, later called the amniotic fluid is to cushion the fetus as it's developing, and prevent it from experiencing too many shocks from the external environment. The whole blastocyst at the beginning of week three is as big as a pin head! It is so amazing that this little pin head structure is going to become a human being in about 37 weeks. How wonderful and marvelous are the processes of life. Now, let's get back to the blastocyst.
The blastocyst has just come from the fallopian tube and is ready to implant into the uterus lining called the endometrium, the endometrium usually gets sloughed off during the menstrual cycle which flows out as menses. But when a blastocyte implants itself into the endometrium, hormones are released to protect the endometrium, so that it does not slough off. However sometimes you might see some spotting. It's called implanting spotting. This happens about six days after conception which means if you do see it, it'll be towards the end of week three. Once the hormone protecting the endometrium is released, you should not see any spotting.
Once the blastocyst implants itself, it receives nutrients from the wall of the uterus at the point of implantation. The blastocyst or embryo actually consists of two parts. One goes on to produce the embryo and is called the embryoblast, while the other is called the trophoblast. The trophoblast will develop into the placenta, which will supply nourishment to the fetus, and later to the unborn baby. By day 17, the placenta would have connected the baby with the mother, and nourishment is sent to the baby.
This is the time when folic acid is important for the healthy development of the neural tube so that no defects develop. You can take a diet rich in folic acid, like green leafy vegetables, asparagus and broccoli; whole wheat and potatoes; lentils, peas and soya; fruits like peaches, oranges and bananas. Or, you can take some pre-natal folic acid.
You must also be well-nourished so that the baby grows well in the beginning stages and you create a healthy baby. Eat foods rich in protein, such as legumes, beans, peas and brown rice. Calcium is very important for the development of strong bones, and so takes lots of milk and dairy products. Iron is important for the production of blood, and it is found in legumes, and other types of beans; other vegetables like broccoli, brussel sprouts, asparagus; dried fruits like raisins, prunes, dates and apricots; nuts; and molasses.
By now you would have given up smoking, alcohol, coffee and tea. When you go into pregnancy it's good to start meditating as it'll calm your mind and relax yourself. Make a point to be happy and positive most of the time, as these are the feelings you are going to pass to the baby.