If you have regular periods, the end of week four will give you an inclination of whether there is a possibility that you are pregnant, when you find that your period doesn't do its normal rounds. Once four weeks are up you can carry out a pregnancy test. Hold off as long as you can.
You may experience some of the symptoms of menstruation like having cramps, and think that you are going to get your period. But these symptoms can also be early pregnancy symptoms. You may also start to feel nausea.
Anyway the embryo at four weeks is extremely tiny, about 0.014 to 0 .04 inches long. That's incredibly small. It has travelled about seven days to the uterus, and is now embedding itself into the uterus's endometrial lining. When it embeds itself it may cause some spotting. If your period doesn't flow as it normally does than its highly likely that you are pregnant. To confirm go for a pregnancy test.
Home pregnancy tests may not be very reliable. If you are in a hurry just go to the clinic and get a blood test done. It will show the presence of the hormone, human Chorionic Gonadotropin (hCG). The minute you find that you test positive for pregnancy, then you must make your first pre-natal appointment with your doctor, which will probably be after a few more weeks.
It's a happy time for all in the family if you are really pregnant. If you are, then congratulations, you must start to take care of yourself more than before, because now you have an extra one with you.
You must eat well but that does not mean eat twice as much in quantity, it means eat twice as much in quality. To eat and not put on extra weight, you must eat good nutritious food that is full of raw vegetables and fruits, as they will supply a lot of vitamins for the baby to use in its development. You must also not expose yourself to any pollution or substances considered dangerous to the embryo. These pollutants can affect the development of your baby. Also discuss with your doctor, if it's better or not for you to stay off certain medication, for the good of the baby.
Your baby in the fourth week, is in an embryonic stage, and the group of cells is called a blastocyst. Even though it's extremely tiny, it's extremely busy embedding ever deeper into the endometrial tissue of the uterus, becoming partly embryonic where the embryo develops and partly trophoblastic where the placenta develops. Until the placenta develops enough, the embryo uses food from the yolk of the egg. It also is creating the beginnings of the amniotic cavity, where later the fetus will float in a fluid called the amniotic fluid.
The embryo at this point has three different layers of tissue. The outermost layer is called the ectoderm, which will develop into skin, hair, the nervous system and eyes. The mesoderm or middle layer will develop into muscle, bones, kidneys, sex organs and the heart. And, the inner most layer or endoderm will became the lungs, liver and intestines.