The first day of the pregnancy is the first day of the last menstrual period preceding it: the approximately 40-week countdown starts then.
On the 14th day of the menstrual cycle, the mature ovum is released from the ovary into the oviduct, where it becomes fertilized. Thus, in reality a pregnancy is only 38 weeks long. A new life is established on the result of a race between 30-40 million sperms that all try to fertilize the ovum, and usually only one sperm wins (except in the case of twin pregnancy). The now fertilized egg continues its journey towards the uterus, and reaches it in approximately 3-5 days. Implantation takes place on the 9-10th day after fertilization, when you are already 4 weeks pregnant. Conception does not have any detectable signs at this early stage. Whether your baby will be a boy or a girl is set right at the moment of fertilization, as it is based on the so-called sex chromosome. At the moment of conception, the egg carrying an X chromosome fuses with a single sperm. If the sperm carries an X chromosome, the sex chromosome of your child will be an XX, meaning a girl, and if the sperm brings a Y chromosome, the result will be an XY chromosome pair, a boy.
THE EXPECTANT MOTHER
By the time you notice the first signs of pregnancy, you are most likely to have been pregnant for 2-3 weeks. The reason for this is that hormonal changes, nausea and headaches are the results of implantation, which takes place around week 3. At the same time, you might experience cramps and spotting as well, but they are not very common. The slight bleeding is caused by EPF (Early Pregnancy Factor) hormones that your body produces in order to suppress the immune system, so that your body does not detect the embryo as an intruder. Due to the changes of your hormonal levels, you become more sensitive to smells and flavors, and you might feel more irritable than usual.
The fertilized egg is called a zygote. It starts multiplying 12-20 hours after conception, while it is on its way to the uterus. This continues until it becomes as big, round and solid as a pinhead, and from then on, it is called a morula. The morula continues to multiply, and by the time it reaches the uterus, it consist of roughly 64 cells, which develops into a set of fluid-filled cells, a blastocyst. The surface of the blastocyst consists of a layer of large and flat cells. Later this layer of cells develops into the placenta and partly the embryo sac, whereas the cells at the core of the cluster become the embryo. The placenta connects to the uterine wall to ensure nutrient uptake and waste elimination.
The embryo sac is formed from the wall of the blastocyst, and the inner layer of the wall becomes an amniotic sac that encompasses the embryo. The clear liquid contained inside is called the embryo water.
The embryo itself starts to develop from week three onwards. Concerning the development of the baby, the embryonic period is the most important as his organs are formed during this time.
Pregnancy causes many inward and outward changes in your body, so consequently a change in your lifestyle is inescapable. Avoid drinking alcohol and both active and passive smoking. Pay attention to nutrition: make sure your diet contains enough protein, vitamins and trace elements. Throughout your pregnancy, be more hygienic than usual. While you are expecting, you can have sex with your partner the same as before, but be prepared that your libido might be uneven.