You will feel the early symptoms of pregnancy by the aid of hormones produced. The fullness and sensibility in breasts are the most common complaints at that week. Continuing sleepiness and fatigue are also among the common symptoms observed. You may need to go to toilet frequently since the growth in your uterus reduces the capacity of your bladder. Even if you have not visited your doctor yet, see your doctor immediately since it is the time to meet with the living organism in your body. Your doctor will display the gestational sac in the vaginal uterus by ultrasonography. If the gestational sac cannot be viewed on the ultrasonography, it can be ectopic pregnancy. It is a serious case that might risk your life, so it will be your best interest to see your doctor as soon as possible for the first control.
After fertilization, at the 16th day, evolution speeds up. From the endoderm layer to the membranes covering the lungs, tongue, amygdale, urethra, bladder, and digestion system develops; muscles from the mesoderm, bones, lymph system, spleen, blood cells, hearth, and lungs, reproduction and excretion systems differentiate. Skin, nails, hair, lens layer of the eyes, hearing system, nose, sinuses, mouth, anus, enamels, pituitary gland, breast tissues, neural system, and ectoderm layer also differentiate. After 17-19 days, embryonic area seems like a pear. Head part is larger than tail part. Ectoderm layer thickens to form neural plate. The sides of the plate curves and called as neural sulcus. This is the template of the neural system of the embryo and also one of the first developing organ systems.
At the end of this week, the blood cells of the baby form, and canals among epithalamiums cells also form. When we reach 21st day, somites stem from mesoderm begin to appear at two sides of neural sulcus and from cauda. Endocardiac cells form the primitive heart tubes in the early embryo.