Young Brunette Girl Pregnant In Her Teenage Years

The third week is the week in which fertilization occurs and the 4th week is the period when implantation takes place. In the 4th week, the fecundated egg reaches the uterus and burrows into its wall which provides it with the nutrients it needs. At this point, the zygote becomes a blastocyst and the placenta starts to form. Moreover, most of the pregnancy tests may detect a pregnancy beginning with this week.
The 5th week marks the start of the embryonic period. This is when the embryo's brain, spinal cord, heart and other organs begin to form. At this point the embryo is made up of three layers, of which the top one (called the ectoderm) will give rise to the embryo's outermost layer of skin, central and peripheral nervous systems, eyes, inner ear, and many connective tissues. The heart and the beginning of the circulatory system as well as the bones, muscles and kidneys are made up from the mesoderm (the middle layer). The inner layer of the embryo will serve as the starting point for the development of the lungs, intestine and bladder. This layer is referred to as the endoderm. An embryo at 5 weeks is normally between 1⁄16 and 1⁄8 inch (1.6 and 3.2 mm) in length.
In the 6th week, the embry will be developing basic facial features and its arms and legs start to grow. At this point, the embryo is usually no longer than 1⁄6 to 1⁄4 inch (4.2 to 6.3 mm). In the following week, the brain, face and arms and legs quickly develop. In the 8th week, the embryo starts moving and in the next 3 weeks, the embryo's toes, neck and genitals develop as well. According to the American Pregnancy Association, by the end of the first trimester, the fetus will be about 3 inches (76 mm) long and will weigh approximately 1 ounce (28 g).