Development pregnancy week 4.

Growth of baby at 4 week of pregnancy.
Fetal development at week 4 is still in the very early stages, but many great changes are taking place! The implanted blastocyst is embedded more deeply into the lining of your uterus, and the amniotic cavity, which will be filled with amniotic fluid, is starting to form. The placenta, which plays an important role in hormone production and transport of oxygen and nutrients, is forming. Vascular networks that contain maternal blood are establishing.

Germ Layers
Different layers of cells are developing. These germ layers develop into specialized parts of your baby's body, such as various organs. There are three germ layers the ectoderm, endoderm and mesoderm.

The ectoderm will become the nervous system (including the brain), the skin and the hair. The endoderm develops into the lining of the gastrointestinal tract, the liver, pancreas and thyroid. From the mesoderm comes the skeleton, connective tissues, blood system, urogenital system and most of the muscles.

Changes in You
You are probably expecting a period around the end of this week. When it doesn't occur, pregnancy may be one of the first things you think of!

The Corpus Luteum
When you ovulate, the egg leaves the ovary. The area on the ovary where the egg comes from is called the corpus luteum. If you become pregnant, it is called the corpus luteum of pregnancy. The corpus luteum forms immediately after ovulation at the site of the ruptured follicle where the egg is released. It looks like a small sac of fluid on the ovary. It undergoes rapid blood vessel development in preparation for producing hormones, such as progesterone, to support a pregnancy before the placenta takes over.

The importance of the corpus luteum is the subject of much debate. It is believed to be essential in the early weeks of pregnancy because it produces progesterone. The placenta takes over this function between 8 and 12 weeks of pregnancy. The corpus luteum lasts until about the 6th month of pregnancy, when it shrinks, although normal corpus lutea have been found with full-term pregnancies. Successful pregnancies have also occurred when the corpus luteum was removed because of a ruptured cyst as early as the 20th day after a menstrual period or about the time of implantation.