Week 4

My Baby's Development

Four weeks into your pregnancy, your baby (called an embryo) consists of two layers of cells (the epiblast and the hypoblast) that eventually develop into all of your baby's organs and body parts. Two other structures that develop at this time are the amnion and the yolk sac. The amnion, filled with amniotic fluid, surrounds and protects the growing embryo. The yolk sac produces blood and helps to nourish the embryo until the placenta takes over that role.

My Body

Your baby continues to implant in your uterus, burying itself deep within the endometrium. Once implanted, your baby starts to produce a hormone called human chorionic gonadotropin (hCG), which helps to maintain the lining of the uterus. The hormone also sends a signal to the ovary to stop releasing an egg each month, which stops your monthly periods. Some women experience slight cramping and spotting of blood during the week 4 while implantation is taking place. They may mistake this as a period as it also occurs around the time their monthly period was due.

hCG is the hormone that is measured in pregnancy tests. A pregnancy test will probably be able to detect your pregnancy by this week. hCG also causes the symptoms of pregnancy such as fatigue, tingling or aching breasts and nausea. These might lead you to believe your period will be starting any day because the first pregnancy symptoms resemble premenstrual syndrome (PMS). But by the end of this week, your expected menstrual period will not take place. Because you are pregnant!