Even though you may not feel that you’re pregnant yet, you have a baby growing and developing inside of you! Although your baby was just conceived, he or she is working overtime. The fertilized egg goes through a process of cell division. About 30 hours after fertilization, it divides into two cells, then four cells, then eight, and continues to divide as it moves from the fallopian tube to the uterus. By the time it gets to the uterus, this group of cells looks like a tiny ball and is called a morula.
The morula becomes hollow and fills with fluid — it is then known as a blastocyst. Near the end of this week, the blastocyst will attach itself to the endometrium, the lining of the uterus. This is called implantation. The implantation in the uterus creates an essential connection — the endometrium will provide the developing embryo with nutrients and will remove wastes. Over time, this implantation site will develop into the placenta.
Adequate intake of certain nutrients, such as folic acid, protein, calcium, and iron, is essential for nourishing your baby. A folic acid supplement — which, ideally, you’ve been taking since before you conceived — is particularly important because folic acid helps prevent defects of the neural tube (the structure that gives rise to the brain and spinal cord), which forms very early in pregnancy.
Your intake of protein, which is used to create new tissue, should increase during pregnancy. In addition, calcium is necessary for the development of bones and teeth, so make sure you’re getting a good dose of dairy products, leafy green vegetables, and legumes. Iron is essential during pregnancy as you support the continual increase of your baby’s blood volume. Good sources of iron include red meat, legumes, eggs, and leafy green vegetables.
Four weeks into your pregnancy, your baby (called an embryo) consists of two layers of cells — the epiblast and the hypoblast — that will 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, will surround and protect the growing embryo. The yolk sac will produce blood and help to nourish the embryo until the placenta takes over that role.
This week 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. It 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 this week while implantation is taking place, and they may mistake this for a period, as it often occurs around the time their monthly period was due.
hCG is the hormone that is measured in pregnancy tests. This week a pregnancy test will probably be able to detect your pregnancy! hCG also causes the symptoms of pregnancy, which can appear this week. Fatigue, tingling or aching breasts, or nausea 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 period will not take place. Your pregnancy is well on its way!