What happens in the 4th week of pregnancy?

By the end of week 4 of pregnancy, you might be expecting your period (or mostly hoping not to get it). Taking a home pregnancy test at the end of 4th week may possibly confirm that you are on your way to become a mom.

You're still not "showing" and you haven't even gained weight at this point, since your baby is so small. Your hormones are undergoing a lot of changes; as such mood swings are totally normal during this time.

By the end of this week, the fertilized egg gets embedded more deeply in the lining of your uterus and the amniotic cavity, which is filled with amniotic fluid, begins to form.

The placenta has started forming and the connecting stalk- that later becomes the umbilical cord- has appeared. Until the placenta is fully functioning, the yolk sac, now present, feeds your baby. Germ layers are also developing and vascular networks containing maternal blood are being established.

Your Baby's Development

4 weeks into your pregnancy, your baby (called embryo) consists of two layers of cells —epiblast and hypoblast-that will eventually develop into baby's organs and body parts. 2 other structures that form 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 nourish the embryo until the placenta takes over that role

Your baby at 4 weeks pregnant is still extremely miniscule, about .014 to .04 inches long. Your baby will gradually start changing by 4 weeks pregnant so that he or she starts resembling a small tadpole with eyes!

Your baby will be implanting vigorously during pregnancy week 4 into the uterine lining, to ensure that he or she has a safe and secure home for the next nine months. Fetal development in general is still in the earliest stages at this point. At this point the blastocyst or ball of cells that is your baby will be imbedding deeper into the lining of the uterus. The amniotic cavity is forming in addition to the placenta being formed.

As you continue to grow, develop and expand during your pregnancy week by week, the placenta helps nourish and support your baby during the nine months of pregnancy. It consists of vascular networks and blood from your body which helps in transporting oxygen and nutrients to the fetus. There are numerous different layers of cells developing in your body, which eventually develop into your baby's organs and other body parts. Other layers develop into the nervous system including the brain.

Your Body

During the 4th week your baby continues to implant in your uterus, burying itself deep into the endometrium. Once it gets implanted, the baby starts producing a hormone called human chorionic gonadotropin (hCG). This hormone helps to maintain the lining of the uterus. It also sends a signal to the ovary to stop releasing an egg every month, which stops the monthly periods.

Some women experience cramping and spotting of blood in this week while implantation is taking place, and they possibly will mistake this for a period, as it often occurs around the time their monthly period is due.

hCG is the hormone that is measured in pregnancy tests. This week a pregnancy test will most likely be able to detect your pregnancy! hCG also causes symptoms of pregnancy, which may appear this week.

Fatigue, tingling and aching breasts, or nausea might direct you to believe your period will be starting any day since the first pregnancy symptoms resemble premenstrual syndrome (PMS). However, by the end of this week, your expected period will not take place. Your pregnancy is certainly well on its way!