Pregnancy Calendar Week 4

Week 4

What's Happening to My Body?

In this fourth week of pregnancy, your baby is two weeks old and is just a tiny speck, less than a millimeter long.

But significant changes are taking place. The 150-cell embryo, or blastocyst, is now imbedded in your uterine wall. The placenta (which mediates the exchange of food between mother and baby) will eventually develop from the outer layer of blastocyst cells, but your blood has already begun to nourish the developing cells. The yolk sac forms, which will produce the baby's blood cells until about the 11th week of development.

The chorionic villi, tiny finger-like projections on the placenta, begin to appear. By the end of Week 5, fetal blood will circulate through the villi and take nutrients and oxygen from your blood; carbon dioxide and other waste products will pass from the fetal blood to yours.

Are We Having Fun Yet?

You may notice that you've missed your period, but if your periods are irregular, this may not be a sure sign for you. Your tender breasts (yikes, even a bra rubs you the wrong way), queasy stomach, bitchy mood and constant trips to the bathroom to pee might be hints that something significant is happening.

The scale probably won't tell you, because you haven't begun to gain weight, but you might fall asleep standing on the scale -- or doing anything else, for that matter. Fatigue is common in early pregnancy. You may also feel a slight low cramping similar to menstrual cramps. This means that your uterus is enlarging. You may notice a metallic taste and increased saliva in your mouth. Your heightened sense of smell might make you feel qualified to join the drug-sniffing dogs at the airport.