The first trimester of pregnancy is often considered the second most exciting time during pregnancy. Birth is, of course, the most exciting time. During the first trimester of pregnancy, women find out they are pregnant, attend the first prenatal appointment and notice a long list of changes in their body. Understanding what happens in the body during the first trimester of pregnancy is important as some changes may not feel the way a pregnant woman expected.

In the Beginning of the First Trimester of Pregnancy

Even before the pregnancy test reads positive, there are changes happening during the first trimester of pregnancy. During ovulation the egg is released and the corpus luteum signals the release of progesterone. Progesterone causes the lining of the uterus to thicken and engorge with blood. When fertilization occurs, the fertilized egg implants in the thicker lining and starts to grow immediately. Human chorionic gonadotropin (HCG) is released keeping the corpus luteum alive for the duration of the pregnancy. HCG is the hormone that turns a pregnancy test from negative to positive.

What do these changes in the first trimester of pregnancy mean for a pregnant woman?

While women do not physically feel the egg and sperm meet, they may feel the egg implanting in the uterus. Some women report feeling a small cramp and a bit of spotting. This spotting is typically associated with the upcoming menstrual cycle when it is actually implantation spotting.

So, the hormones estrogen, progesterone and HCG are flooding the body at this point. From the first moments after conception, the body kicks into gestational mode. These hormones are to blame for many of the pregnancy induced symptoms women feel in the first trimester of pregnancy including nausea, vomiting and fatigue. Some women actually feel like they have a touch of the flu for most of the first trimester of pregnancy. Hormones are not selective. They cannot increase in the bloodstream and selectively attend to only the needs of the fertilized egg (zygote and later fetus). When progesterone levels are rising, the pregnant woman is feeling the effects as symptoms.

The human body is highly adaptive, however, so after the first trimester of pregnancy, things should go back to normal for a while. The morning sickness and tender breasts may be fading a bit or the pregnant woman may just get used to feelings and symptoms the hormone surge caused. For many women, the first trimester of pregnancy does not last very long at all because many pregnancies are not detected until after the 6th week of gestation. That leaves only 6 weeks to conquer the first trimester of pregnancy before moving into the period of growth and more changes.

First Trimester