During the second trimester of pregnancy, the mother’s heart at rest is working 30 to 50 percent harder. Most of this increase results from a more efficiently performing heart, which ejects more blood at each beat. Heart rate may increase up to 15 to 20 percent during pregnancy. It’s not uncommon to approach 90 to 100 beats per minute in the third trimester. Blood volume increases progressively during pregnancy until the last month. The volume of plasma increases 40-50 percent and red blood cell mass 20-30 percent, creating a need for increased iron and folic acid intake.
For pregnant women, the level of estriol in the blood is used in a maternal serum triple or quadruple screening test . In most cases, these tests are done between 15 and 20 weeks of pregnancy. They check the levels of three or four substances in a pregnant woman's blood. The triple screen checks alpha-fetoprotein (AFP), human chorionic gonadotropin (hCG), and a type of estrogen (unconjugated estriol, or uE3). The quad screen checks these substances and the level of the hormone inhibin A. The levels of these substances-along with a woman's age and other factors-help the doctor figure out the chance that the baby may have certain problems or birth defects .