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Figure

Mechanism that preserves the uterine lining during early pregnancy.

Secretion of hCG continues at a high level for about two months, then declines to a low level by the end of four months. Although the corpus luteum persists throughout pregnancy, its function as a source of hormones becomes less important after the first three months (first trimester), when the placenta secretes sufficient estrogens and progesterone (fig. 22.38).

Detecting hCG in a woman's urine or blood is used to confirm pregnancy. The level of hCG in a pregnant woman's body fluids peaks at fifty to sixty days of gestation, then falls to a much lower level for the remainder of pregnancy. Later on, measuring hCG has other uses. If a woman miscarries but her blood still shows hCG, fetal tissue may remain in her uterus, and this material must be removed. At the fifteenth week of pregnancy, most women have a blood test that measures levels of three substances produced by the fetus — alpha fetoprotein, estriol (one of the estrogens), and hCG. If alpha fetoprotein and estriol are low but hCG is high, the fetus may have an extra chromosome, with severe effects on health.

3 4 5 6 Months of pregnancy

Figure

Relative concentrations of hCG, estrogens, and progesterone in the blood during pregnancy.

3 4 5 6 Months of pregnancy

Essentials of Human Physiology

Essentials of Human Physiology

This ebook provides an introductory explanation of the workings of the human body, with an effort to draw connections between the body systems and explain their interdependencies. A framework for the book is homeostasis and how the body maintains balance within each system. This is intended as a first introduction to physiology for a college-level course.

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