Pregnancy physiology relates to all physical aspects and changes within the body that take place during pregnancy. This generally includes all elements of the maternal pregnancy process, as well as all stages of fetal development. Pregnancy physiology may refer to the birthing process as well.
Changes in pregnancy will vary from person to person, and stages of development are divided into categories known as the first trimester, second trimester and third trimester of pregnancy. The first trimester occurs during the first 12 weeks of pregnancy. One common occurrence in maternal pregnancy physiology is morning sickness, especially during the first trimester. Morning sickness is a common term for nausea that occurs early in the morning. Not every pregnant woman will experience symptoms of morning sickness, however.
During the first trimester, a pregnant woman may experience tender or aching breasts, constipation, or hemorrhoids. Irritability or depression are other symptoms many women experience during the early stages of pregnancy. During the second and third trimesters, frequent urination may also occur. Some women experience swollen ankles during pregnancy, although this may be related to other physical issues.
Maternal weight gain is a major aspect of pregnancy physiology. Depending upon the woman's body frame and height, she may gain anywhere from 25 to 65 pounds (11 to 29 kilograms). The pregnant woman may gain up to 6 pounds (2.72 kilograms) in body fluid. At full term, the average fetus weight is generally 7 pounds (3.17 kilograms).
A vital aspect of fetal physiology is heart rate, which increases during the stages of pregnancy. At four or five weeks, a human fetus will have an average heart rate of about 100 beats per minute. When a fetus experiences a dangerously low heart rate, this condition is known as bradycardia. After birth, the average newborn heart rate is approximately 130-135 beats per minute.
Pregnancy physiology also refers to changes that occur within major bodily organs. Changes within the cardiovascular system and pulmonary system are also examined in the study of pregnancy physiology. The gastrointestinal system of many women may also be affected by changes that occur during pregnancy.
Many books have been written on the subject of pregnancy physiology. Some are in medical textbook form, which can be helpful for students studying medicine. Other publications include simple guidelines for pregnant women to follow and refer to during all stages of pregnancy.