Definition of Pregnancy

Pregnancy: The state of carrying a developing embryo or fetus within the female body. This condition can be indicated by positive results on an over-the-counter urine test, and confirmed through a blood test, ultrasound, detection of fetal heartbeat, or an X-ray. Pregnancy lasts for about nine months, measured from the date of the woman's last menstrual period (LMP). It is conventionally divided into three trimesters, each roughly three months long.

The most important tasks of basic fetal cell differentiation occur during the first trimester, so any harm done to the fetus during this period is most likely to result in miscarriage or serious disability. There is little to no chance that a first-trimester fetus can survive outside the womb, even with the best hospital care. Its systems are simply too undeveloped. This stage truly ends with the phenomenon of quickening: the mother's first perception of fetal movement. It is in the first trimester that some women experience "morning sickness," a form of nausea on awaking that usually passes within an hour. The breasts also begin to prepare for nursing, and painful soreness from hardening milk glands may result. As the pregnancy progresses, the mother may experience many physical and emotional changes, ranging from increased moodiness to darkening of the skin in various areas. During the second trimester, the fetus undergoes a remarkable series of developments. Its physical parts become fully distinct and at least somewhat operational. With the best medical care, a second-trimester fetus born prematurely has at least some chance of survival, although developmental delays and other handicaps may emerge later. As the fetus grows in size, the mother's pregnant state will begin to be obvious. In the third trimester, the fetus enters the final stage of preparation for birth. It increases rapidly in weight, as does the mother. As the end of the pregnancy nears, there may be discomfort as the fetus moves into position in the woman's lower abdomen. Edema (swelling of the ankles), back pain, and balance problems are sometimes experienced during this time period. Most women are able to go about their usual activities until the very last days or weeks of pregnancy, including non-impact exercise and work. During the final days, some feel too much discomfort to continue at a full pace, although others report greatly increased energy just before the birth. Pregnancy ends when the birth process begins.

See also acute fatty liver of pregnancy; ectopic pregnancy; fetal alcohol syndrome; fetal alcohol effect; hyperemesis gravidarum; preeclampsia; pregnancy, tubal; prenatal care; prenatal development; birth defect; teratogen.

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