pregnancy

pregnancy The state of carrying a developing embryo or fetus within the female body. Pregnancy can be indicated by positive results on an over-thecounter urine test and confirmed through a blood test, an ultrasound, or detection of a fetal heartbeat. Pregnancy lasts for about 40 weeks, measured from the date of the woman’s last menstrual period. It is conventionally divided into three trimesters, each roughly 3 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 firsttrimester fetus can survive outside the womb, even with the best hospital care; its systems are simply too undeveloped. In the first trimester, some women experience morning sickness. During the second trimester, the physical parts of the fetus 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 problems may emerge later. In the third trimester, the fetus enters the final stage of preparation for birth. It increases rapidly in weight, as does the mother. Swelling of the ankles, back pain, and balance problems are sometimes experienced during this time. Pregnancy ends when the birth process begins. See also acute fatty liver of pregnancy; birth; birth defect; conception; eclampsia; ectopic pregnancy; fetal alcohol effect; fetal alcohol syndrome; HELLP syndrome; hyperemesis gravidarum; preeclampsia; pregnancy, tubal; prenatal care; prenatal development; teratogen.