pregnancy (preg) /preg′nənsē/ [L, praegnans, pregnant] , the gestational process, comprising the growth and development within a woman of a new individual from conception through the embryonic and fetal periods to birth. Pregnancy lasts approximately 266 days (38 weeks) from the day of fertilization, but it is clinically considered to last 280 days (40 weeks; 10 lunar months; 9⅓ calendar months) from the first day of the last menstrual period. The expected date of delivery (EDD) is calculated on the latter basis even if a woman’s periods are irregular. If a woman is certain that coitus occurred only once during the month of conception and if she knows the date on which coitus occurred, the EDD may be calculated as 266 days from that date. Pregnancy begins after coitus at or near the time of ovulation (usually about 14 days before a woman’s next expected menstrual period). Of the millions of ejaculated sperm cells, thousands reach the female ovum in the outer end of the fallopian tube, but usually only one penetrates the egg for union of the male and female pronuclei and conception. The zygote, genetically a unique entity, begins cell division as it is transported to the uterine cavity, where it implants in the uterine wall. Maternal and embryological elements together form the beginnings of the placenta, which grows into the substance of the uterus. The placenta functions in maternal-fetal exchange of nutrients and waste products, although the maternal and fetal bloods do not normally mix. The conceptus is in some aspects like a foreign graft or transplant in the mother. Although an immune response is normally activated in the mother, all of her tissues and organs undergo change, many of them profound and some of them permanent. Cardiac output increases 30% to 50% in pregnancy. The increase begins at about the sixth week, reaches a maximum about the sixteenth week, declines slightly after the thirtieth week, and rapidly falls off after delivery. It returns to prepregnancy level about the sixth week after delivery. The stroke volume of the heart increases, and the pulse rate becomes more rapid: Normal pulse rate in pregnancy is approximately 80 to 90 beats/min. Blood pressure may drop slightly after the twelfth week of gestation and return to its usual level after the twenty-sixth week. The circulation of blood to the pregnant uterus near term is about 1 L/min, requiring about 20% of the total cardiac output. Total blood volume also increases in pregnancy; plasma volume increases more than red cell volume, and this results in a drop in the hematocrit, caused by dilution. The number of white blood cells increases: The normal white blood cell count in pregnancy is often above 15,000/mL. ▪ PATIENT CARE CONSIDERATIONS: The emotional experiences of pregnancy, as reported by pregnant women, are normal and healthy, but extraordinary. A pregnant woman is “herself,” but in a very unfamiliar way. She has a sense of heightened function and expectancy. Being keenly aware of the rapid and inevitable changes her body is undergoing, she is more intensely interested in herself. Her concern for the perfection of her baby, her anticipation of the exertion of labor, and her contemplation of the new or expanded responsibilities of motherhood all serve to intensify her emotional tone.
