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In 2006, the number of live births in the U.S. totaled nearly 4.3 million, the largest number since 1961. The percentage of women who received prenatal care in the first trimester decreased and the percentage of women with late or no prenatal care increased in 2006.1 These trends are concerning, as ongoing prenatal care is associated with improved pregnancy outcomes. Recent attention is focusing on improving women’s health before conception, in addition to prenatal care, to improve pregnancy outcomes. Many of the medical conditions, environmental exposures, personal behaviors, and psychosocial risks that are associated with negative pregnancy outcomes can be identified and modified or eliminated before conception.2

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Regardless of the chief complaint, the possibility of pregnancy must be considered in every woman of reproductive age who presents to the ED. The use of barrier methods, contraceptives, or even sterilization does not guarantee pregnancy prevention. Unintended pregnancies occur because of lack of contraception, imperfect use of contraception, and contraceptive failure. Forty eight percent of unintended pregnancies occur in a month during contraception.3 The failure rates of barrier methods are variable. Although the failure rate with compliant use of oral contraceptives is <1 per 100, nearly 30% of women who rely solely on oral contraceptives to prevent pregnancy are not consistently compliant.4 During the first 5 years of therapy with levonorgestrel implants, the annual pregnancy rate is 0.8 per 100. The failure rate of implants increases with time.5 Tubal sterilization is a more reliable means of pregnancy prevention, with the failure rate depending on the surgical technique. Partial salpingectomy has a failure rate of only 0.75%.6

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Gravidity denotes the total number of pregnancies regardless of duration and outcome. Parity denotes the number of pregnancies completed to delivery during the viable period. Parity is not increased for a pregnancy resulting in multiple births or decreased for a stillborn fetus. Notation of obstetric history typically lists the gravidity (G) followed by the appropriate number and then the parity (P) followed by the appropriate number. After the gravidity and parity, there may be a listing of the number of term deliveries, preterm deliveries, abortions, and living children. The latter four numbers are separated by hyphens and listed in parentheses. For example, the obstetric history of a woman during her seventh pregnancy who has had four term deliveries, one preterm delivery, and one abortion and has five living children is abbreviated G7 P5 (4-1-1-5).

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The duration of pregnancy is approximately 40 weeks. By convention, gestational age (or menstrual age) is calculated from the first day of the last normal menstrual period. Ovulation normally occurs around day 14 of the menstrual cycle. After ovulation, the ovocyte remains capable of being successfully fertilized for up to 12 hours. Fertilization usually takes place in the ampulla of the oviduct. The fertilized ovocyte (zygote) transforms into the morula as it travels toward the uterus. By 6 days after fertilization, it enters the uterine cavity and implants in the endometrium. Weeks 2 through 8 (after fertilization) are the embryonic period. Week 9 is ...

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