Obstetric dating and assessment

The date of the first documented positive pregnancy test and the beta-human chorionic gonadotropin (b HCG) level may help ascertain the minimum gestational age.In women who conceived following assisted reproduction techniques, the date of embryo transfer is known and may date the pregnancy accurately.

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Knowing the date of the first positive pregnancy test result allows the calculation of a minimum GA. For example, if the test was performed 4 weeks ago and the test is known to return positive results as early as 1 week after conception, then the minimum conceptional age (CA) would be 5 weeks (GA, 5 2 = 7 wk of amenorrhea).

This information can be useful in clinical practice if the test finding has been documented by a health care professional.

Not infrequently, practitioners are called upon to manage pregnancies resulting from in vitro fertilization or intrauterine insemination.

The GA of pregnancies resulting from in vitro fertilization can be precisely calculated from the time of embryo replacement; however, conception may be delayed for a few days in pregnancies resulting from intrauterine insemination.

The estimation of pregnancy dates is important for the mother, who wants to know when to expect the birth of her baby, and for her health care providers, so they may choose the times at which to perform various screening tests and assessments,such as serum screening, assessment of maturity, and induction of labor for postdate pregnancies.

The 3 basic methods used to help estimate gestational age (GA) are menstrual history, clinical examination, and ultrasonography.The expected date of delivery (EDD) is one of the earliest pieces of information a pregnant woman requests once pregnancy is confirmed.In order to calculate the EDD, the practitioner must know the median length of normal pregnancy and the last menstrual period (LMP) or ultrasonographic estimation of gestational age (GA).The fallacy in this assumption is that the time of ovulation varies greatly in relation to the menstrual cycle, both from cycle to cycle and individual to individual.Basing GA on the LMP tends to result in an overestimation.The perception of fetal movement by the patient, often referred to as quickening, is a relatively late sign of pregnancy, usually occurring at 19-21 weeks' gestation in nulliparous women and 17-19 weeks' in multiparous women.

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