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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).
Pregnant women should be counselled that only 4% of all babies are born precisely on the estimated date of confinement.
Tape measurement of the symphysis-fundus height may be useful up to 28-30 weeks' gestation, beyond which it becomes too inaccurate for dating.
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.
Basing GA on the LMP tends to result in an overestimation.
The 95% confidence interval of menstrual dates is -27 to 9 days.
Infants born before 37 completed weeks' gestation are deemed preterm, whereas those born after 42 weeks' are considered post-term.
In normal pregnancies, the length of gestation is minimally affected by maternal characteristics.
In rare cases, the date of coitus is known, and this may be useful in calculating the length of pregnancy.For related information, see Medscape's Pregnancy Resource Center.Gestational age (GA) refers to the length of pregnancy after the first day of the last menstrual period (LMP) and is usually expressed in weeks and days. Conceptional age (CA) is the true fetal age and refers to the length of pregnancy from the time of conception.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 size of the uterus can be assessed by pelvic examination or by abdominal palpation.