Gestational dating ultrasound

Therefore, giving a range for the likely date of birth (eg, EDD -2 weeks to EDD 1 week) is more useful.Infants born before 37 completed weeks' gestation are deemed preterm, whereas those born after 42 weeks' are considered post-term.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).

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In patients who have had ovulation induction, calculate GA from the day of human chorionic gonadotropin administration.

The size of the uterus can be assessed by pelvic examination or by abdominal palpation.

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.

For example, with an LMP beginning on June 15, the EDD will be March 22 of the following year. These consist of an outer wheel that has markings for the calendar and an inner, sliding wheel with weeks and days of gestation.

They facilitate the estimation of GA and the calculation of the EDD.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 terminology does vary geographically and over time, and it may need clarification if not explicitly defined in relevant articles.Size can be misleading in the presence of multiple pregnancy, uterine fibroids, or a full bladder.Tape measurement of the symphysis-fundus height may be useful up to 28-30 weeks' gestation, beyond which it becomes too inaccurate for dating.In normal pregnancies, the length of gestation is minimally affected by maternal characteristics.

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