Pregnancy dating scan accuracy
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.
Before the advent of pregnancy tests and ultrasonography, quickening was often the method by which a suspected pregnancy was confirmed; however, at present, it has little diagnostic value.
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.
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.
More accurate results can be obtained by using computer software or web-based online calculators (eg, as found online at the Gestation Network).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.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.