Last menstrual period ultrasound dating transvaginal
Determining the Date of Conception Because the human egg is capable of fertilization for only 12 to 24 hours after ovulation the date of ovulation may be taken as being the date of conception.
Clinical management guidelines for obstetrician-gynecologists. In cases where the date of conception is known precisely, such as with in vitro fertilization, the EDD is calculated by adding 266 days to the date of conception. American College of Obstetricians and Gynecologists. Ultrasound uses the size of the fetus to determine the gestational age (the time elapsed since the the first day of the last menstrual period). Otherwise "..avoid missing a situation of early intrauterine growth restriction in one twin, most experts agree that the clinician may consider dating pregnancy using the larger fetus." [22,23]. Observed Gestational Age at Delivery The table below shows the average age of infants delivered in the United States according to the number of fetuses being carried (plurality) . Savitz DA, Terry Jr JW, Dole N, et al: Comparison of pregnancy dating by last menstrual period, ultrasound scanning, and their combination. The timing of the "fertile window" in the menstrual cycle: day specific estimates from a prospective study BMJ 2000; 321: 1259-1262. Effects on the probability of conception, survival of the pregnancy, and sex of the baby.
Timing of sexual intercourse in relation to ovulation.
The American College of Obstetricians and Gynecologists.
Berghella V, et al., Does transvaginal sonographic measurement of cervical length before 14 weeks predict preterm delivery in high-risk pregnancies?
The due date may be estimated by adding 280 days ( 9 months and 7 days) to the first day of the last menstrual period (LMP). The accuracy of the EDD derived by this method depends on accurate recall by the mother, assumes regular 28 day cycles, and that ovulation and conception occurs on day 14 of the cycle.
Use of the LMP to establish the due date may overestimate the duration of the pregnancy, and can be subject to an error of more than 2 weeks [5-7].
303, February 2014 Society of Obstetricians and Gynaecologists of Canada.