Dating pregnancy with ultrasound
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]. 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. Number 9, October 1999 (replaces Technical Bulletin Number 188, January 1994). Twin pregnancy: the role of ultrasound in management. The tendency for multiple gestations to be delivered earlier than singleton pregnancies should not be interpreted that multiples should be assigned an earlier estimated due date. A full term pregnancy is considered to be 39 to 40 6/7 weeks regardless of the number fetuses being carried . Chervenak FA, Skupski DW, Romero R, et al: How accurate is fetal biometry in the assessment of fetal age?
The accuracy of the ultrasound estimate of the gestational age varies according to the gestational age. Multifetal gestations: twin, triplet, and higher-order multifetal pregnancies. Page JM, The risk of stillbirth and infant death by each additional week of expectant management in twin pregnancies. Doppler Ultrasonography The fetal heart can be heard using Doppler ultrasound by 10 to 12 weeks in most patients . Savitz DA, Terry JW Jr, Dole N, Thorp JM Jr, Siega-Riz AM, Herring AH. The gestational age should ,therefore, be at least 10 to 12 weeks if fetal heart tone are heard. Kramer MS, Mc Lean FH, Boyd ME, Usher RH: The validity of gestational age estimation by menstrual dating in term, preterm and postterm gestations. Comparison of pregnancy dating by last menstrual period, ultrasound scanning, and their combination.