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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 earlier age at delivery of multiple gestations is a reflection of the increased incidence of preterm labor and obstetric intervention for complications such as preeclampsia, abruptio placentae, fetal growth restriction, and increased risk for stillbirth that occurs as the number of fetuses increases [30-33]. Mongelli M, Wilcox M, Gardosi J.: Estimating the date of confinement: ultrasonographic biometery versus certain menstrual dates.
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.
Time of implantation of the conceptus and loss of pregnancy.
Twins When a twin pregnancy is the result of in vitro fertilization determination of gestational age should be made from the date of embryo transfer. Clinical management guidelines for obstetricians-gynecologists. Number 55, September 2004 (replaces practice pattern number 6, October 1997).
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].
Clinical management guidelines for obstetrician-gynecologists.
Number 4, May 1999 (replaces educational bulletin Number 147, October 1990).
The American College of Obstetricians and Gynecologists recommends that ultrasound-established dates should take preference over menstrual dates when the discrepancy between ultrasound dating and LMP is "Because of the risk of redating a small fetus that may be growth restricted, management decisions based on third-trimester ultrasonography alone are especially problematic; they need to be guided by careful consideration of the entire clinical picture and may require closer surveillance, including repeat ultrasonography to ensure appropriate interval growth." . Birth weight from pregnancies dated by ultrasonography in a multicultural British population.