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Fetal right ventricular contraction and relaxation times at 11-13 weeks' gestation by speckle tracking imaging.
Persico N, Fabietti I, Baffero G, Fedele L, Nicolaides KH.
Ultrasound Obstet Gynecol 2014;43:284-90. pdf -
The 11-14 week scan.
Nicolaides KH, Heath V, Liao AW.
Baillieres Best Pract Res Clin Obstet Gynaecol 2000;14:581-94.