1Morin L, Lim K. Ultrasound in twin pregnaneies [J]. J Obstet Cynaecol Can, 2011,33 (6) : 643-656.
2Vayssirre C, Benoist G, Blondel B, et al. Twin pregtlancies: guidelines for clinical practice from the French College of Gyn- aecologists and Obstetricians (CNGOF) [ J]. Eur J Obstet Gyne- col Reprod Biol,2011,156( 1 ) : 12-17.
3Bromley F, Band B, Benacerraf D. Using the number of yolk sacs to determine amnionicity in early first trimester monochorionic twins[J]. J Ultrasound Med, 1995,14(6) :415-419.
4Dias T, Weerasinghe A, Amarathunga P, et al. Twin pregnancy chorionicity determination in a tertiary care setting [J]. Ceylon Med J, 2013,58(4) : 170-172.
5Multiple pregnancy:the management of twin and triplet pregnan- cies in the antenatal period, 2011, London : National Collaborat- ing Centre for Women's and Children's Health [EB/OL]. http:// www, niee. org. uk/guidance/qs46.
6Benoist MP, Gand M, Herlieoviez G. Diagnosis of ehorioniei-ty[ J ]. J Gyneeol Obstet Biol Reprod, 2009,38(8 S) :S18- S30.
7Butt K, Lira K. Determination of gestational age ])y ultra- sound[J ]. J Obstet Gynaeeol Can, 2014,36(2): 171-183.
8Kalish RB, Thaler HT, Chasen ST, et al. First-and second-tri- mester uhrasound assessment of gestational age [J]. Am J Ob- stet Gyneeol, 2004, 191 ( 3 ) : 975-978.
10Weissmann-Brenner A, Weisz B, Achirnn R,et al. Can discor- dance in CRL at the first trimester predict birth weight discor- dance in twin pregnancies? [ J ]. J Perinat Med, 2012,40 (5) : 489-493.
