3Offerdal K, Jebens N, Blaas HG, et al. Prenatal ultrasound detection of talipes equinovarus in a non-selected population of 49 314 deliv- eries in Norway [J]. Ultrasound Obstet Gynecol, 2007, 30:838-844.
4Salomon LJ, Alfirevic Z, Berghella V, et al. Practice guidelines for performance of the routine mid-trimester fetal ultrasound scan[J]. Ultrasound Obstet Gynecol, 2011, 37:116-126.
6Zalel Y, Aehiron R, Kivilevitch Z. Sonogmphic visualization of the middle phalanx of the fetal 6fth digit between 13 and 17 weeks of gestation[J]. Ultrasound Obstet Gynecol, 2007, 30:263-265.
9Baronciani D, Scaglia C, Corchia C, et al. Ultrasonography in pregnancy and fetal abnormalities: screening or diagnostic test.? IPIMC 1986-1990 register data. Indagine Policentrica Italiana sulle Malformazioni Congenite[ J ].Prenat Diagn, 1995, 15(12): 1101-1108.
10Chitty L S, Hunt G H, Moore J, et al. Effectiveness of routine ultrasonography in detecting fetal structural abnormalities in a low risk population[J].BMJ, 1991, 303(6811): 1165-1169.
