3Andersen HF, Nugent CE, Wanty SD, et al. Prediction of risk for pre-term delivery by ultrasonographic measurement of cervical length [J]. Am J Obstet Gynecol,1990, 163:859 -867.
4Iams JD, Goldenberg RL, Meis PJ, et al. The length of the cervix and the risk of spontaneous premature delivery [ J ]. N Engl J Med, 1996, 334 (2) : 567 - 572.
5Cook CM, Ellwood DA. The cervix as a predictor of preterm delivery in at- risk woman [ J]. Ultrasound Obstet Gynecol,2000,15:109 - 113.
6Gunby J, Daya S. Assisted rep roductive technologies (ART) in Canada: 2001 results from the Canadian ART register [ J]. Fertil Steril, 2005,84 : 590-599.
7Society for Assisted Reproductive Technology. Assisted reproductive technology in the United States:2000 results generated from the American Society for Reproductive Medicine/Society for Assisted Reproductive Technology Registry [ J ]. Fertil Steril, 2004,81 : 1207-1220.
8Chou HC, Tsao PN, Yang YS, et al. Neonatal outcome of infants born after in vitro fertilization at National Taiwan University Hospital[ J ]. J Formos Med Assoe,2002,101: 203 -205.
9Putternan S, Figueroa R, Garry D, et al. Comparison of obstetric outcomes in twin pregnancies after in vitro fertilization ,ovarian stimulation and spontaneous conception [ J ]. Matern Fetal Neonatal Med, 2003,14 : 237-240.
10Dhont M, De Sutter P, Ruyssinck G, et al. Perinatal outcome of pregnancies after assisted reproduction., a casecontrol study[ J]. Am J Obstet Gynecol, 1999,181:688- 695.
