3Palomaki GE, Neveux LM, Knight GJ, et al. Maternal serumintegrated screening for trisomy 18 using both first - and second - trimester markers [ J ]. Prenat Diagn ,2003,23: 243 - 247.
4Meier C, Huung T, Wyatt PR, et al. Accuracy oftrisomy 18 screening using the second--trimester triple test [ J ]. Prenat Diagu, 2003,23 : 443 - 46.