胎儿常见染色体异常与开放性神经管缺陷的产前筛查与诊断技术标准 第1部分:中孕期母血清学产前筛查胎儿常见染色体异常与开放性神经管缺陷的产前筛查与诊断技术标准 第1部分:中孕期母血清学产前筛查technology standard of prenatal screening and diagnosis for fetal common chromosomal abnormalities and open neural tube defects Part 1: Maternal serum prenatal screening in second trimester