Ultrasonography alone does not determine if a pregnancy has Down syndrome or other chromosomedisorders;
只做超声检查不能确定胎儿有唐氏综合征或其他染色体病变；
2
Female mosaicism of the X chromosome has major implications for human health and disease and is the leading cause of female protection from X-linked genetic disorders.
女性作为X染色体的杂合子在人类的健康与疾病中及重要作用，并可避免X连锁遗产性疾病在女性中发生。
3
Currently, we are able to perform PGD for many genetic conditions including single gene disorders and chromosome abnormalities.