At present the Centre for Disease Control in the United States recommends universal routine screening early in pregnancy for all pregnant women, on an 'opt-out' basis.8.
目前，美国疾病控制中心建议在选择退出的基础上，对怀孕初期的妇女进行普遍的常规检查。
2
Of 13 population clusters, seven were randomly allocated to three rounds of screening between 1996 and 2004, while standard care was provided in six (control arm).