1. School of Medical Technology, Jiangsu College of Nursing, Huai'an, Jiangsu 22300, P.R. China
2. Department of Ultrasonography, Huai'an Maternity and Child Health Care Hospital, Huai'an, Jiangsu 223002, P.R. China
3. Clinical Medical Laboratory, Huai'an Maternity and Child Health Care Hospital, Huai'an, Jiangsu 223002, P.R. China