4Grannum PA. The ultrasounic changes in the maturing placental and their relation to fetal pulmonic mature[J]. Am J Obstet Gynecol, 1979, 133: 915
5Weiner Z, Farmakides G, Barnkard Y, et al. Doppler study of the fetal cardiac function in prolonged pregnancies[J]. Obstet Gynecol ,1996, 88:200
6Wing DA, Fishman A, Gonzalez C, et al. How frequently should the amniotic fluid index be performed during the course of antepartum testing?[J]. Am J Obstet Gynecol, 1996, 174:33-36
