羊水有保护母体及胎儿的作用。羊水的来源、量及组成随孕期发生变化。妊娠早期主要由母体血清由胎膜滤过而成,中晚期主要来源于胎儿尿液。羊水量在产时可以直接测量,以往产前靠触诊子宫以估计羊水量,准确性极差。B型超声检查(以下简称B超)根据羊膜腔暗区大小的测定,可较准确地估计产前的羊水量,能对异常者及时作出处 Amniotic fluid to protect the mother and fetus role. Amniotic fluid source, amount and composition change with pregnancy. Early pregnancy mainly by the maternal serum from the fetal membrane filtration, mainly in the late fetal urine. Amniotic fluid output can be measured directly in the past, past prenatal palpation of the uterus to estimate the amniotic fluid volume, poor accuracy. B-mode ultrasound (hereinafter referred to as B-ultrasound) based on the determination of the size of the amniotic dark area can be more accurately estimated prenatal amniotic fluid volume, abnormalities can be promptly made