早孕期是推算胎龄比较合适的时期,因为①早期妊娠的生物变异性较小,此时个体基因或环境因子对胎儿过大或过小的影响尚不明显。②每单位时间的生长率远较后期妊娠为大。在早孕时科学地推算胎龄,以采用超声检查的方法最为适宜。对于有经验的超声工作者,这种方法相当准确。操作人员根据妊娠囊与子宫体积的比例和个人经验加以判断:孕5周时开始在宫腔内可见妊娠囊的环形结构;7周后妊娠囊逐渐增大,8周时 Early pregnancy is estimated gestational age more appropriate period, because early pregnancy less biological variability, when the individual genes or environmental factors on the fetus is too large or too small, the impact is not yet obvious. ② the growth rate per unit of time is much larger than the late pregnancy. In early pregnancy scientifically estimated gestational age, the most appropriate way to use ultrasound. This method is quite accurate for experienced sonographers. The operator according to the gestational sac and uterine volume ratio and personal experience to be judged: 5 weeks pregnant began in the uterine cavity of the gestational sac can be seen ring structure; gestational sac gradually increased after 7 weeks, 8 weeks