If you are in the first 14 weeks of your pregnancy, you may be asked to have a full bladder for your scan. This allows the water in the bladder to be used as a clear "viewing window" so the baby can be seen. After 14 weeks, having a full bladder when you come for your appointment is not necessary .
上面是我在哈密尔顿这里的检查中心网站上看到的