dear ***:
I would like to know if I could ask for a casual leave of absence for (写上你要请假的天数) day on （写上要请假的具体日期）, （表明是周几）.
The reason for my absence is that my wife is pregnant and I have to company her to go to hospital to do the antenatal care.
Concerning my workload: As (写上请假的那天是周几) is not as busy as the other weekdays, I think a one-day leave this 周几 may be the best solution. I apologize for the inconvenience my absence from work may cause.
Thanks. I will call you at (写上你想要得到老板的答复的时间). or you can call me at any time.
希望能够帮到你，如果你是要写电邮的话，还要注意电邮的格式，大致如下：
To：假条是递给谁的
From：请假人
Date：写假条的日期(注意不是请假的日期)
Subject：写上请假字样