IF your expected date of delivery falls in mid-December, you can go on pre-natal leave of 8 weeks probably from mid-October. In the mean time, it is imperative that you should be free from unnecessary employment stress and strain created by your immediate superior. Better you can ventilate your grievances formally to the Corporate HR-Head through proper channel which would make him correct his approach.
As i read above about you. thats your Manager is forcing you to do all hectic work not to giving you light work and help you any more . i would suggest you that please take deep breath and have patience to fight with him legally. First of all you can inform to your HR about you pregnancy and planning to take leaves in near future. and inform them by documenting about rudeness of your Manager. Because this time he is trying to create pressure on you to put your papers down. Dont be panic, be confident and go against him legally. he can not do anything until you are not giving any chance to him.