Congrats on the bundle of joy....sound advice would be to check with a doctor but we will all chip in too since you asked. It occured to me that as your body prepares to give birth your ligaments (esp. those in the low back and pelvis) will begin to slacken, although this does vary from person to person as to exact timing and degree. The thought being that cycling in anything remotely aerodynamic position may just be too painful and lead to other injuries. Of course trauma is probably the biggest worry and if you are going to ride make sure to carry something that states very clearly and in an easy to find place that you are pregnant. God forbid you do have an accident that leaves you out cold, but if so, the EMS personel NEED to know that you are an expecting mother. Good luck and stay active even if it isn't cycling!