I really like this type of neckline.  I used it for Pigg#2’s Easter Dress and just seem to be drawn back to it over and over.  
I wanted to make one for myself.  It needed to match a shirt underneath since I’m a sleeve type of girl and I wanted it to match a skirt I have (not pictured).  I came up with this.   Hopefully I can wear it after the baby with a belt and it will still look good.
 I pulled out an XL white long sleeve t-shirt from my stash.
I used another maternity shirt to help me with the width and length of the shirt.
And cut out a front and back.  With the front being a bit wider.
 The neck opens on one side with the button.
 Another pic because I like the button.
 And gathered in the back as well.
I’m pleased and hope it gets some good use.