I know this is old, and OP has made a decision but I wanted to post anyway for others who are wondering. I have kept mine in so far (35 weeks), I switched from a normal metal barbell to my maternity one at about 27/28 weeks. I got a pack that had a really long bar, cut it in half and then took one of the halves and cut that in a 2/3 and 1/3 piece. At first I used the smaller pieces and as my belly has grown I have switched to the larger ones.
So far I haven't had any issues other than a little discoloration but that I'm pretty sure was due to when it got infected because before I switched from the metal to the plastic my shirt snagged on the bar and nearly ripped it out of my stomach, causing a tear, and after lotion got in the cut it got infected...so I advise you be really careful as your belly grows as the whole snagging thing can become an issue, but plastic is much more forgiving than metal so whenever I do snag with the maternity bar it's not nearly as bad as when I had the metal bar.