If you se something you really really like then I can't see any thing wrong with buying it. I got a couple of little gender neutral suits an bunny rugs cos I was feeling particularly clucky one day. We didn't buy anything major till I was about 16 weeks PG though.
As some of the others have said if you have a loss it will upset you greatly to have it all sitting there.

Also another thing to consider is that trends change and new things come out all the time and you may regret that you didn't wait. There will also be another bargain around the corner too if that is a motivation. Baby shops are incredibly competitive and will match prices.

You could always make a special savings account and put a little bit away each week so the cash is there waiting for when the time comes.