[Lizzie]

In a lot of cultures it is taboo to start preparing for a baby (like making the babies room) during the first trimester, since the chance of a miscarriage is much higher then in the second and third trimester. In some cultures women don’t even tell people there are pregnant until their second trimester. I know a lot of women who practice this second trimester tradition.
But it would make sense to me to wait until your 5th month (in the second trimester anyways) to start to decorate, so you can coordinate colors with the baby's gender. : )