29 weeks and beginning to worry about my marriage

I've been married to my husband for 6 years this year, we had a rocky 1st year.. All the changes of moving in together and just joining lives, but since then it has been wonderful and I honestly cannot bear the thought of our relationship changing. But with my due date closing in, I'm so scared of our marriage falling short and google is not helping!! I am a firm believer that marriage always comes first, before your children. I know I'm going to make the best effort to create a smooth transition for our new family of 3 but any tips would be greatly appreciated! Thanks!