Our first 3 are all 2 yrs apart, all boys. Ds1 was easy, easy going, easy training, easy nursing, easy sleeping. Ds2, was difficult nursing, never slept, walked late, talked late, got teeth late. Ds3, was a well....difficult in the sense, he was a klingon, but otherwise, pretty textbook. Then ds4 came, 4 yrs later, ds3 then became more independent, stopped screaming at prek drop off (he was 4), and he got LOUD, he is 10 and still the loudest child ever. Ds4, well he is my most difficult, he is just into everything, safety is furthest from his mind, however, he keeps us more than busy. I probably would have stopped at him, but.. we had ds5, I can tell you he is much like ds1, so refreshing.
Once you have 3 it does not matter how many kids you have. I always thought I would have a little girl, but it was not in our cards I guess. I feel good, the mini van is full, and now we can just cart these kids everywhere.
Your only 34, still young. I was 37 when I had ds5. Pregnancy wise, they were all pretty miserable in the beginning, morning sickness so bad, hospitalized a few times during pregnancy 2. Pregnancy 4 was difficult from start to finish, but I still would have done it.
Good luck with your decision.