It's really hard to say as all sizes are so very different. All bonds stuff are very small sizes. Unless you expect a very small bubs I would prob stick with most 000 & some 0000. I say better it big a bit bigger than not worn again after just a few weeks. Our DS was 6pds 12ozs & very long, because of long legs he went straight into 000, at almost 5months now he's 90% above average for length & because of this already in 0 suits for the past month or two.