Do you know how low they got weight wise with the normal initial weight loss? You would calculate their gain from there.... so really it depends on how much they've gained from their lowest weight.  I know that my pedi wanted to see more like an oz/day in the early days.  Their weight gain slowed to about 4-5oz/week around week 8 or so. They still at 4 1/2 months gain 4-5oz/week....
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Really at 9 weeks old the minimum gain should be about32 ounces... (4oz/week for 8 weeks as the first week they were probably loosing)  but that is from the lowest weight they had. Â
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I also agree that the infrequent pooping may be a concern... it's hard to say for sure... but 3 weeks is a LONG time, esp at such a young age. I read that for the first six weeks they should be going a few times/day. I know my girls did. Now it is normal for EBF babies to slow down their pooping but 3 weeks seems too long.Â
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I agree about what PP said... if you can't find an IBCLC is there a La Leche Leader around that can help evaluate nursing?  I also agree with somehow finding a scale to measure their input. Of course it can vary feed to feed but the general rule is that babies need 24 oz of breastmilk/24 hours.  So if they nursed at 9 and then at 12 they should take in 3 oz a piece.  (of course time of day can vary, baby's appetite, etc)
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I do know that at that age I couldnt really do ANYTHING but nurse nonstop. I felt like all I did was sit on the couch nursing them.... so even them nursing every hour is not concerning.Â
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If it got to the point of needing supplementing (which I hope it doesnt!!!!) maybe consider donor milk over goat milk? The first week I used another mama's milk due to jaundice issues with one of my babes.  I was so glad to use the perfect nutrition for her.... if your babies were older (9 months plus) maybe goat's milk would be a good option, but they are quite young for that....