I realise it's derailing the thread somewhat, and I don't want to do that but I do feel it's necessary to pick up on an error of fact which has been stated above.
tiktok, you said:
"Why all this about dehydration? The risk is not 'substantial'. Even severe neonatal hypernatraemic dehydration does not have sequelae (per the Oddie et al study which followed every case in the UK over a period of years) when treated. "
This is not correct ("does not have sequelae"). Oddie study, fn.bmj.com/content/98/5/F384.long did not do long term follow up. The only data was collected by having the managing paediatricians fill out a report card on the in-hospital stay, and they analysed the data on those in-hospital outcomes - showing babies were by and large fine when discharged. That does not mean they did not go on to have long term problems. We don't know that without specifically constructing a cohort of such babies and following them, with specific procedures for checking on particular aspects of their long term development.
As the authors say in their abstract "Aims: To describe incidence, presentation, treatment and short term outcomes"
I am not aware of any studies which do attempt to gather longer term data on the outcomes following hypernatremia, or substantial weight loss. In the absence of such data, we cannot make firm statements about the absence of harm. To be clear, substantial weight loss without hypernatremia, is likely to be much more common than hypernatremia (which corresponds to the most severe end of the spectrum of problems with milk intake).
If you know of studies which do report on such outcomes, please provide them, and we can all learn from the evidence.
In addition, the cutoff for hypernatremia in the Oddie study was 160 mmol/l, higher than conventional 150, which therefore indicates they would have captured a smaller group of babies with their more selective definition. There are other reasons to think the population prevalence estimate might be an under-estimate, but I won't go into these here as I do think overall it's a very valuable study, but shouldn't be read as gospel, just a starting point for further understanding of this important problem.
As an illustration that our knowledge of newborn feeding issues is evolving all the time, another study has suggested (absolutely not definitive, due to the possible biases) that long term problems might be associated with transient hypoglycemia:
www.ncbi.nlm.nih.gov/pubmed/26301959
In the light of this, we can't really assume that something as severe as hypernatremia in the 1st few weeks of life is completely harmless either.
I personally feel that I don't agree with some of your other points tiktok, but won't belabour them here so as to derail any further (and won't comment further on the discussion as I feel it's getting away from the OP's concerns) - but would just say, that there are very few areas of healthcare where we can happily say: "we know everything we need to know to operate safely and effectively, if only we were allowed to 100% apply our current knowledge". There are always uncertainties, and our understanding of lactation physiology, and BF, is actually not that great as compared to many other biomedical subjects. I would love to see a lot more research into the practical and clinical aspects of BF management eg, acknowledging the difficulties many mothers have in establishing BF (not just saying "low supply doesn't really exist, it's just all in your head or the fault of hospital practices), and trying to work out how to improve this. Which would involve to start with the folks who work in BF support acknowledging and engaging with researchers and clinicians on the studies that need to be done to fill in knowledge gaps. For example you imply with weighing data and nappy data we can confidently identify babies at risk of poor milk intake - nappy data are actually not that diagnostic; the diagnostic stats for nappy counts are not adequate for determining confidently that a baby is "fine" and not at risk from poor milk intake. I have heard it said too many times from those in BF support that substantial weight losses are not to be worried about - weight measurements can be "wrong" etc, so the baby is "fine". As Neifert said - "The fear that saying anything negative about breastfeeding will have an adverse effect on promotion efforts contributes to a conspiracy of silence about breastfeeding failures that impedes an understanding of the problem."
Pediatric practitioners are obligated to confront the reality of breastfeeding failure, identify associated risk factors, and implement intervention strategies to prevent infant morbidity."
And I will be off this thread now, apologies to the OP. I really hope you are happily making your decisions about how to manage your baby's feeding and getting all the support you need in real life. I am really sorry to hear that BF has been very hard work for you, but I hope now you will be able to either find it easier, if you decide to continue, or that stopping (if that is your decision) will enable you to get on with enjoying the interactions with your baby in other ways. So many things can have impacted on your baby's health, that it is really impossible to know, as folks say, what precisely the contribution of BF was versus other things. I am sure though, that the antibodies and other immune factors, will have been very valuable, and potentially will have helped her to be healthier than she otherwise would have been had she not had the BM. Whether you decide it was worth the work, is your decision only, and you don't need to share it with anyone. My best to you. xx