[QUOTE=LaffNowCryLater;14616860]
"Biliary atresia (my anatomy scan did not show this birth defect)"
I'm not sure if my comment is particularly helpful or relevant to the larger question being asked here but an anatomy scan done during pregnancy will not show any evidence of biliary atresia, the vast majority of the time. My son has biliary atresia

and all my prenatal scans showed no problems with his liver. The perinatal form of biliary atresia accounts for about 90% of biliary atresia cases. Symptoms typically don't become evident until 2-8 weeks of life - which is the same period of time that infants with Vitamin K deficiency are at high risk for a late VKDB (bleeds).
I believe the reason that breastfeeding is listed as a risk factor is because many babies with late VKDB have an underlying/undiagnosed liver disease. Due to the liver disease, they are unable to easily absorb vitamins, including Vitamin K (and fat). Since breastmilk is not high in Vitamin K, this can exacerbate the problem with the vitamin K deficiency in these particular babies and increases the risk of a late bleed. For healthy breastfed babies who do not have liver disease, this is not an issue.
So, what I'm trying to say is that you really won't know if your child has biliary atresia or a number of other liver diseases (like Alpha 1 or Alagille Syndrome) at birth and in the early weeks after. Some form of vitamin K supplementation during this time can help reduce your child's risk of a brain bleed if they happen to have one of these rare diseases. I'm not sure if this is really helpful to anyone making a decision about Vitamin K but I just wanted to mention our experience with liver disease.
Also, this is a link to an article on Vitamin K supplementation, breastfeeding, and liver disease - and it mentions some stuff about oral vitamin k doses:
igitur-archive.library.uu.nl/dissertations/2009-0414-200435/hasselt.pdf
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