Re: How long can I let LO sleep at night
Babies typically eat far more from a bottle than they do from the breast, because as you said, the flow is faster and the baby has little control over how much she consumes. A baby may take in 2-3 oz at the breast and maybe 1-2 oz more than that from a bottle. This is why babies tend to sleep longer and may seem more "content" after eating from the bottle. It's not really contentment, though: it's sleepiness from being stuffed full and having a huge meal to digest. A 1.5-2 hour spacing between nursing sessions is very normal. It's rare to find a young baby who routinely goes 3 hours between feedings, though older babies will often go that long, particularly after they start eating solid foods.
When a baby starts sleeping through the night, it is fine to allow her to do so provided she has normal diaper output and weight gain. Sleeping through the night after 6 weeks is unlikely to impact your milk supply that much, since your body has a very sensitive internal clock which allows it to make the right amount of milk for a given time of day. Frequent nursing during the day will train your body to produce plenty of milk while the sun is up, and when baby sleeps your milk production will throttle back overnight.
You are not required to feed at night in order to maintain a good supply, provided you nurse on demand both night and day. However, routinely going >6 hours without nursing often allows your prolactin (the milk-producing hormone) levels to drop low enough for long enough that your menstrual cycle will return. If a mom is relying on breastfeeding for contraception, she cannot do so once her baby starts sleeping through, because she'll end up pregnant and then her supply likely will diminish or vanish.
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