1st year is most critical as this is the time baby's development & growth become established. It is common for baby to lose weight during the 1st week of life. For a larger baby, this may be as much as 1lb (450g), or for smaller babies, 6-8ozs (200g). After this, the average weight gain is about 1oz/day (28g). Average weight gain to be expected over the 1st year is:
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6mths - 2 x birth-weight
1yr - 3 x birth-weight
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Every baby is different, so variations should be expected. If your baby is 15% below/above expected weight, seek medical advice. Failure to gain weight may be due to feeding problems or problems of absorption.
Possible causes are:
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inadequate or poor quality breast milk
unsuitable type of {artificial milk}
wrong dilution of artificial milk
intolerance of baby to {lactose}
various rare malabsorption diseases
worm infestations
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Baby may have difficulty fixing to nipple due to:
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poorly developed nipples
{inverted nipples}
undershot jaw
poorly developed suck reflex, particularly premature babies
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Mother might not produce enough milk because of:
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poorly developed breasts
inadequate stimulation of breast tissue by {pituitary hormones}
inadequate stimulation because of poor sucking reflex