Is too rapid weight gain in an infant risky? My granddaughter weighed 7.7 pounds at birth and had doubled her weight by two months, and now, at three months has gained much more. She isn t due to be weighed until her 4-month doctor s visit, but she is very chubby, with a triple chin. She is entirely breast-fed and neither parent is overweight at all. Is she overweight, and is that risky? I worry about sleep apnea and SIDS risk.