“Does low birth weight correlate with growth?”

A weight of 5 pounds 1 oz at birth for a full-term baby (37-41 weeks) is small for gestational age. This weight could be in the normal range for a preterm infant (less than 37 weeks) depending on the gestation of the infant at birth. In other words, if the infant was a month or more early, this could be a normal weight. Assuming this infant is a term infant, there are many reasons for low birth weight including growth restriction from a poor functioning placenta (the organ that transfers nutrients from mom to baby). Other reasons include genetic reasons, mom's that smoke or use non-prescription medications, high blood pressure in pregnancy, and maternal diabetes. How a baby grows after birth and the first week of life (when most infants lose a little weight) depends on the cause of the low birth weight. Many infants born small, whatever the cause, can grow to their full potential which is estimated by their parental heights. The opposite is also true. Some large for gestational age infants (greater than the 90%) don't necessarily become large adults. The key to growth is good nutrition and a healthy, nurturing environment. So, if your sister is providing these important contributors to growth and well-being, the baby should grow well and to what we call the infant's genetic potential.
I hope this answers your question!