Multiples do tend to be born smaller than single babies. But it’s not because their growth rate is necessarily slower — in fact, for twins, it’s about the same as any other baby’s until about weeks 30 to 32, when they do slow down a tad, since they’re competing more for nutrients. (Triplets slow earlier — around week 27 or 28.) The real reason multiples are more likely to have low birth weights is that they’re more likely to be born preterm (60 percent of twins and 90 percent of triplets are born before week 37).
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