Because there were few women in the
obese class II and III
category, which covered a wide range of prepregnancy BMI values (ie, 35.0 — 55.4), the lack of a detectable effect of breastfeeding in the heaviest women may
result from inadequate statistical power rather than from a biological difference.
Also, because parents reported their own height and weight, some overweight and
obese parents may have been misclassified into a lower BMI
category, but it seems unlikely that this would have greatly altered
results.