Because our study was specifically designed to evaluate risks for low birth weight, we were limited in our ability to assess whether resin-based filling materials increase birth weight. Analysis limited to those women with an infant weighing 2,500 g or more could not identify an association between resin-based, tooth-filling materials and increased birth weight. Case-control studies specifically designed to detect macrosomia (>4,000 g) will be more sensitive to detect any potential association between plastic filling materials and increased birth weight.