Gestational age-specific birthweight of twins in vital records.

Analysis of singleton preterm birth from vital statistics data is hampered by inaccurate gestational age dating. This is most notably evidence by the large fraction of implausibly high birthweights for gestational age given in birth records. Using natality statistics for New England, 1977-88, birthweight distributions were plotted for representative preterm gestations. Confounding by improbable birthweights was observed to be considerably less among preterm twin births than among preterm singleton births.