title: Problems of sample size and selection in analyses of pregnancy outcomes.
mesh_terms: D000328:Adult; D001034:Apgar Score; D001724:Birth Weight; D044383:Black People; D005260:Female; D006801:Humans; D008423:Maternal Age; D008875:Middle Aged; D011247:Pregnancy; D012107:Research Design / Q000592:standards*; D012907:Smoking