title: Epidemiology of pregnancies with unknown last menstrual period.
abstract: A group of women with unknown last menstrual period was studied representing 16% of a total of 22 404 pregnant women recorded using a common perinatal form. Unknown menstrual period is associated with high rates of low birth weight and with low socioeconomic and sociodemographic status. Such characteristics are also associated with a high rate of preterm deliveries. Thus any possible bias introduced in studies of prematurity by ignoring the group of women with unknown last menstrual period should be carefully checked.
mesh_terms: D000293:Adolescent; D000328:Adult; D001827:Body Height; D005260:Female; D006801:Humans; D007230:Infant, Low Birth Weight; D007231:Infant, Newborn; D008423:Maternal Age; D008572:Menarche; D008598:Menstruation; D010298:Parity; D011247:Pregnancy; D012959:Socioeconomic Factors