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Virtanen I, Polo-Kantola P, Erkkola R, Polo O, Ekholm E.Virtanen I, et al.Br J Obstet Gynaecol. 1999 Feb;106(2):155-64. doi: 10.1111/j.1471-0528.1999.tb08216.x.Br J Obstet Gynaecol. 1999.PMID: 10426682Clinical Trial.