title: Factors influencing twins and zygosity.
abstract: Zygosity is influenced by many factors. Monozygotic twins occur spontaneously in approximately 1 in 250 births and are felt to increase twofold with ovulation induction techniques. Monozygotic twinning also increases in proportion to the number of blastocysts transferred during in vitro fertilisation. In contrast, dizygotic twinning appears to be influenced by race, genetic factors, maternal age, fertility enhancing drugs, folic acid supplementation, and maternal nutritional status.
authors.affiliation: Department of Obstetrics and Gynecology, The University of Texas Medical Branch, Galveston, TX, USA. ghankins@utmb.edu
authors.forename: Gary V D
authors.initials: GV
authors.lastname: Hankins
authors.forename: George R
authors.initials: GR
authors.lastname: Saade
mesh_terms: D019587:Dietary Supplements; D005299:Fertility Agents / Q000627:therapeutic use; D005307:Fertilization in Vitro; D005492:Folic Acid / Q000008:administration & dosage; D006801:Humans; D008423:Maternal Age; D009752:Nutritional Status; D010062:Ovulation Induction; D014429:Twins, Dizygotic; D014430:Twins, Monozygotic
chemical_list: D005299:Fertility Agents; D005492:Folic Acid