title: Origin of multiple pregnancies in a subfertile population.
abstract: OBJECTIVE
  To evaluate the contribution of different subfertility treatments to the number of multiple pregnancies in a subfertile population.
  
  
  METHODS
  A prospective cohort study between January 2002 and December 2006.
  
  
  METHODS
  A subfertility clinic in a large regional training hospital in the Netherlands.
  
  
  METHODS
  A total of 1,001 continuing pregnancies, of which 63 (6.3%) were multiple.
  
  
  METHODS
  Of all pregnancies, mode of conception, outcome and type of pregnancy (singleton or multiple) were documented.
  
  
  METHODS
  Proportions of continuing and multiple pregnancies caused by the different modes of conception.
  
  
  RESULTS
  Of all subfertility related continuing pregnancies, 46% were conceived spontaneously, 16% were induced by clomiphene citrate (CC), 2.4% by follicle stimulating hormone (FSH) and 14% by intra-uterine insemination combined with controlled hyperstimulation (IUI/(COH)). In vitro fertilization (IVF) and its related techniques resulted in about a fifth of all continuing pregnancies (n = 212), but were responsible for more than half (n = 36) of the multiple pregnancies. Furthermore, 18% of the multiple pregnancies were induced by IUI/(COH), 3% by FSH, 11% by CC, whereas about 11% were conceived spontaneously.
  
  
  CONCLUSIONS
  IVF and intra-cytoplasmic sperm injection (ICSI) were responsible for the majority of the multiple pregnancies in a subfertile population. Therefore, twin prevention should be focused on further promoting elective single embryo transfer (eSET). Fertility treatment and particular IVF should not be started as long as the spontaneous pregnancy prognosis is good.
authors.affiliation: Department of Obstetrics and Gynecology, Jeroen Bosch Hospital, 's-Hertogenbosch, The Netherlands. m.brandes@jbz.nl
authors.forename: Monique
authors.initials: M
authors.lastname: Brandes
authors.forename: Carl J C M
authors.initials: CJ
authors.lastname: Hamilton
authors.forename: Kim A Y J
authors.initials: KA
authors.lastname: Bergevoet
authors.forename: Jan Peter
authors.initials: JP
authors.lastname: de Bruin
authors.forename: Willianne L D M
authors.initials: WL
authors.lastname: Nelen
authors.forename: Jan A M
authors.initials: JA
authors.lastname: Kremer
mesh_terms: D000293:Adolescent; D000328:Adult; D002996:Clomiphene / Q000627:therapeutic use; D005260:Female; D005300:Fertility Agents, Female / Q000627:therapeutic use; D005640:Follicle Stimulating Hormone / Q000627:therapeutic use; D006728:Hormones / Q000627:therapeutic use; D006801:Humans; D008137:Longitudinal Studies; D009426:Netherlands; D011247:Pregnancy; D011272:Pregnancy, Multiple; D011446:Prospective Studies; D027724:Reproductive Techniques, Assisted / Q000706:statistics & numerical data*; D055815:Young Adult
chemical_list: D005300:Fertility Agents, Female; D006728:Hormones; D002996:Clomiphene; D005640:Follicle Stimulating Hormone