title: Preterm delivery risk factors in singletons born after in vitro fertilization procedures.
abstract: OBJECTIVE
  Women delivering singletons after in vitro fertilization (IVF) procedures have a greater risk of preterm delivery (PD). The aim of our study was to analyze PD risk factors and to identify those that could possibly be prevented.
  
  
  METHODS
  In our matched controlled study we analyzed 1127 singleton deliveries after IVF and transfer of fresh embryos performed at the University Medical Center Ljubljana between 1 January 2002 and 31 December 2010. For every delivery included in the study group we chose three consecutive controls matched by maternal age, parity and maternity hospital. The main outcome measure was PD (<37 weeks). Investigated variables were: previous PD (PPD), conization, pregestational diabetes mellitus, uterine anomaly, operation on the uterus, chronic renal disease, maternal age and parity, and body mass index (BMI). Variables investigated within the IVF group were: stimulation protocol, laboratory procedure, number of retrieved oocytes and number and quality of transferred embryos.
  
  
  RESULTS
  The PD rate after IVF was 1.5 times higher than after natural conception (11.5% in the IVF group and 7.7% in the control group, p<0.001). Conization and chronic renal disease were shown to be significant risk factors for PD in both the IVF group and the naturally conceiving controls. BMI>30 was an important risk factor only in the IVF group (OR 1.86 (1.06-3.27) vs. 1.10 (0.67-1.80)) and PPD only in the controls (OR 1.83 (0.78-4.28) vs. 3.22 (1.55-6.67)). Among the investigated PD risk factors, an IVF procedure was shown to be the fifth most important one. On analyzing parameters of the ovarian stimulation and IVF procedure, no PD risk factor was identified.
  
  
  CONCLUSIONS
  IVF was shown to be a significant risk factor for PD. In the IVF population, BMI plays a far more important role in PD than in the fertile population. In our research PD reoccurrence in IVF group was less than expected, which could perhaps be explained by the surgical correction of gynecological pathology and, where necessary, its being combined with cerclage. The investigation of parameters related to the IVF procedure did not identify any risk factors for PD.
authors.affiliation: University Medical Center Ljubljana, Slajmerjeva 3, 1000 Ljubljana, Slovenia. Electronic address: helena.ban.frangez@gmail.com.
authors.forename: Helena
authors.initials: H
authors.lastname: Ban Frangez
authors.affiliation: University Medical Center Ljubljana, Slajmerjeva 3, 1000 Ljubljana, Slovenia.
authors.forename: Sara
authors.initials: S
authors.lastname: Korosec
authors.affiliation: University Medical Center Ljubljana, Slajmerjeva 3, 1000 Ljubljana, Slovenia.
authors.forename: Ivan
authors.initials: I
authors.lastname: Verdenik
authors.affiliation: University Medical Center Ljubljana, Slajmerjeva 3, 1000 Ljubljana, Slovenia.
authors.forename: Vanja
authors.initials: V
authors.lastname: Kotar
authors.affiliation: University Medical Center Ljubljana, Slajmerjeva 3, 1000 Ljubljana, Slovenia.
authors.forename: Urska
authors.initials: U
authors.lastname: Kladnik
authors.affiliation: University Medical Center Ljubljana, Slajmerjeva 3, 1000 Ljubljana, Slovenia.
authors.forename: Eda
authors.initials: E
authors.lastname: Vrtacnik Bokal
mesh_terms: D000328:Adult; D015992:Body Mass Index; D019092:Conization / Q000009:adverse effects; D005260:Female; D005307:Fertilization in Vitro; D006801:Humans; D007231:Infant, Newborn; D011247:Pregnancy; D011256:Pregnancy Outcome; D047928:Premature Birth / Q000453:epidemiology* / Q000209:etiology; D012307:Risk Factors; D017524:Slovenia / Q000453:epidemiology; D014599:Uterus / Q000002:abnormalities / Q000601:surgery
keywords: BMI; IVF; Preterm delivery; Risk factors; Singletons