title: Independent factors influencing large-for-gestation birth weight in singletons born after in vitro fertilization.
abstract: OBJECTIVE
  Higher risk for birth of singletons being large for gestational age (LGA) has been revealed after in vitro fertilization (IVF) frozen-thawed embryo-transfer (FET). This phenomenon is now being investigated, since there is a speculation that these neonates could suffer from underlying epigenetic disturbances. The aim of the study was to expose independent LGA risk factors and to identify those connected to the IVF techniques.
  
  
  METHODS
  Altogether, 4508 singleton pregnancies and births were included in the cohort case-matched study. Two hundred eleven singleton pregnancies and births after FET and 916 after fresh embryo transfer (ET) were included into two study groups. The IVF procedures were performed at the University Medical Centre Ljubljana between 2004 and 2011. For each IVF pregnancy, three matched consecutive controls after natural conception were included. Using logistic regression models, we observed LGA connection to maternal parameters (smoking, hypertension, parity, BMI, gestational diabetes, IVF conception, FET, double ET, and ICSI procedure).
  
  
  RESULTS
  Singletons born after FET had a significantly higher risk for being LGA (p = 0.032; OR 1.697; 95 % CI 1.047-2.752). BMI 25-30 was a significant independent risk factor for LGA in the IVF groups (FET p = 0.041, OR 2.460, 95 % CI 1.030-5.857 and fresh ET p = 0.003; OR 2.188, 95 % CI 1.297-3.691). ICSI and double ET had no significant effect on LGA occurrence.
  
  
  CONCLUSIONS
  Besides maternal BMI, FET is a significant independent LGA risk factor in IVF patients. Other observed factors (smoking, hypertension, multiparity, GDM, ICSI procedure, or number of embryos transferred) do not influence LGA risk significantly.
authors.affiliation: Department of Human Reproduction, Division of Gynaecology, University Medical Centre Ljubljana, Šlajmerjeva 3, 1000, Ljubljana, Slovenia. sara_korosec@hotmail.com.
authors.forename: Sara
authors.initials: S
authors.lastname: Korosec
authors.affiliation: Department of Human Reproduction, Division of Gynaecology, University Medical Centre Ljubljana, Šlajmerjeva 3, 1000, Ljubljana, Slovenia.
authors.forename: Helena Ban
authors.initials: HB
authors.lastname: Frangez
authors.affiliation: Department Perinatology, Division of Gynaecology, University Medical Centre Ljubljana, Šlajmerjeva 3, 1000, Ljubljana, Slovenia.
authors.forename: Lili
authors.initials: L
authors.lastname: Steblovnik
authors.affiliation: Research Unit, Division of Gynaecology, University Medical Centre Ljubljana, Šlajmerjeva 3, 1000, Ljubljana, Slovenia.
authors.forename: Ivan
authors.initials: I
authors.lastname: Verdenik
authors.affiliation: Department of Human Reproduction, Division of Gynaecology, University Medical Centre Ljubljana, Šlajmerjeva 3, 1000, Ljubljana, Slovenia.
authors.forename: Eda Vrtacnik
authors.initials: EV
authors.lastname: Bokal
mesh_terms: D000328:Adult; D001724:Birth Weight; D015992:Body Mass Index; D015331:Cohort Studies; D015925:Cryopreservation; D004624:Embryo Transfer / Q000009:adverse effects / Q000379:methods*; D005260:Female; D005307:Fertilization in Vitro; D005865:Gestational Age; D006801:Humans; D007231:Infant, Newborn; D011247:Pregnancy; D011256:Pregnancy Outcome; D012307:Risk Factors
keywords: Birth weight; Frozen–thawed embryo transfer; IVF outcome; IVF singletons; Large for gestation