title: Difference in birth weight of consecutive sibling singletons is not found in oocyte donation when comparing fresh versus frozen embryo replacements.
abstract: OBJECTIVE
  First, to assess if there are any differences in birth weight or gestational length in newborns from egg-donation pregnancies delivering singletons, originating from either fresh or frozen-thawed embryos when they were developed and delivered within the same mothers. Second, to determine if there are any clinical, phenotypic, or laboratory factors influencing this relationship, including the origin of the oocyte (same or different donor), the order of the children (first fresh or first frozen-thawed embryo transfer), the embryo freezing technique (vitrification or slow freezing), the in vitro embryo culture length, and the duration that embryos remained frozen.
  
  
  METHODS
  Retrospective cohorts study.
  
  
  METHODS
  University-affiliated infertility centers.
  
  
  METHODS
  A total of 360 women undergoing oocyte donation (OD), delivering (>28 weeks) at least two babies, each one from a single pregnancy, originating from at least one fresh and one frozen-thawed embryo transfer, controlling maternal and laboratory characteristics, to test the effect of embryo freezing on children size (n = 731).
  
  
  METHODS
  None.
  
  
  METHODS
  Birth weight, gestational age, weight percentile, being large for gestational age (LGA), small for gestational age (SGA), size out of normal range (ONR = LGA + SGA), and macrosomy.
  
  
  RESULTS
  From fresh versus thawed embryos, respectively, mean birth weight of children was 3,183.7 g versus 3,226.4 g, gestational age was 272.1 days versus 268.8 days, and mean weight percentiles were 47.6 versus 50.1. The proportions and corresponding odds ratios (ORs) from fresh versus thawed embryos, respectively, were for LGA 13.6% versus 11.3% (OR 0.81), for SGA 9.4% versus 12.5% (OR 1.37), for ONR 23.1% versus 23.8% (OR 1.04), and for macrosomy 0.3% versus 0.8% (OR 3.1). After adjusting for clinically relevant variables, the ORs were for LGA 0.96, for SGA 1.40, for ONR 1.20, and for macrosomy not computable. None of the stated measures were significantly different. Also, independent analyses run on the origin of the oocytes, cryopreservation technique, cleavage stage of the embryos, and time that embryos remained frozen did not reveal any significant trends.
  
  
  CONCLUSIONS
  This study comparing siblings from OD cycles, and eliminating the independent variables that affect early events in pregnancy, revealed no difference in duration of gestation and live birth weights between fetuses obtained after the replacement of fresh or frozen embryos. Moreover, no clinical, phenotypic, or laboratory factors appeared to be relevant, once statistically controlled.
authors.affiliation: Reproductive Medicine Unit, IVI Barcelona, Barcelona, Spain; IVI Roma, Rome, Italy; IVI Foundation, Valencia, Spain. Electronic address: daniela.galliano@ivi.es.
authors.forename: Daniela
authors.initials: D
authors.lastname: Galliano
authors.affiliation: IVI Foundation, Valencia, Spain; Andrology Laboratory and Semen Bank, IVI Valencia, Valencia, Spain.
authors.forename: Nicolás
authors.initials: N
authors.lastname: Garrido
authors.affiliation: Feto-Maternal Medicine Unit, IVI Valencia, Valencia, Spain.
authors.forename: Vicente
authors.initials: V
authors.lastname: Serra-Serra
authors.affiliation: Reproductive Medicine Unit, IVI Valencia, Valencia, Spain; Department of Obstetrics and Gynecology, Hospital Politécnico y Universitario La Fe, Valencia, Spain.
authors.forename: Antonio
authors.initials: A
authors.lastname: Pellicer
mesh_terms: D001724:Birth Weight; D016009:Chi-Square Distribution; D015925:Cryopreservation; D004624:Embryo Transfer / Q000009:adverse effects; D005260:Female; D005298:Fertility; D005307:Fertilization in Vitro / Q000009:adverse effects; D005865:Gestational Age; D006801:Humans; D007246:Infertility / Q000175:diagnosis / Q000503:physiopathology / Q000628:therapy*; D050498:Live Birth; D016015:Logistic Models; D008297:Male; D016017:Odds Ratio; D018587:Oocyte Donation / Q000009:adverse effects; D011247:Pregnancy; D012189:Retrospective Studies; D012307:Risk Factors; D035781:Siblings; D016896:Treatment Outcome
keywords: Birth weight; frozen embryo transfer; large for gestational age; macrosomia; oocyte donation; small for gestational age