title: Increased risk of preterm birth and low birthweight with very high number of oocytes following IVF: an analysis of 65 868 singleton live birth outcomes.
abstract: OBJECTIVE
  Is there a relation between the number of oocytes retrieved following ovarian stimulation and obstetric outcomes of preterm birth (PTB) and low birthweight (LBW) following IVF treatment?
  
  
  CONCLUSIONS
  There is an increased risk of PTB (<37 weeks gestation) and LBW (<2500 g) following IVF in women with a high number (>20) of oocytes retrieved.
  
  
  BACKGROUND
  Pregnancies resulting from assisted reproductive treatments (ART) are associated with a higher risk of pregnancy complications compared with spontaneously conceived pregnancies. Whether ovarian ageing in women with poor ovarian response is associated with an increased risk of adverse obstetric outcomes is debated. It is also unclear if an excessive response and high egg numbers following ovarian stimulation have an association with adverse obstetric outcomes.
  
  
  METHODS
  Observational study using anonymized data on all IVF cycles performed in the UK from August 1991 to June 2008. Data from 402 185 IVF cycles and 65 868 singleton live birth outcomes were analysed.
  
  
  METHODS
  Data on all women undergoing a stimulated fresh IVF cycle with at least one oocyte retrieved between 1991 and June 2008 were analysed for birth outcomes. Logistic regression analysis of the association between ovarian response (quantified as number of oocytes retrieved) and outcomes of PTB and LBW was performed.
  
  
  RESULTS
  There was a significantly higher risk of adverse obstetric outcomes of PTB and LBW among women with an excessive response (>20 oocytes) compared with women with a normal response (10-15 oocytes): adjusted odds ratio (OR) 1.15, 95% confidence interval (CI) 1.03-1.28 for PTB, adjusted OR 1.17, 95% CI 1.05-1.30 for LBW, respectively. There was no increased risk of the adverse outcomes among women with a poor ovarian response (≤3 oocytes) compared with women with a normal response: adjusted OR 0.88, 95% CI 0.76-1.01 for PTB, adjusted OR 0.92, 95% CI 0.79-1.06 for LBW, respectively.
  
  
  CONCLUSIONS
  Although the analysis was adjusted for a number of potential confounders, the dataset had no information on other important confounders such as smoking, BMI and the medical history of women during pregnancy. Furthermore, the dataset did not allow specific identification of women with PCOS and its anonymized nature did not make it permissible to analyse one cycle per woman.
  
  
  CONCLUSIONS
  Analysis of this large dataset suggests that a high oocyte number (>20) following IVF is associated with a higher risk of PTB and LBW. These findings lead to speculation whether ovarian dysfunction and/or an altered endometrial milieu resulting from supraphysiological steroid levels underlie the unfavourable outcomes and warrant further research. Ovarian stimulation regimens should optimize the number of oocytes retrieved to avoid the risk of adverse outcomes associated with very high numbers of oocytes.
  
  
  BACKGROUND
  No funding was obtained. There are no competing interests to declare.
authors.affiliation: Aberdeen Fertility Centre, Aberdeen Maternity Hospital, Aberdeen, UK sksunkara@hotmail.com.
authors.forename: Sesh Kamal
authors.initials: SK
authors.lastname: Sunkara
authors.affiliation: Mother-Infant Department, Institute of Obstetrics and Gynaecology, University of Modena and Reggio Emilia, Modena, Italy.
authors.forename: Antonio
authors.initials: A
authors.lastname: La Marca
authors.affiliation: King's College London, London, UK.
authors.forename: Paul T
authors.initials: PT
authors.lastname: Seed
authors.affiliation: King's College London, London, UK.
authors.forename: Yacoub
authors.initials: Y
authors.lastname: Khalaf
mesh_terms: D000328:Adult; D016001:Confidence Intervals; D005260:Female; D005307:Fertilization in Vitro; D006801:Humans; D007230:Infant, Low Birth Weight; D050498:Live Birth; D016017:Odds Ratio; D054315:Oocyte Retrieval; D010062:Ovulation Induction / Q000009:adverse effects*; D011247:Pregnancy; D011256:Pregnancy Outcome; D047928:Premature Birth / Q000453:epidemiology*; D012307:Risk Factors
keywords: IVF; low birthweight; oocytes retrieved; preterm birth