title: Uterine length and fertility outcomes: a cohort study in the IVF population.
abstract: OBJECTIVE
  What is the relationship between pre-cycle uterine length and IVF outcome (chemical pregnancy, clinical pregnancy, spontaneous abortion and live birth)?
  
  
  CONCLUSIONS
  Women at extremes of uterine length (<7.0 or >9.0 cm) were less likely to achieve live birth and women with uterine lengths <6.0 cm were also more likely to experience spontaneous abortion.
  
  
  BACKGROUND
  A prospective study of 807 women published in 2000 found that implantation and clinical pregnancy rates were highest in women with uterine lengths between 7.0 and 9.0 cm, though the difference was not significant. The relationship between pre-cycle uterine length and live birth has not been evaluated.
  
  
  METHODS
  A retrospective cohort study of all cycles performed after uterine length measurement at an academic hospital IVF clinic from 2001 to 2012.
  
  
  METHODS
  A total of 8981 fresh cycles were performed in 5120 adult women with normal uterine anatomy. Women with uterine anomalies (unicornuate, bicornuate, septate or uterus exposed to diethylstilbestrol) were excluded and women with fibroids were identified for subanalysis. Uterine length was measured by uterine sounding. Cycles were divided by uterine length into groups: <6.0 cm (very short, n = 76), 6.0-6.9 cm (short, n = 2014), 7.0-7.9 cm (referent, n = 4984), 8.0-8.9 cm (long, n = 1664) and ≥9 cm (very long, n = 243). Multivariate logistic regression (first-cycle analyses) and generalized estimating equations (all-cycle analyses) were adjusted for age, fibroids and ART treatment (assisted hatching, intracytoplasmic sperm injection) to generate relative risk (RR) of cycle outcomes by uterine length.
  
  
  RESULTS
  Median uterine length in the IVF population was 7.0 cm (interquartile range 7.0-7.8) and was positively associated with BMI (P < 0.001) and fibroids (P = 0.02). Compared with the referent group, women with uterine lengths <6.0 cm were half as likely to achieve live birth (RR: 0.53; 95% confidence interval (CI): 0.35-0.81) and women with lengths of 6.0-6.9 cm were also less likely (RR: 0.91; CI: 0.85-0.98). Cubic regression spline identified a significant inverse U-shaped association whereby women with uterine lengths <7.0 or >9.0 cm were less likely to achieve live birth. Women with lengths <6.0 cm were also more likely to experience spontaneous abortion (RR: 2.16; CI: 1.23-3.78). Results remained consistent when excluding women with a uterine factor diagnosis (n = 8823), when limiting to the first cycle at our institution (n = 5120) and when further restricting to first-ever cycles (n = 3941).
  
  
  CONCLUSIONS
  Optimal assessment of uterine length by ultrasound was not feasible due to time and cost limitations, though uterine sounding is a clinically relevant measurement allowing for results with practical implications. Findings from our predominantly Caucasian clinic population may not be generalizable to infertile populations with different ethnic compositions.
  
  
  CONCLUSIONS
  Reproducibility of results would solidify findings and inform patient counseling in women undergoing IVF.
  
  
  BACKGROUND
  No funding was sought for this investigation. MD declares relationships with UpToDate (royalties) and WINFertlity (consultant).
authors.affiliation: Department of Obstetrics and Gynecology, Northwestern University, Chicago, IL, USA.
authors.forename: L K
authors.initials: LK
authors.lastname: Hawkins
authors.forename: K F
authors.initials: KF
authors.lastname: Correia
authors.forename: S S
authors.initials: SS
authors.lastname: Srouji
authors.forename: M D
authors.initials: MD
authors.lastname: Hornstein
authors.forename: S A
authors.initials: SA
authors.lastname: Missmer
mesh_terms: D000022:Abortion, Spontaneous / Q000000981:diagnostic imaging / Q000453:epidemiology; D000328:Adult; D015992:Body Mass Index; D005260:Female; D005298:Fertility; D005307:Fertilization in Vitro; D006801:Humans; D007889:Leiomyoma / Q000150:complications / Q000000981:diagnostic imaging; D015999:Multivariate Analysis; D009929:Organ Size; D011247:Pregnancy; D011256:Pregnancy Outcome; D012044:Regression Analysis; D012189:Retrospective Studies; D012307:Risk Factors; D014463:Ultrasonography; D014599:Uterus / Q000033:anatomy & histology* / Q000000981:diagnostic imaging / Q000502:physiology
keywords: IVF/ICSI outcome; cohort study; embryo transfer; infertility; uterus