Blastocyst transfer is not associated with increased rates of monozygotic twins when controlling for embryo cohort quality

Fertil Steril. 2015 Jan;103(1):95-100. doi: 10.1016/j.fertnstert.2014.10.013. Epub 2014 Nov 5.


Objective: To compare monozygotic twinning (MZT) rates in patients undergoing blastocyst or cleavage-stage ET.

Design: Retrospective cohort.

Setting: Academic research center.

Patient(s): Autologous, fresh IVF cycles resulting in a clinical pregnancy from 1999 to 2014.

Intervention(s): None.

Main outcome measure(s): Monozygotic twin pregnancy in blastocyst-stage transfer vs. cleavage-stage transfer when controlling for patient prognosis and embryo cohort quality factors.

Result(s): There were a total of 9,969 fresh transfer cycles resulting in a pregnancy during the study period. Of these pregnancies, 234 monozygotic twin pregnancies were identified (2.4%). Of all transfers, 5,191 were cleavage-stage and 4,778 were blastocyst-stage transfers. There were a total of 99 MZT identified in the cleavage-stage group (1.9%) and 135 MZT in the blastocyst ET group (2.4%), which was significant. Multivariable logistic regression revealed that increasing age was associated with a significant reduction in MZT, regardless of transfer order. Embryo cohort quality factors, including the number and proportion of six- to eight-cell embryos and availability of supernumerary embryos, were also significant. When controlling for patient age, time period during which the cycle took place, the number and proportion of six- to eight-cell embryos, and availability of supernumerary embryos, there was no longer a difference in MZT rate between blastocyst and cleavage transfer.

Conclusion(s): Patient prognosis and embryo cohort quality seem to be major factors in MZT rate in women undergoing blastocyst transfer. Although technology-based effects cannot be excluded, patient and embryo characteristics play an important role.

Keywords: IVF; blastocyst; monozygotic pregnancy; twinning.

MeSH terms

  • Adult
  • Cohort Studies
  • Embryo Transfer / statistics & numerical data*
  • Female
  • Humans
  • Incidence
  • Infertility / epidemiology*
  • Infertility / therapy*
  • New Jersey / epidemiology
  • Pregnancy
  • Pregnancy Outcome / epidemiology*
  • Pregnancy, Twin / statistics & numerical data*
  • Retrospective Studies
  • Risk Factors
  • Treatment Outcome
  • Twins, Monozygotic / statistics & numerical data*