Obstetric and Perinatal outcomes in singleton pregnancies resulting from the transfer of frozen thawed versus fresh embryos generated through in-vitro fertilization treatment A systematic review and meta-analysis

Pregnancies arising from the transfer of frozen thawed IVF embryos have better obstetric and perinatal outcomes based on the observational data.

Abha Maheshwari, M.D., Shilpi Pandey, M.R.C.O.G., Ashalatha Shetty, M.D., Mark Hamilton, M.D., Siladitya Bhattacharya, M.D.

Volume 98, Issue 2 , Pages 368-377.e9, August 2012


To perform a systematic review and meta-analysis of obstetric and perinatal complications in singleton pregnancies after the transfer of frozen thawed and fresh embryos generated through IVF.

Systematic review.

Observational studies, comparing obstetric and perinatal outcomes in singleton pregnancies subsequent to frozen thawed ET versus fresh embryo transfer, were included from Medline, EMBASE, Cochrane Central Register of Clinical Trials, DARE, and CINAHL (1984–2012).

Women undergoing IVF/intracytoplasmic sperm injection (ICSI).

Two independent reviewers extracted data and assessed the methodological quality of the relevant studies using critical appraisal skills program scoring. Risk ratios and risk differences were calculated in Rev Man 5.1. Subgroup analysis was performed on matched cohort studies.

Main Outcome Measure(s):
Antepartum hemorrhage, very preterm birth, preterm birth, small for gestational age, low birth weight, very low birth weight, cesarean section, congenital anomalies, perinatal mortality, and admission to neonatal intensive care unit.

Eleven studies met the inclusion criteria. Singleton pregnancies after the transfer of frozen thawed embryos were associated with better perinatal outcomes compared with those after fresh IVF embryos. The relative risks (RR) and 95% confidence intervals (CI) of antepartum hemorrhage (RR = 0.67, 95% CI 0.55–0.81), preterm birth (RR = 0.84, 95% CI 0.78–0.90), small for gestational age (RR = 0.45, 95% CI 0.30–0.66), low birth weight (RR = 0.69, 95% CI 0.62–0.76), and perinatal mortality (RR = 0.68, 95% CI 0.48–0.96) were lower in women who received frozen embryos.

Although fresh ET is the norm in IVF, results of this systematic review of observational studies suggest that pregnancies arising from the transfer of frozen thawed IVF embryos seem to have better obstetric and perinatal outcomes.

  • steven f palter

    great metaanalysis cryo embryo can be better?

  • Lauren Roth

    Oops, posted too early. It could signal a large change in future practice in our field. It is clear that future studies need to have uniform cryopreservation techniques and uniform techniques for frozen embryo transfer (supported by exogenous E and P or natural cycle).

  • Lauren Roth

    This is interesting data that could signal a large futue

  • Micah Hill

    This meta-analysis was well done with transparent methods. The potential mechanisms for poorer obstetrical outcomes in fresh cycles, such as an altered endometrial environment, are interesting. As with any meta-analysis, the main weakness is often the quality of the primary studies themselves, which in this case are all observational. As the authors state, their data supports a RCT to further investigate this issue.

  • Sergio Gonçalves

    Despite the possible confounders, which are clearly discussed, the idea of a more physiological environment in frozen-thawed cycles seems quite plausible.

  • Alfredo

    Good job! The authors provide a useful synthesis of the literature. They expose clearly the limitations of such a review and support their results with biological hypotheses. I’d be missing an influence analysis or a better understanding of the high heterogeneity in preterm delivery. I’d like to know why the authors chose to use raw instead of aggregate adjusted data, given that in observational studies confounders are usually controlled in the statistical analysis.

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