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Updated: Oct 2, 2025
Human Blastocyst Biopsy and Vitrification
Published on: July 26, 2019
The effect of vitrified-warmed blastocyst transfer on postnatal growth: a 1-year follow-up questionnaire study
Alessandra Alteri1, Giovanni Campo2, Luca Pagliardini3
1Obstetrics and Gynaecology Unit, IRCCS San Raffaele Scientific Institute, Milan, Italy; Vita-Salute San Raffaele University, Milan, Italy.
Insights
Children born after frozen embryo transfer (FET) show increased height at 12 months. Males born after FET exhibit sex-specific growth differences, with slower weight gain during the first year compared to fresh embryo transfer.
Area of Science:
- Reproductive Medicine
- Pediatric Growth and Development
- In Vitro Fertilization
Background:
- Assisted reproductive technologies, including fresh and frozen embryo transfer (FET), are widely used for infertility treatment.
- Understanding the long-term growth outcomes of children born after these procedures is crucial for assessing their health and development.
Purpose of the Study:
- To compare the postnatal growth of singletons at 12 months of age born after vitrified-warmed blastocyst transfer (FET) versus fresh blastocyst transfer.
- To investigate potential sex-specific differences in growth trajectories following FET.
Main Methods:
- Retrospective cohort study at a single fertility center (2014-2016).
- Included women with singleton live births after fresh or FET at the blastocyst stage.
- Propensity score inverse probability weighting was used to balance baseline characteristics.
Main Results:
- FET singletons had significantly higher birth weight and length z-scores compared to fresh transfer.
- At 12 months, FET singletons showed significantly higher height z-scores but similar weight z-scores compared to fresh transfer.
- Males born after FET had higher birth weight z-scores but a slower weight growth trajectory during the first year.
Conclusions:
- Singleton infants born after FET exhibit increased height at 12 months compared to those born after fresh embryo transfer.
- Sex-dependent differences in growth trajectories are observed, particularly in weight gain for males born after FET.
Research Question:
Is postnatal growth of singletons aged 12 months born after vitrified-warmed blastocyst transfer (frozen embryo transfer [FET]) different from children born after fresh blastocyst transfer?
Design:
A retrospective cohort study conducted at a single university-affiliated obstetrics and fertility centre between 2014 and 2016. Women who underwent fresh transfer or FET at blastocyst stage and obtained a singleton live birth were included. Propensity score inverse probability weighting was used to balance baseline maternal characteristics between fresh and FET cycles.
Results:
Of the 382 women with singleton live births, 124 underwent a fresh blastocyst transfer and 258 underwent a FET. Significantly higher birth weight and length z-scores were observed after FET (P = 0.01 and P = 0.002, respectively) compared with the fresh transfer group. At 12 months of age, the fresh and FET groups showed no significant effect on the weight z-score, but the FET was associated with a higher height z-score (P = 0.001) compared with fresh blastocyst transfer. The comparison between males and females from the same study group showed higher birth weight z-score for males in the FET group (P < 0.001). During the first 12 months, however, males in the FET group showed a slower growth trajectory in terms of weight (P = 0.007).
Conclusions:
At 12 months of postnatal life, an increased height and sex-dependent differences in growth trajectories were observed in singletons born after FET compared with those born after fresh embryo transfer.
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