Fresh and Frozen-Thawed Embryo Transfer Compared to Natural Conception: Differences in Perinatal Outcome

Abstract

Background/Aim: To compare the pregnancy outcome of singletons conceived after transfer of cryopreserved and thawed embryos (frozen embryo transfer [FET]) to singletons conceived after fresh embryo transfer (fresh ET) and natural conceived singletons. Methods: Using a retrospective data analysis on a study population consisting of 1,261 singletons born after FET and 2,519 singletons born after fresh ET between 2006 and 2015. The control group consisted of singletons born after natural conception. Main outcome measures consisted of birth weight (in grams), gestational age, preterm birth (<37 weeks of gestation), being large for gestational age (LGA, above 90th weight percentile adjusted for gestational age) and Apgar scores. Results: Babies born after FET had an increased risk of high birth weight (adjusted OR [AOR]) 2.92; 1.503-3.482) and being LGA (AOR fresh ET vs. FET 1.47; 1.210-1.787) compared to singletons born after fresh ET, as well as higher birth weights compared to natural conceived children. Conclusions: Singletons born after FET have a higher risk of high birth weight and being LGA compared to singletons after fresh ET and compared to natural conceived singletons. We assume that the freezing process might be the underlying cause.

Large for gestational age and macrosomia in singletons born after frozen/thawed embryo transfer (FET) in assisted reproductive technology (ART)

“…Ten studies reported macrosomia outcomes in a total of 108.715 FET singletons. The risk of macrosomia in relation to FET was assessed in eight studies, of which six studies were included in meta‐analysis (Litzky et al, ; Maheshwari et al, ; Pinborg et al, ; Sazonova et al, ; Spijkers et al, ; Wennerholm et al, ). All of the studies included in meta‐analysis were cohort studies.…”

“…This should be considered when analyzing the increased risk of LGA in FET babies, as they normally have a higher birth order than children conceived after fresh embryo transfer. Yet, the difference in risk of LGA and macrosomia has persisted after adjustment for parity in several of the included studies (Li et al, ; Luke et al, ; Maheshwari et al, ; Marino et al, ; Pelkonen et al, ; Pinborg et al, ; Sazonova et al, ; Spijkers et al, ; Wennerholm et al, ).…”

“…The risk of LGA in relation to FET was assessed in 13 studies. Ten studies were eligible for inclusion in the meta-analysis (Ishihara et al, 2014;Kato et al, 2012;Li, Wang, Ledger, Edgar, & Sullivan, 2014;Luke et al, 2017;Marino et al, 2014;Pelkonen et al, 2010;Pinborg et al, 2014;Sazonova et al, 2012;Spijkers et al, 2017;Wennerholm et al, 2013). All the studies included in the meta-analysis were cohort studies.…”

“…However, a significantly higher adjusted mean birth weight of singletons after FET cycles has been reported over the last years (Feng et al, 2012;Henningsen et al, 2011;Kato et al, 2012;Maas, Galkina, Thornton, Penzias, & Sakkas, 2016;Nakashima et al, 2013;Ozgur, Berkkanoglu, Bulut, Humaidan, & Coetzee, 2015;Pelkonen et al, 2010;Roy, Bradley, Bowman, & McArthur, 2014;Shih et al, 2008;Spijkers, Lens, Schats, & Lambalk, 2017) and a tendency toward children being born large for gestational age (LGA) following FET has been established (Pelkonen et al, 2010;Pinborg et al, 2014;Sazonova, Kallen, Thurin-Kjellberg, Wennerholm, & Bergh, 2012).…”

Elective freeze-all embryos: What is the scientific evidence?

“…Spijker et al also showed the risk of high birth weight (>4,500g) and being large for gestational age was higher in the FTET group than in the FET group. 17 However, there were some studies reporting no difference of live birth weight between fetuses after FTET and FET. 18,19 Some results of studies related to the perinatal/obstetric outcome may be inconsistent, and they are mainly observational studies, thus it is considered that more randomized controlled studies are needed in the future.…”