Frozen Embryo Replacement (FER) Has Better Outcomes Compared To Fresh In Vitro Fertilization (IVF)

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Frozen Embryo Replacement (FER) Has Better Outcomes Compared To Fresh In Vitro Fertilization (IVF)

Main Category: Fertility
Also Included In: Pregnancy / Obstetrics
Article Date: 13 Feb 2013

In a study to be presented on February 14 between 1:15 p.m., and 3:30 p.m. PST, at the Society for Maternal-Fetal Medicine's annual meeting, The Pregnancy Meeting™, in San Francisco, California, researchers will present findings showing perinatal outcomes of frozen/thawed embryo replacement (FER) have better outcomes compared to fresh in vitro fertilization (IVF), but worse outcomes compared to the non-IVF general population.

The study collected data from all IVF treatments in Denmark, Norway and Sweden from 1984 - 2007, then cross-linked with the Nordic Medical Birth Registries. Babies born after FER (6,653) were compared to those born after fresh IVF (42,287) and the general population (288,868). Researchers looked for eight different outcomes: low birth weight, very low birth weight, preterm birth, very preterm birth, small for gestational age, macrosomia (excessive birth weight), large for gestational age, and stillbirth.

"FER is used increasingly in IVF programs to avoid the risks associated with multiple births," said Ulla-Britt Wennerholm, of Sahlgrenska University Hospital in Göteberg, Sweden. "We sought to analyze the outcomes compared to spontaneous conceptions and fresh IVF."

Dr. Wennerholm and her associates found children born after FER had higher rates of PTB, very PTB, LBW, very LBW, LGA, and macrosomia compared to spontaneous conceptions. However, when compared to fresh IVF births, children born after FER fared better, having lower rates of PTB, LBW, and SGA. But they also found children born after FER to have higher rates of LGA and macrosomia than those born from fresh IVF.

Researchers concluded outcomes for FER to be better compared to fresh IVF, but worse compared to the general population. However, they believe the higher rates of LGA and macrosomia compared to fresh IVF will require further attention.

Abstract 30: Perinatal outcome in singletons born after replacement of frozen/thawed embryos

OBJECTIVE: Frozen/thawed embryo replacement (FER) is increasingly used in IVF programs. The option of freezing spare embryos supports the strategy of single embryo transfer, thereby reducing the wellknown risk of adverse outcomes related to multiple births. The aim of the present study was to analyse the perinatal outcome in a Nordic study on singletons born after FER in comparison with singletons born after fresh IVF cycles and singletons in the general population.

STUDY DESIGN: Data were collected for all IVF treatments in Denmark, Norway and Sweden during 1984-2007. Data were crosslinked with the Nordic Medical Birth Registries. Singletons born after FER were compared with singletons born after fresh IVF and singletons in the general population. Outcomes were low birth weight (LBW), very LBW, preterm birth (PTB), very PTB, small for gestational age (SGA), macrosomia (> 4500g), LGA and stillbirth. Crude and adjusted odds ratios with 95% CI were calculated. Adjustment was made for maternal age, parity, child sex and year of birth.

RESULTS: There were 6653 children born after FER, 42287 singletons born after fresh IVF and 288868 singletons born after non IVF. As compared with the general population singletons born after FER had higher rate of PTB (AOR 1.4; 1.2-1.5), very PTB (AOR 1.8; 1.5-2.3), LBW (AOR 1.3; 1.1-1.4), very LBW (AOR 1.71.3-2.2), LGA (AOR 1.3; 1.2-1.5) and macrosomia (AOR 1.4;1.2-1.5). As compared with fresh IVF, singletons born after FER had lower rate of PTB (AOR 0.9-1.0), LBW (AOR 0.8; 0.7-0.9) and SGA (AOR 0.8; 0.7-0.9) and higher rate of LGA (AOR 1.4; 1.2-1.6) and macrosomia (AOR 1.5; 1.3-1.7). For other outcomes no signiﬁcant differences were found.

CONCLUSION: This is the largest population based study on singletons born after FER. It conﬁrms previous studies of a worse perinatal outcome as compared with the general population and a better outcome as compared with fresh IVF. However, the increased rate of LGA and macrosomia needs further studies.

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