The number of children born by assisted reproductive technology (ART) is steadily rising. It is important to pursue the safety of ART and indispensable to survey perinatal outcome and follow-up babies. Recently, Pelkonen et al. reported that there was a statistical difference of the singleton birthweight after frozen-thawed embryo transfer (frozen-thawed ET) compared with fresh embryo transfer (fresh ET) in Finland (Hum Reprod, 2010). The aim of this study is to compare the perinatal outcomes of singleton born after frozen-thawed and fresh embryo transfers at a large IVF center in Japan.
【Materials and Methods】
2440 singletons born after ART treatments at our clinic from January 2005 to December 2009 were evaluated. In addition to ET procedures, we assessed several factors possibly affecting birthweight such as the age, height and weight of their parents and birth-height and gestational age of newborns. The questionnaires were mailed to 2430 cases; 10 cases were excluded first due to unknown address. 1202 cases replied, but 77 cases were excluded because of incomplete details. So finally 1125 cases were evaluated; 880 births after frozen-thawed ET and 245 births after fresh ET. As a reference of birthweight, the mean birthweight of overall Japanese newborns in 2009 was used.
【Results and Conclusions】
The mean birthweight in frozen-thawed ET and fresh ET singletons were 3062.3g and 2949.4g, respectively. The mean birth-height were 48.8cm and 48.2cm, respectively. Those of frozen-thawed ET singletons were significantly heavier and higher than those of fresh ET group (p<0.001). Statistical differences were not found with regard to age, height and weight of their parents and gestational ages. Compared with the mean birthweight of overall Japanese newborns, the frozen-thawed group was heavier and the fresh ET group was lighter.