Optimizing the temperature of embryo culture in IVF: a randomized controlled trial


      Significant animal data exist to indicate that the temperature in the mammalian reproductive tract is more than one degree cooler than core. Traditional IVF systems culture embryos at 37 C to mirror standard cell culture practice. No study to date has evaluated the relationship between different culture temperatures, embryo development, aneuploidy, and ultimately implantation and delivery rates. This study seeks to compare these outcomes following in vitro culture at 36 and 37 C.


      Paired Randomized Controlled Trial.

      Materials and Methods

      To assure optimal comparisons a paired study design was employed so that each patient served as her own control. The mature oocytes from one retrieved cohort were divided into two groups and one group was randomly assigned to culture at 36 C and the other to 37 C from the time of insemination until the time of transfer or cryopreservation. All patients were < 42 years old and had 8 or more mature oocytes. All were planned for 2 ET – 1 from each of the two groups. Paired statistical analyses of fertilization rate (FR), cleavage rate (CR), blastulation rate (BR), blastocyst morphologic grades (BM), aneuploidy rate (AR), and sustained implantation rate (SIR) were performed.


      Fifty one patients participated. Six had no euploid embryos from either group and did not undergo ET. Forty five patients underwent ET of 86 embryos. Embryologic development as evidenced by FR, CR, BR, and BM were equivalent for the two groups. Similarly, the 36 C and 37 C groups had equivalent SIR (75.8% versus 73.0, p=0.79), and AR (20.0% versus 23.8%, p=0.52).


      This paired RCT demonstrates that embryo culture at the more physiological temperature of 36 C has no detectable advantage over the more traditional culture system temperature of 37 C as evidenced by temporal and morphologic embryo development and AR. It also has no impact on developmental competence as evidenced by SIR. Further studies into more subtle aspects of embryo development such as methylation remain to be done.