Should extended blastocyst culture include Day 7?

Abstract

Extended culture to the blastocyst stage is widely practised, improving embryo selection and promoting single embryo transfer. Selection of useable blastocysts typically occurs on Days 5 and 6 of embryo culture. Embryos not suitable for transfer, biopsy or cryopreservation after Day 6 are routinely discarded. Some embryos develop at a slower rate, however, forming blastocysts on Day 7 of culture. Day 7 blastocysts can be viable, they can be of top morphological grade, euploid and result in a healthy live birth. Since ending culture on Day 6 is current practice in most clinics, viable Day 7 blastocysts may be prematurely discarded. Although Day 7 blastocysts make up only 5% of useable blastocysts, those which are suitable for cryopreservation or biopsy are clinically significant. Overall, culturing embryos an additional day increases the number of useable embryos per IVF cycle and provides further opportunity for pregnancy for patients, especially those who have only a few or low-quality blastocysts.

Is day 7 culture necessary for in vitro fertilization of cryopreserved/warmed human oocytes?

“…Days 5, 6 and 7 blastocysts were 34.3, 50.0 and 15.6%, respectively. The proportion of blastocysts at Day 7 appears to be higher than that with fresh oocyte IVF (< 5%) reported previously [6]. We found that 20 cycles (35.1%) had Day 7 blastocysts, which is almost doubled as compared with fresh oocyte IVF (18.5%) [9].…”

“…Although previous studies found that more Day 7 blastocysts were aneuploid as compared with Day 5 or Day 6 blastocysts, suggesting that slow growing embryos may be resulted from oocyte aneuploidy [6,9,11,12]. In the present study, 16 cycles had blastocyst biopsy for preimplantation genetic testing for aneuploidies (PGT-A), and a total of 51 blastocysts (13 at Day 5, 31 at Day 6 and 7 at Day 7) were biopsied.…”

“…Acceptable live birth rates have been obtained after Day 7 blastocyst transfers [6][7][8][9][10]. However, all of the data in these previous reports were from autologous and fresh donor oocyte IVF.…”

“…Delayed embryo development is very often in human IVF even fresh oocytes are used, which is indicated by a delayed blastocyst formation. Day 7 blastocyst accounts for~5-8% of total blastocysts [6]. Although most human IVF laboratories culture human embryos to Day 6, an extended Day 7 culture is necessary for some patients, especially if patients have limited number of oocytes [6][7][8].…”

“…Day 7 blastocyst accounts for~5-8% of total blastocysts [6]. Although most human IVF laboratories culture human embryos to Day 6, an extended Day 7 culture is necessary for some patients, especially if patients have limited number of oocytes [6][7][8]. It has been reported that Day 7 blastocysts had lower implantation potential as compared with Day 5/6 blastocysts, however, transfer of Day 7 blastocysts can lead to acceptable live birth rates [9,10].…”