Non-invasive methods for embryo selection

Abstract

With the widespread use of assisted reproduction, a simple and practical method for embryo selection is needed to optimize the chances of pregnancy while diminishing the incidence of multiple pregnancy and its accompanying problems. Many non-invasive methods for embryo selection have been proposed and some are more promising than others. This review summarizes these methods and attempts to evaluate them in the light of the best currently available evidence and to find out whether any of them is ripe for replacing or supplementing the time-honored method of morphological assessment.

Keywords: Embryo selection; metabolomics; morpho-kinetics; non-invasive; oxidative stress; sHLA-G; time lapse monitoring.

Fig. 1

— Embryo scoring at the pronuclear stage (Z1 = equal pronuclei, equal number and size of nucleoli, aligned in both pronuclei at the pronuclear junction, number of nucleoli 3 to 7; Z2 = equal pronuclei, equal number and size of nucleoli, scattered in both pronuclei, number of nucleoli 3 to 7; Z3 = equal pronuclei, equal number and even or (and) uneven size of nucleoli, aligned in one pronucleus at the pronuclear junction, number of nucleoli 3 to 7; Z4 = unequal or separated pronuclei) (from Scott et al., 2000).

Fig. 2

— Grading the embryo at the cleavage stage (from O’Leary et al., 2013)

Fig. 3

— Scoring the embryo at the blastocyst stage (from Gardner et al., 2000)

Fig. 4

— Amino acid depletion/appearance ± SEM by individual human embryos over the compacting 8-cell to morula transition which subsequently formed blastocysts (n = 23), or which arrested in culture prior to cavitation (n = 32). *P < 0.05; **P < 0.01; ***P < 0.001 significance from zero (from Houghton et al., 2002).

Fig. 5

— Spectra of embryo culture media after day 3 and day 5 transfers (from Kirkegaard et al., 2014).