Oxygen tension in embryo culture: does a shift to 2% O2 in extended culture represent the most physiologic system?

Abstract

There has been much debate regarding the optimal oxygen tension in clinical embryo culture. The majority of the literature to date has compared 5% oxygen to atmospheric levels (20-21%). While the majority of modern IVF labs have accepted the superiority of 5% oxygen tension, a new debate has emerged regarding whether a further reduction after day 3 of development represents the most physiologic system. This new avenue of research is based on the premise that oxygen tension is in fact lower in the uterus than in the oviduct and that the embryo crosses the uterotubal junction sometime on day 3. While data are currently limited, recent experience with ultra-low oxygen (2%) after day 3 of development suggests that the optimal oxygen tension in embryo culture may depend on the stage of development. This review article will consider the current state of the literature and discuss ongoing efforts at studying ultra-low oxygen tension in extended culture.

Keywords: Blastocyst transfer; Embryo culture; Extended culture; In vitro fertilization; Oxygen tension.

Figures

Fig. 1

Oxygen tension in the female reproductive tract. Data from primate models suggest that the oxygen tension in the uterus is lower (approximately 2%) than that in the oviduct (5–7%). If the embryo crosses the uterotubal junction around the time of compaction, then a physiologic culture system will reduce the oxygen concentration after day 3 of development

Fig. 2

Shifting metabolic strategy of the preimplantation embryo. A change in oxygen tension at time of compaction would be consistent with a general shift in the metabolic strategy of the embryo at time of embryonic genome activation