Evaluation of the Impact of Reduced Oxygen Concentration on Live Birth Rate
Condition: Infertility
MeSH terms: Infertility
Study type: Interventional

Summary: 
      Clinical in vitro fertilization relies on successful embryo culture. The primary goal of
      embryo culture is to attempt to recapitulate the in vivo conditions as much as possible. In
      the past decade, the majority embryo culture has been performed at 5% oxygen due to the
      discovery that the oxygen tension in the fallopian tube (where the embryo is located for the
      first 3 days after fertilization) is 5%. However, relatively recent studies have demonstrated
      that the oxygen tension in the uterus (where the embryo is located after day 3) is closer to
      2%. This study is a randomized controlled trial that will compare pregnancy rates between
      embryos cultured in 2% versus 5% after day 3 of development.
    

Detailed description: 
      Significant progress has been made in characterizing the optimal environment for a developing
      embryo in culture. These efforts have been based on the premise that clinical embryo culture
      should mimic the in vivo environment. To this end, investigators have gone to great lengths
      to recreate every aspect of the natural setting to which the early embryo is exposed. This
      focused approach has led to significant modifications of the embryo culture system in the
      modern in vitro fertilization (IVF) lab and ultimately to improvements in pregnancy rates.

      One area that has been subject to significant scrutiny is the relationship between incubator
      oxygen concentration and early embryonic development. Oxygen plays a central role in
      embryonic metabolism. The mechanism governing its utilization is dependent on the stage of
      embryonic development. During the first 3 days of development, oxygen reaches the embryo via
      passive diffusion and its concentration gradient is regulated by oxygen consumption during
      oxidative phosphorylation. Inefficiencies in this process - due to compromised integrity of
      the inner mitochondrial membrane or alterations in substrate availability - can result in
      excessive production of harmful reactive oxygen species which can cause significant damage to
      cellular machinery and ultimately lead to embryonic arrest.

      The concentration of oxygen that the embryo in culture is exposed to can also impact this
      delicately balanced system and alter the metabolic health of an embryo. Historically,
      atmospheric oxygen concentration (approximately 20%) was exclusively used in human IVF
      laboratories for embryo culture. However, multiple investigations subsequently found that the
      physiologic concentration of oxygen within the female reproductive tract is well below
      atmospheric levels, being consistently measured at <10%. These observations led to multiple
      trials comparing atmospheric oxygen concentrations to 5% oxygen in embryo culture. These
      studies demonstrated significant perturbations in gene expression, protein secretion, and
      suboptimal utilization of amino acids and carbohydrates in embryos cultured in atmospheric
      oxygen. The same comparisons were made in clinical IVF studies and demonstrated that embryos
      cultured in 5% oxygen consistently resulted in an increase in clinical pregnancy rate and
      live birth rate. A meta-analysis of this topic suggested that a clinic with a baseline live
      birth rate of 30% could expect an improvement as great as 13% when culturing embryos at 5%
      O2.

      As a result of these compelling data, most modern IVF programs now exclusively culture
      embryos at 5% oxygen concentration. However, some have proposed that the oxygen concentration
      to which the embryo is exposed after day 3 of development is actually lower than 5%. These
      data originate from the idea that the embryo crosses the utero-tubal junction on day 3 of
      development in vivo. Multiple studies have demonstrated that the oxygen concentration in the
      uterus is actually lower than that in the fallopian tube at approximately 2%. Thus, the most
      physiologic embryo culture system would culture embryos in 5% oxygen until day 3 and then
      decrease the oxygen concentration to 2% until transfer or cryopreservation on day 5 or 6.

      A change in the optimal oxygen concentration for an embryo on day 3 would fit with a general
      shift in metabolic requirements of embryos seen at this stage of development. Activation of
      the embryonic genome occurs on day 3 which prompts a significant increase in biosynthetic
      activity. The metabolic behavior of embryos also shifts substantially during this time. The
      embryo changes its metabolic strategy from oxidative phosphorylation to glucose based
      metabolism in the form of the aerobic glycolysis and the citric acid cycle. During this
      process, termed compaction, embryos exhibit greatly increased oxygen consumption.

      The physiologic environment of the female reproductive tract tends to mirror the metabolic
      needs of the developing preimplantation embryo. As the embryo shifts its metabolic strategy
      after compaction and upon entering the uterus, it is certainly possible that a reduced oxygen
      concentration in the uterus may best support the energy producing mechanisms of this stage in
      embryonic development. Recapitulating this environment in culture may enhance embryonic
      development and long term health of pregnancies resulting from IVF.

      This theory has been corroborated in two recent pilot studies. The first study, recently
      awarded the Prize Paper Award at the 2016 American Society for Reproductive Medicine
      Scientific Meeting, randomized embryos donated to research to 2% or 5% oxygen concentration
      after day 3 of development and found that embryos were twice as likely to blastulate if they
      were cultured in 2% oxygen concentration. However, embryos studied in this investigation were
      either abnormally fertilized or warmed from cryopreservation on day 3 after being donated to
      research. None were intended for clinical use.

      With these limitations in mind, our group has recently completed a study utilizing embryos
      intended for clinical use (Copernicus IRB: RMA-2016-02). In this study, we enrolled 60
      patients and split all ongoing embryos on day 3 of development to culture in either 2% or 5%
      oxygen until the blastocyst stage. The results have not yet been published, but culture in 2%
      oxygen after day 3 produced more blastocysts than culture in 5% oxygen. In total, 30 patients
      had more embryos reach blastocyst in 2% oxygen, while only 17 patients had more embryos reach
      blastocyst in 5% oxygen. Ten patients had an equal number in both conditions (3 withdrew from
      the study). This difference reached statistical significance.

      This initial study was designed to specifically evaluate the developmental performance of
      embryos in both conditions. However, there are also some pregnancy data available from those
      patients who have proceeded to transfer these embryos. In this initial study, culture
      conditions had no impact on the decision of which embryo to transfer. This was blinded to
      embryologists and patients and only typical morphology criteria were utilized. Again, of
      patients who have proceeded to embryo transfer, embryos that had been cultured in 2% oxygen
      have performed better than those exclusively in 5% (88.9% [16/18] vs. 62.5% [15/24]

      However, this initial study was not designed to specifically test the question of whether 2%
      versus 5% oxygen in extended culture produces better pregnancy outcomes. The patients were
      not randomized to either 2% or 5% oxygen. Thus, current pregnancy data is prone to some bias
      and a better controlled study is needed evaluate the impact of reduced oxygen concentration
      in culture on the most important outcomes: live birth rate.

      Purpose of Proposed Study This study seeks to compare clinical outcomes of embryos cultured
      at 2% oxygen concentration and 5% oxygen concentration after compaction. The primary outcome
      under study will be live birth rate. Secondary outcomes will include miscarriage rate,
      gestational age at delivery, birth weight at delivery, embryo blastulation rate, embryo
      ploidy status (aneuploid or euploid) and morphologic parameters (expansion, inner cell mass
      grade, trophectoderm grade). The cumulative live birth rate of all embryos that originate
      from the study stimulation cycle will also be collected and analyzed. This will theoretically
      reveal whether any advantage in the number of available blastocysts for transfer translates
      to greater reproductive efficiency when extended culture is performed at 2% oxygen.
    

Intervention name(s): 2% Oxygen
Intervention type(s): Other
Intervention description(s): 2% oxygen concentration in the incubator in which embryos are being cultured after day 3 of development
Allocation: Randomized
Intervention model: Parallel Assignment
Intervention model description: Randomized Controlled Trial
Masking: Triple (Participant, Care Provider, Investigator)
Primary purpose: Treatment