Reduced oxygen concentration during human IVF culture improves embryo utilization and cumulative pregnancy rates per cycle

STUDY QUESTION: Do different oxygen levels during human IVF embryo culture affect embryo utilization, cumulative IVF success rates per cycle and neonatal birthweight?SUMMARY ANSWER: After 2 days of culture, a lower oxygen level (5%) leads to more good-quality embryos and more embryos that can be cryopreserved, and thereby to a higher cumulative live birth rate per cycle when compared to embryo culture in 20% oxygen, while birthweights are similar.WHAT IS KNOWN ALREADY: Several studies have compared IVF outcome parameters after embryo culture in a more physiological level of 5% oxygen and the atmospheric level of 20%. Although there is consensus that embryo development improves in 5% oxygen, effects on pregnancy and live birth rates are mainly seen in blastocyst, but not cleavage-stage transfers. A major drawback of these studies is that only fresh embryo transfers were included, not taking additional frozen-thawed transfers from these cycles into account. This might have underestimated the effects of oxygen level, especially in cleavage-stage embryo transfers. Furthermore, little is known about the effect of oxygen level during culture on birthweight.STUDY DESIGN, SIZE, DURATION: This is a cohort study in 871 consecutive patients who had an IVF cycle between January 2012 and December 2013, and 5-7 years follow-up to allow transfer of frozen-thawed embryos. Based on daily availability of positions in the incubators, all oocytes and embryos of one cycle were allocated to one of the three incubators with traditional ambient oxygen levels (6% CO2 and 20% O2 in air), or to a fourth incubator that was adjusted to have low oxygen levels of 5% (6% CO2, 5% O2 and 89% N2). Embryos were cultured under 5 or 20% oxygen until Day 2 or 3, when embryos were transferred or cryopreserved, respectively. Clinical and other laboratory procedures were similar in both groups.PARTICIPANTS/MATERIALS, SETTING, METHODS: To compare embryo characteristics and (cumulative) pregnancy outcomes between the two oxygen groups, for each patient only the first cycle in the study period was included in the analysis, resulting in 195 cycles in the 5% group (1627 oocytes) and 676 in the 20% oxygen group (5448 oocytes). Embryo characteristics were analysed per cycle and per embryo and were corrected for maternal age, cycle rank order, fertilization method (IVF or ICSI) and cause of subfertility. Perinatal data from the resulting singletons (n = 124 after fresh and 45 after frozen-thawed embryo transfer) were collected from delivery reports from the hospitals or midwife practices.MAIN RESULTS AND THE ROLE OF CHANCE: In the 5% oxygen group, there were significantly more embryos of good quality (45.8 versus 30.9% in the 20% group, adjusted odds ratio (OR) [95% CI] = 1.9 [1.6-2.4]). This did not result in higher live birth rates per cycle, but after fresh transfers more good-quality spare embryos could be cryopreserved (46.1 versus 29.7%, adjusted OR [95% CI] = 2.0 [1.7-2.5]). After a follow-up period of 5-7 years, in which 82.4% of the cryopreserved embryos from the 5% oxygen group and 85.4% from the 20% oxygen group were thawed, the percentage of patients with at least one live birth resulting from the study cycle was significantly higher in the low oxygen group (adjusted OR [95% CI] = 1.5 [1.01-2.2]). In 124 live born singletons from fresh embryo transfers and in 45 from transfers of cryopreserved embryos, birthweight was similar in both oxygen groups after correction for confounding factors.LIMITATIONS, REASONS FOR CAUTION: This is a retrospective study, and treatment allocation was not randomised. The study was not powered for a predefined birthweight difference. With the number of live births in our study, small differences in birthweight might not have been detected. The selection of embryos to be cryopreserved was based on embryo morphology criteria that might be different in other clinics.WIDER IMPLICATIONS OF THE FINDINGS: Improved embryo utilization by more cryopreservation leading to higher cumulative live birth rates per cycle favours the use of 5% instead of 20% oxygen during human IVF embryo culture. This study also demonstrates that for comparison of different IVF treatment regimens, the cumulative outcome, including transfers of fresh and frozen-thawed embryos, is to be preferred instead of analysis of fresh embryo transfers only.STUDY FUNDING/COMPETING INTEREST(S): No external funding was received for this study. None of the authors has a conflict of interest to declare.</p

Assisted Reproductive Technologies

Since the birth of Louise Brown, the first “test tube baby, " in 1978, assisted reproductive technology (ART) has been widely implemented as a standard treatment for couples with subfertility problems. An estimated 8 million children have been born via ART worldwide and up to 6% of newborns in Europe and 1.5% in United States are conceived via this technique [2]. ART pregnancies are at an increased risk for neonatal complications such as preterm birth and low birth weight as well as maternal complications such as gestational diabetes and preeclampsia. The exact mechanism behind the adverse outcomes is not known, but a role for the placenta is likely. In this chapter we will summarize current knowledge on human placenta development and functioning in relation to ART treatments. We will focus on morphology, vascularization, immunology, placental biomarkers, and aneuploidies

During IVF treatment patient preference shifts from singletons towards twins but only a few patients show an actual reversal of preference

BACKGROUND: Knowledge of patients' preferences for elective single embryo transfer (eSET) or double embryo transfer (DET) and for singletons or twins is of great importance in counselling for embryo transfer (ET) strategies. In this study, the stability of IVF patients' preferences over time for either a healthy single child or healthy twins was measured and we investigated which factors could explain preference shifts. METHODS: Infertile women (n = 177) who participated in an RCT comparing one cycle eSET with one cycle DET were included. A satisfaction questionnaire was developed to measure patient preferences and attitudes at two moments in time, i.e. at 2 weeks before ET and at 2 weeks following ET, after the results of the pregnancy test. Regression analysis examined the effect of several variables on preference shifts. RESULTS: Before ET, most patients expressed a preference for a singleton, whereas most patients were indifferent 2 weeks after ET, resulting in an overall preference shift towards twins (P = 0.002; n = 145). Overall, 62% of patients showed a preference shift. Preference shifts were explained by patients' global satisfaction of the information given by the fertility clinic staff received by the fertility clinic staff, and an interaction between the occurrence of pregnancy and transfer policy (eSET or DET). CONCLUSIONS: In general, patients' preferences for a singleton or twins are not stable during IVF treatment. Possible explanations of a shift in preference are that pregnant patients attuned their preferences to what they expect their pregnancy to result in, whereas non-pregnant patients shifted towards a preference for twins in order to be able to fulfil their ultimate child wish