Culture systems: physiological and environmental factors that can affect the outcome of human ART

Seasonal fluctuation of in vitro fertilization encounters in the United States

PURPOSE

To examine patient and hospital characteristics related to seasonal fluctuation in in vitro fertilization (IVF).

METHODS

This retrospective cohort study examined 33,077 oocyte retrievals identified in the National Ambulatory Surgery Sample. Exposure assignment was monthly IVF encounters: low-volume months (<25%ile), mid-volume months (≥25/<75%ile), and high-volume months (>75%ile). Main outcomes were patient and hospital characteristics related to the exposure groups, assessed with a multinomial regression model.

RESULTS

The median IVF encounters were 977 per month, ranging from 657 to 1074 (absolute-difference 417). January, July, and December were the lowest-quartile volume months, ranging from 657 to 710 encounters per month (low-volume months). May, August, and November were the top-quartile volume months, ranging from 1049 to 1074 encounters per month (high-volume months). In a multivariable analysis, patients undergoing IVF in the low-volume months were younger and less likely to have infertility or comorbidities. Patients undergoing IVF in the high-volume months were more likely to have lower household income and receive IVF at urban teaching facilities. Northeastern residents were less likely to have IVF in the low-volume months but more likely to have IVF in the high-volume months. Sensitivity analyses showed that the lowest-to-highest variability in monthly IVF encounters was higher in Northeast region compared to other regions (320 vs 50-128); infertility patients compared to those without (317 vs 190); privately insured patients compared to self-pay (227 vs 156); and older patients compared to younger (234 vs 192).

CONCLUSION

This study suggests substantial seasonal fluctuation in IVF oocyte retrieval in the USA based on patient and hospital factors.

Back to the future: optimised microwell culture of individual human preimplantation stage embryos

Although in vitro culture of human embryos is a crucial step in assisted reproduction, the lack of focused research hampers worldwide standardisation and consistent outcomes. Only 1.2% of research papers published in five leading journals in human reproduction in 2019 focused on in vitro culture conditions, creating the impression that the optimisation process has approached its limits. On the other hand, in vitro culture of mammalian embryos is based on old principles, while there is no consensus on basic issues as density, time, medium change, gas atmosphere and small technical details including the way of drop preparation. This opinion paper aims to highlight and analyse the slow advancement in this field and stimulate research for simple and affordable solutions to meet the current requirements. A possible way for advancement is discussed in detail. Selection of embryos with the highest developmental competence requires individual culture and modification of the widely used "drop under oil" approach. Current use of three-dimensional surfaces instead of large flat bottoms is restricted to time-lapse systems, but these wells are designed for optical clarity, not for the needs of embryos. The size and shape of the original microwells (Well of the Well; WOW) offer a practical and straightforward solution to combine the benefits of communal and individual incubation and improve the overall quality of cultured embryos.

Back to the future: optimised microwell culture of individual human preimplantation stage embryos

Although in vitro culture of human embryos is a crucial step in assisted reproduction, the lack of focused research hampers worldwide standardisation and consistent outcomes. Only 1.2% of research papers published in five leading journals in human reproduction in 2019 focused on in vitro culture conditions, creating the impression that the optimisation process has approached its limits. On the other hand, in vitro culture of mammalian embryos is based on old principles, while there is no consensus on basic issues as density, time, medium change, gas atmosphere and small technical details including the way of drop preparation. This opinion paper aims to highlight and analyse the slow advancement in this field and stimulate research for simple and affordable solutions to meet the current requirements. A possible way for advancement is discussed in detail. Selection of embryos with the highest developmental competence requires individual culture and modification of the widely used "drop under oil" approach. Current use of three-dimensional surfaces instead of large flat bottoms is restricted to time-lapse systems, but these wells are designed for optical clarity, not for the needs of embryos. The size and shape of the original microwells (Well of the Well; WOW) offer a practical and straightforward solution to combine the benefits of communal and individual incubation and improve the overall quality of cultured embryos.

Gelatin Electrospun Mat as a Potential Co-culture System for In Vitro Production of Sperm Cells from Embryonic Stem Cells

Engineering of 3D substrates with maximum similarity to seminiferous tubules would help to produce functional sperm cells in vitro from stem cells. Here, we present a 3D electrospun gelatin (EG) substrate seeded with Sertoli cells and determine its potential for guided differentiation of embryonic stem cells (ESCs) toward germline cells. The EG was fabricated by electrospinning, and its morphology under SEM, as well as cytobiocompatibility for Sertoli cells and ESCs, was confirmed by 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyl tetrazolium bromide and cell attachment assay. Embryoid bodies (EBs) were formed from ESCs and co-cultured with Sertoli cells, induced with BMP4 for 3 and 7 consecutive days to induce the differentiation of EBs toward germline cells. The differentiation was investigated by immunocytochemistry (ICC), flow cytometry, and RT-PCR in four experimental groups of EBs (EBs cultured in gelatin-coated cell culture plates); Scaffold/EB (EBs cultured on EG); ESCs/Ser (EBs and Sertoli cells co-cultured on gelatin-coated cell culture plates without EG); and Scaffold/EB/Ser (EBs and Sertoli cells co-cultured on EG). All experimental groups exhibited a significantly increased MVH (germline-specific marker) and decreased c-KIT (stemness marker) expression when compared with the EB group. ICC and flow cytometry revealed that Scaffold/EB/Ser had the highest level of MVH and the lowest c-KIT expression at both 3 and 7 days postdifferentiation compared with other groups. RT-PCR results showed a significant increase in the germline marker (Dazl) and a significant decrease in the ESC stemness marker (Nanog) in Scaffold/EB compared to the EB group. The germline markers Gcna, Stella, Mvh, Stra8, Piwil2, and Dazl were significantly increased in Scaffold/EB/Ser compared to the Scaffold/EB group. Our findings revealed that the EG scaffold can provide an excellent substrate biomimicking the micro/nanostructure of native seminiferous tubules and a platform for Sertoli cell-EB communication required for growth and differentiation of ESCs into germline cells.

Female Reproductive Performance and Maternal Birth Month: A Comprehensive Meta-Analysis Exploring Multiple Seasonal Mechanisms

Globally, maternal birth season affects fertility later in life. The purpose of this systematic literature review is to comprehensively investigate the birth season and female fertility relationship. Using PubMed, we identified a set of 282 relevant fertility/birth season papers published between 1972 and 2018. We screened all 282 studies and removed 131 non-mammalian species studies on fertility and 122 studies that were on non-human mammals. Our meta-analysis focused on the remaining 29 human studies, including twelve human datasets from around the world (USA, Europe, Asia). The main outcome was change in female fertility as observed by maternal birth month and whether this change was correlated with either temperature or rainfall. We found that temperature was either strongly correlated or anti-correlated in studies, indicating that another factor closely tied to temperature may be the culprit exposure. We found that rainfall only increases fertility in higher altitude locations (New Zealand, Romania, and Northern Vietnam). This suggests the possibility of a combined or multi-factorial mechanism underlying the female fertility - birth season relationship. We discuss other environmental and sociological factors on the birth season - female fertility relationship. Future research should focus on the role of birth season and female fertility adjusting for additional factors that modulate female fertility as discussed in this comprehensive review.