Maternal aging adversely affects oocyte quality (function and developmental potential) and consequently lowers pregnancy rates while increasing spontaneous abortions. Substantial evidence, especially from egg donation studies, implicates the decreased quality of an aging oocyte as a major factor in the etiology of female infertility. Nevertheless, the cellular and molecular mechanisms responsible for the decreased oocyte quality with advanced maternal aging are not fully characterized. Herein we present information in the published literature and our own data to support the hypothesis that during aging induced decreases in mitochondrial ceramide levels and associated alterations in mitochondrial structure and function are prominent elements contributing to reduced oocyte quality. Hence, by examining the molecular determinants that underlie impairments in oocyte mitochondria, we expect to sieve to a better understanding of the mechanistic anatomy of oocyte aging.
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- Abstract: IVM x
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- Abstract: fertility preservation x
- Abstract: preimplantation genetic diagnosis x
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Loro L Kujjo and Gloria I Perez
B. A. Keel, B. W. Webster, and D. K. Roberts
Summary. Ejaculates (164) were obtained from 17 donors serving on an artificial insemination by donor panel. Semen analysis was performed before and after freezing by an integrated microcomputerized system employing the multiple-exposure photography (MEP) method. Sperm count, motility, velocity, motility index (MI; product of the sperm velocity and percentage of motile spermatozoa) and motile density (MD) were determined for each ejaculate. After the initial evaluation the ejaculates were frozen in liquid nitrogen, thawed 24 h later, and assessed for post-thaw motility, velocity, MI and MD. The mean ± s.e. sperm count and volume for this group of donors was 148 ± 4 × 106/ml and 3·1 ± 0·1 ml, respectively. Mean ± s.e. values obtained from the prefreeze analysis were: motility = 64 ± 1%, velocity = 30 ± 0·4μm/sec, MI = 19 ± 0·5 μm/sec and MD = 94 ± 3 × 106/ml. Post-thaw analysis revealed a significant reduction (P < 0·01 in all values measured. Motility was reduced to 27 ± 1%, MI was reduced to 5 ± 0·3 μm/sec, and MD was reduced to 33 ± 1 × 106/ml Velocity was the least affected by cryopreservation, being reduced to 21 ± 0·5 μm/sec (P < 0·01). Cryopreservation resulted in a marked shift in the frequency distribution of sperm motility and motility index towards subnormal values while in the majority of ejaculates velocity and motile density were maintained in the normal range. Significant differences were noted amongst donors in the percentage change of the various semen measures as a result of cryopreservation. When within-subject coefficients of variation were calculated, velocity was the least variable parameter. These results indicate that, while cryopreservation results in significant reductions in the number of motile spermatozoa in the ejaculate, the velocity is only marginally reduced.
E. A. McLaughlin, W. C. L. Ford, and M. G. R. Hull
Summary. The motility characteristics of washed spermatozoa from 50 normal ejaculates were measured by time-lapse photography, before and after cryopreservation. Plasma membrane integrity was assessed by the hypo-osmotic swelling test and with the supravital fluorescent dye bisbenzimide (H33258).
There was a marked decline in the percentage of progressively motile spermatozoa after cryopreservation, the extent varying widely among donors. Results were, however, consistent between different ejaculates from the same individual. The ability of spermatozoa to survive cryopreservation could not be predicted from the properties of the semen beforehand.
The mean velocity of the spermatozoa was significantly reduced after freezing, but the lateral head displacement was unaltered. There was a significant reduction in the proportion of spermatozoa with intact plasma membranes after cryopreservation and the results of the hypo-osmotic swelling test and H33258 tests correlated closely. There was no correlation between the declines in the percentage of motile spermatozoa, or intact spermatozoa and the sperm velocity.
We conclude that membrane rupture is not the sole cause of loss of motile spermatozoa during freezing and that the decrease in the proportion of motile spermatozoa is caused, at least in part, by a separate process from that responsible for the decrease in the average swimming speed of spermatozoa.
Keywords: spermatozoa; cryopreservation; motility; membranes; semen; donor insemination; human
A. A. Templeton, P. Van Look, R. E. Angell, R. J. Aitken, M. A. Lumsden, and D. T. Baird
Summary. Volunteer women requesting laparoscopic sterilization were subjected to a fixed schedule of ovulation induction and oocyte recovery. Follicle aspiration was carried out in four groups: those to whom hCG was not administered and 12, 24 or 36 h respectively after the administration of hCG. For each group oocytes were cultured in vitro for 42 h, 30 h, 18 h and 6 h respectively, before insemination with donor spermatozoa. Oocyte recovery rates improved with longer hCG-to-recovery intervals (36% with no hCG to 81% 36 h after hCG). Although there was a slight reduction in fertilization rates when oocytes were not exposed to hCG in the follicle, normal cleavage was noted in more than 50% of oocytes in all four groups. It therefore appears that the final maturation stages of the human oocyte are not dependent on the midcycle gonadotrophin surge, provided the oocyte is matured in vitro before insemination. However, it was also evident that the fertilization rates were reduced when oocytes were removed from less mature follicles, as reflected by high androstenedione/ oestradiol ratios.
E. A. McLaughlin, W. C. L. Ford, and M. G. R. Hull
Summary. The contribution of the toxicity of glycerol–egg yolk–citrate (GEYC) cryopreservative medium to the loss of function of human spermatozoa during cryopreservation was determined by investigating the effect of mixing semen with the medium on sperm motility. The percentage of progressively motile spermatozoa, velocity (μm s−1) and lateral head displacement (μm) (mean ± sem, n = 28) were 55 ± 4·1, 47 ± 2·7, 4·4 ± 0·2 and 32 ± 3·8, 40 ± 2·5, 3·6 ± 0·25 and 15 ± 2·5, 28 ± 1·1, 2·8 ± 0·15 in suspensions of washed spermatozoa prepared from fresh, GEYC-treated and frozen–thawed semen, respectively. The variables changed only slightly after incubation for 3 h. The toxicity of GEYC did not vary significantly between samples which survived the complete freeze–thaw cycle well or very poorly. The toxicity of GEYC is responsible for about 50% of the loss of progressively motile spermatozoa during the complete cryopreservation process, but has little effect on the quality of motility. Susceptibility to GEYC does not explain observed differences in the ability of semen samples to survive freezing.
Keywords: cryopreservation; spermatozoa; motility; glycerol; donor insemination; human
S. Samaké and L. C. Smith
The methods used to achieve blastomere cell cycle synchronization in embryos used as nuclear donors during embryo reconstruction have been largely unsuccessful. The aim of this study was to determine the reliability of 6-dimethylaminopurine (6-DMAP), an inhibitor of maturation promoting factor, to halt and to synchronize blastomere division in cleavage stage bovine embryos. A second goal was to assess its reversibility and toxicity in vitro. Eight-cell stage embryos obtained at 58 h after insemination were treated with several concentrations of 6-DMAP for 12 h. Treated embryos were assessed for cleavage arrest, chromatin morphology, DNA synthesis, histone H1 and scored for blastocyst formation and for hatching rate. They were subsequently fixed and the number of nuclei counted. Complete arrest of cell division was observed at concentrations of 3 mmol 6-DMAP l−1 and above. At these concentrations, interphase nuclei in arrest were noticeably larger compared with interphase nuclei of eight-cell control embryos. Removal from 6-DMAP led to release from cleavage arrest and was followed by synchronized mitosis, histone H1 kinase deactivation and re-entry into interphase within 4–5 h. Twenty-nine per cent of interphase nuclei were synthesizing DNA at the end of the 12 h treatment as indicated by BrdU analysis. At 2 h after removal from 6-DMAP, an abrupt decrease to 9% BrdU-positive nuclei was observed followed by an increase to 39% by 6 h and a decrease to 28% at 10 h. The ability of treated embryos to reach the blastocyst stage in vitro and the number of cells per blastocyst were reduced. These results indicate that 6-DMAP can reversibly arrest and synchronize cleavage to the fifth cell cycle in eight-cell bovine embryos. Although a decrease was observed in the proportion of blastocysts obtained after treatment, it is concluded that 6-DMAP is a useful tool for synchronization studies requiring donor nuclei at metaphase before fusion to recipient oocyte.
J. M. Sreenan and T. McDonagh
Summary. In Exp. 1, embryo survival rates of 45 and 47% were recorded after artificial insemination and ipsilateral transfer respectively. In Exp. 2, pregnancy rates of 62 and 60% were recorded after artificial insemination and contralateral transfer to inseminated recipients respectively. In this experiment the contralateral transferred embryo survival rate was 44%. Transferred embryo survival was lower overall when donors and recipients were out of phase by 1 day than when exactly synchronous.
Darren K Griffin and Cagri Ogur
Designed to minimize chances of transferring genetically abnormal embryos, preimplantation genetic diagnosis (PGD) involves in vitro fertilization (IVF), embryo biopsy, diagnosis and selective embryo transfer. Preimplantation genetic testing for aneuploidy (PGT-A) aims to avoid miscarriage and live born trisomic offspring and to improve IVF success. Diagnostic approaches include fluorescence in situ hybridization (FISH) and more contemporary comprehensive chromosome screening (CCS) including array comparative genomic hybridization (aCGH), quantitative polymerase chain reaction (PCR), next-generation sequencing (NGS) and karyomapping. NGS has an improved dynamic range, and karyomapping can detect chromosomal and monogenic disorders simultaneously. Mosaicism (commonplace in human embryos) can arise by several mechanisms; those arising initially meiotically (but with a subsequent post-zygotic ‘trisomy rescue’ event) usually lead to adverse outcomes, whereas the extent to which mosaics that are initially chromosomally normal (but then arise purely post-zygotically) can lead to unaffected live births is uncertain. Polar body (PB) biopsy is the least common sampling method, having drawbacks including cost and inability to detect any paternal contribution. Historically, cleavage-stage (blastomere) biopsy has been the most popular; however, higher abnormality levels, mosaicism and potential for embryo damage have led to it being superseded by blastocyst (trophectoderm – TE) biopsy, which provides more cells for analysis. Improved biopsy, diagnosis and freeze-all strategies collectively have the potential to revolutionize PGT-A, and there is increasing evidence of their combined efficacy. Nonetheless, PGT-A continues to attract criticism, prompting questions of when we consider the evidence base sufficient to justify routine PGT-A? Basic biological research is essential to address unanswered questions concerning the chromosome complement of human embryos, and we thus entreat companies, governments and charities to fund more. This will benefit both IVF patients and prospective parents at risk of aneuploid offspring following natural conception. The aim of this review is to appraise the ‘state of the art’ in terms of PGT-A, including the controversial areas, and to suggest a practical ‘way forward’ in terms of future diagnosis and applied research.
JAN RABOCH and ZD. TOMáŠEK
The authors performed therapeutic donor insemination in 219 women. In 114 cases, 132 conceptions were obtained. The average number of inseminations for one conception was 3·8. More than half of the women in the `unsuccessful' subgroup did not exhaust the therapeutic possibilities of this treatment, i.e. aid extending over the period of five to six cycles. Seventeen losses in pregnancy, or within 10 days after delivery, correspond to less than 13%. One boy out of 108 living children (fifty boys and fifty-eight girls) had a developmental anomaly (penile hypospadias).
Alan H Handyside
The first pregnancies and live births following in vitro fertilisation (IVF) and preimplantation genetic testing (PGT), formerly known as preimplantation genetic diagnosis, were reported in 1990, almost 30 years ago, in several couples at risk of X-linked inherited conditions, which typically only affect boys inheriting the X chromosome with the affected gene from their carrier mothers. At that time, it was only possible to identify the sex of the embryo by amplifying a Y-linked repeat sequence in single cells biopsied at cleavage stages and avoid the transfer of males, half of which would be affected. The extensive publicity surrounding these cases and the perceived risk of using IVF and PGT for desirable characteristics not related to health, such as sex selection, led to the epithet of ‘designer babies’ which continues to resonate to this day. Here, I briefly reflect on how the technology of PGT has evolved over the decades and whether it deserves this reputation. With efficient methods for whole genome amplification and the genomic revolution, we now have highly accurate universal tests that combine marker-based diagnosis of almost any monogenic disorder with the detection of aneuploidy. PGT is now clinically well established and is likely to remain a valuable alternative for couples at risk of having affected children.