Binucleated and micronucleated blastomeres in embryos derived from human assisted reproduction cycles

This prospective sequential, cohort study examined the two most common multinucleation phenotypes observed in the authors' clinic, binucleated (BN) and micronucleated (MN) blastomeres, and included all intracytoplasmic sperm injection (ICSI) patients <40 years of age with at least one multinucleated embryo in the cohort as observed on day 2 of development. Eighty ICSI cycles of 560 consecutive cycles had multinucleated embryos (14.3%). Of the 80 cycles, 770 embryos were derived; 183 (23.8%) were observed to be multinucleated. Blastocyst rates were significantly higher with BN than MN embryos. MN embryos were more often derived from embryos with poor pronuclear morphology (41/81 = 50.6%). Transferred mononucleated sibling embryos from the BN group had an ongoing pregnancy rate of 48% (12/25) compared with 15.4% (4/26 from the group with MN embryos (P = 0.03). The implantation rate for sibling embryos from the BN group was higher than for those from the MN group. Fluorescence in-situ hybridization (FISH) analysis showed that BN embryos had normal blastomeres significantly more frequently than MN embryos (9/28 (32.1%) versus 1/27 (3.7%), P = 0.016). Time-lapse photography showed that the nuclei of both morphologies dissolved independently before the next mitotic division and that BN blastomeres definitely have two distinct nuclei. These observations indicate two diverse morphologies and causal mechanisms. Time-lapse photography showed that both were subject to independent dissolution of their nuclear membrane suggesting an asynchrony between the nuclei and a possible interruption in proper nuclear and cell division. Multinucleation should definitely be looked for during IVF assessment. Excluding these embryos from transfer is prudent practice.

Randomized controlled study of human zona pellucida dissection using the zona infrared laser optical system: evaluation of blastomere damage, embryo development, and subsequent hatching

OBJECTIVE

To assess the effect of laser hatching on human embryo damage and subsequent development using the Zona Infrared Laser Optical System (ZILOS).

DESIGN

Randomized controlled study.

SETTING

Tertiary care fertility clinic.

PATIENT(S)

One hundred fourteen donated and discarded frozen human embryos.

INTERVENTION(S)

Embryos were thawed, cultured with cleavage and morphology evaluated periodically, and randomized into control, partial hatching, or complete hatching groups. The laser hatching procedure was performed by ZILOS. Zona thickness and embryo diameter were recorded. Complete hatching involved the production of a full-thickness defect in the zona and partial hatching, a defect in the outer half of the zona. No laser treatment was administered to the control group.

MAIN OUTCOME MEASURE(S)

Blastocyst development and completion of hatching process.

RESULT(S)

No significant difference was noted between the three study groups for their baseline characteristics. There was no significant difference in blastocyst development among the three groups. However, the complete hatching group showed a significant increase in hatching compared to the control group.

CONCLUSION(S)

Complete laser hatching of human embryos using the ZILOS does not have an adverse effect on subsequent development and increases the rate of completion of hatching.

Effect of blastomere loss on the outcome of frozen embryo replacement cycles

OBJECTIVE

To assess the impact of survival of cryopreservation and thawing with all blastomeres intact on the outcome of frozen embryo replacement (FER) cycles.

DESIGN

Prospective observational study.

SETTING

University-affiliated tertiary referral assisted conception unit.

PATIENT(S)

The number of intact blastomeres before cryopreservation and after thawing was prospectively recorded in 1,687 cleavage-stage embryos thawed in 377 FER cycles. The cycles were categorized into two groups: group A (n = 184) included cycles in which all embryos transferred survived the cryopreservation and thawing process with all their original blastomeres intact; group B (n = 193) included cycles in which embryos transferred included at least one partially damaged embryo that has lost up to 50% of its original blastomere number.

INTERVENTION(S)

None.

MAIN OUTCOME MEASURE(S)

Pregnancy and embryo implantation rates.

RESULT(S)

Groups A and B were comparable with respect to mean age at cryopreservation, mean number of oocytes retrieved and fertilized normally in the fresh cycle, and mean age at frozen transfer. No significant difference was found between the two groups with regard to mean number of frozen and thawed embryos per cycle and mean endometrial thickness reached before P supplementation. More embryos were transferred per cycle in group B than group A (2.4 +/- 0.6 vs. 2.1 +/- 0.6, respectively). However, the pregnancy and clinical pregnancy rates per cycle were significantly higher in group A than in group B (39.1% and 28.3% vs. 22.8% and 13.5%, respectively). The implantation rate was also higher in group A than in group B (17.3% vs. 8.1%, respectively).

CONCLUSION(S)

FER cycles in which all embryos transferred remained fully intact at thawing achieve a better outcome than those with at least one partially damaged embryo.

Results of preimplantation genetic diagnosis in patients with Klinefelter's syndrome

With the application of preimplantation genetic diagnosis (PGD), a possible genetic contribution of spermatozoa obtained from 47,XXY non-mosaic Klinefelter patients on preimplantation embryos was analysed in eight couples. Interpretable fluorescence in-situ hybridization results were obtained for 28 out of 33 embryos biopsied (84.8%) and 23 blastomeres were analysed for chromosomes 13, 18, 21, X and Y. Nine out of 23 embryos were diagnosed as abnormal (39.1%). Five out of nine contained sex chromosome abnormalities (55.5%). Two were diagnosed as 47,XXY and three were found to have monosomy X. Besides sex chromosomal abnormalities, other abnormalities detected were haploidy, triploidy, monosomy 13, monosomy 18 and trisomy 13. Five blastomeres were analysed for sex chromosomes only and all of them were found to be normal. Overall, the rate of sex chromosome abnormality in biopsied embryos was found to be 17.8% (5/28). Moreover, among 33 embryos biopsied, five of the eight zygotes, which were classified as a poor prognosis group according to pronuclear morphology scoring, showed an impaired growth profile after biopsy and were found to be chromosomally abnormal. Elimination of abnormal embyos and transfer of normal ones resulted in four pregnancies in eight cycles (50%). Two pregnancies, one singleton and one twins resulted in healthy births. Two pregnancies, one singleton and one twins are continuing beyond the second trimester. These results show that there is in fact elevated chromosomal abnormality for both sex chromosomes and autosomes in embryos developed from Klinefelter males. Furthermore together with PGD, embryo scoring according to pronuclear morphology can give additional benefit for selecting chromosomally abnormal embryos. Therefore, PGD should be recommended in cases with Klinefelter's syndrome and this information should be discussed with the couple when genetic counselling is given.

Chromosome abnormalities identified by comparative genomic hybridization in embryos from women with repeated implantation failure

Using comparative genomic hybridization, we have detected chromosome abnormality in 76/126 (60%) single blastomeres biopsied prior to implantation from embryos from 20 women with repeated implantation failure following IVF. The abnormalities detected included aneuploidy for one or two chromosomes [32/126 (25%)] and complex chromosomal abnormality [37/126 (29%)]. Most of the chromosomes involved in single aneuploidy were those commonly found in live births or spontaneously aborted fetuses, whereas a greater range of chromosomes were involved in double aneuploidy. In blastomeres with complex abnormality, random and extensive loss and gain of all the chromosomes was observed. Further blastomeres from 25 embryos with single or double aneuploidy and 11 embryos with complex abnormality were analysed following embryo disaggregation. The specific abnormality was confirmed in the majority of cases and in some cases could be assigned as errors in meiotic or mitotic segregation. Complex abnormalities, suggestive of errors in cell cycle regulation, were present in a slightly higher proportion of these embryos than were seen in our previously studied cohort of surplus embryos. The disruption of the normal sequence of chromosome replication and segregation in early human embryos, caused either by maternal cytoplasmic factors or mutations in cell cycle control genes, may be a common cause of repeated implantation failure.

First clinical application of comparative genomic hybridization and polar body testing for preimplantation genetic diagnosis of aneuploidy

OBJECTIVE

To develop a preimplantation genetic diagnosis (PGD) protocol that allows any form of chromosome imbalance to be detected.

DESIGN

Case report employing a method based on whole-genome amplification and comparative genomic hybridization (CGH).

SETTING

Clinical IVF laboratory.

PATIENT(S)

A 40-year-old IVF patient.

INTERVENTION(S)

Polar body and blastomere biopsy.

MAIN OUTCOME MEASURE(S)

Detection of aneuploidy.

RESULT(S)

Chromosome imbalance was detected in 9 of 10 polar bodies. A variety of chromosomes were aneuploid, but chromosomal size was found to be an important predisposing factor. In three cases, the resulting embryos could be tested using fluorescence in situ hybridization, and in each case the CGH diagnosis was confirmed. A single embryo could be recommended for transfer on the basis of the CGH data, but no pregnancy ensued.

CONCLUSION(S)

Evidence suggests that preferential transfer of chromosomally normal embryos can improve IVF outcomes. However, current PGD protocols do not allow analysis of every chromosome, and therefore a proportion of abnormal embryos remains undetected. We describe a method that allows every chromosome to be assessed in polar bodies and oocytes. The technique was accurate and allowed identification of aneuploid embryos that would have been diagnosed as normal by standard PGD techniques. As well as comprehensive cytogenetic analysis, this protocol permits simultaneous testing for multiple single-gene disorders.

Laser-assisted removal of necrotic blastomeres from cryopreserved embryos that were partially damaged

OBJECTIVE

To examine whether the developmental potential of embryos that were partially damaged after freezing and thawing can be improved by removal of necrotic blastomeres before embryo transfer.

DESIGN

Prospective pilot study and observational clinical series.

SETTING

Private hospital.

PATIENT(S)

Two hundred thirty-five infertile couples undergoing frozen embryo transfer.

INTERVENTION(S)

Removal of necrotic blastomeres from frozen-thawed human embryos.

MAIN OUTCOME MEASURE(S)

Pregnancy and implantation rates.

RESULT(S)

Removal of necrotic blastomeres from partially damaged frozen-thawed embryos before transfer increased rates of pregnancy (45.7% vs. 17.1%), ongoing pregnancy (40.0% vs. 11.4%) and ongoing implantation (16.2% vs. 4.3%) compared with the control group, in which necrotic blastomeres were not removed. A similarly high implantation rate (16.7%) was seen a subsequent clinical series in which necrotic blastomeres were removed from all partially damaged embryos.

CONCLUSION(S)

The viability of partially damaged frozen-thawed embryos can be improved by removal of necrotic blastomeres before embryo transfer.

Bovine abnormal preimplantation embryos: analysis of segregated cells occurring in the subzonal space and/or blastocoele cavity for their nuclear morphology and persistence of RNA synthesis

Bovine embryos in the early blastocyst/blastocyst stage were analysed by [5-3H]uridine labelling followed by electron microscopic autoradiography. In normal control embryos an intact zona pellucida, evenly developed blastomeres and a transparent perivitelline space were seen. In this group, the blastomeres of the trophoblast and embryoblast showed high homogeneous labelling localised in the nucleoplasm and even more intense labelling in the nucleolus. On the contrary, in addition to evident cytoplasmic disintegration, a clearly different labelling pattern and a low labelling intensity were observed in the nuclei of the segregated cells in the subzonal space and in those free in the blastocoele cavity. A typical nuclear morphological feature of these blastomeres was chromatin marginalisation, similar to that observed in embryos treated with actinomycin D for transcription inhibition. It is concluded that the segregated cells are arrested in their further differentiation.

Expression of apoptosis-related genes in human oocytes and embryos

PURPOSE

The objective was to study whether apoptosis occurs in human embryogenesis.

METHODS

Human viable, arrested, and nonviable embryos and immature, and nonfertilized oocytes donated by our patients were used to detect apoptosis by Tunel labeling, annexin staining, and single-cell reverse transcriptase-polymerase chain reaction (RT-PCR).

RESULTS

DNA fragmentation and phosphotidylserine translocation, the two markers for apoptosis, were detected frequently in fragmented human embryos derived from in vitro fertilization-embryo transfer (IVF-ET). Using RT-PCR, apoptotic genes also were detected in these embryos. The frequencies of gene expression in viable embryos, arrested embryos, nonviable embryos, immature oocytes, and non-fertilized oocytes were: 7/8, 5/5, 5/6, 0/6, 0/3, for Bax; 8/8, 5/5, 7/7, 0/4, 0/5 for Fas; 2/8, 0/2, 0/3, 0/5, 0/3 for BCL-2; 0/8, 1/3, 0/2, 0/3, 0/2 for Fas-ligand; and 8/8, 17/17, 21/21, 24/24, 15/15 for actin, respectively.

CONCLUSIONS

Our preliminary data did not show a significant difference in the expression frequency of all studied genes between viable embryos and nonviable or arrested embryos. However, the expression of Bax and Fas was noticeably higher in nonviable embryos than in viable embryos as judged by the intensities of amplicons visualized after ethidium bromide staining. In addition, BCL-2 was only detected in viable embryos. Whether embryos quality is related to the regulation of BCL-2, Bax, and Fas expressions requires further study.

Clinical pregnancy following blastomere biopsy and PGD for a reciprocal translocation carrier: analysis of meiotic outcomes and embryo quality in two IVF cycles

A couple were referred for preimplantation genetic diagnosis (PGD) following diagnosis of a reciprocal translocation in the female partner: 46,XX,t(14;22)(q11.2;q13.3). PGD was carried out using fluorescence in situ hybridization (FISH) with probes specific for the translocated and centric segments of chromosome 22. An initial cycle was unsuccessful, producing 11 embryos for biopsy, only one of which, when followed up on day 4, yielded more than 10 nuclei (median 7.5, n=10). In addition, five of the embryos showed mosaic or chaotic chromosome constitutions; some of these embryos had fragmented or multilobed abnormal nuclei, hindering interpretation of the FISH signals. The single embryo transferred did not result in a pregnancy. A second cycle, using a revised protocol, produced 10 embryos, three of which were transferred, resulting in an ongoing singleton pregnancy. All the remaining embryos yielded 12 to 23 nuclei by day 4 (median 17, n=7). Apart from some tetraploid nuclei, only one embryo showed mosaicism. The significance of the changes in protocol leading to the successful outcome is discussed, and the pattern of meiotic segregation products is analysed and compared with other previous reports of reciprocal translocations.

Human embryos derived from in vitro and in vivo matured oocytes: analysis for chromosomal abnormalities and nuclear morphology

PURPOSE

To determine whether embryos resulting from oocytes matured in vitro have a higher incidence of nuclear and/or genetic abnormalities compared to embryos resulting from oocytes matured in vivo.

METHODS

Fluorescence in situ hybridization analysis for chromosomes X, Y, and 18 was used to compare the rates of aneuploidy, mosaicism, and nuclear abnormalities in embryos derived from oocytes that were prophase I at aspiration (immature group) to that observed in embryos resulting from oocytes that were metaphase I or II at aspiration (mature group).

RESULTS

Based on nuclear morphology, significantly more embryos in the mature group (23%) were classified as normal compared to embryos in the immature group (3%). No difference was found in the rate of aneuploidy or in the incidence of mosaicism involving these chromosomes.

CONCLUSIONS

These findings suggest that few embryos derived from prophase I oocytes collected following ovarian stimulation are morphologically normal.

The probability of abnormal preimplantation development can be predicted by a single static observation on pronuclear stage morphology

This retrospective study was undertaken to determine whether further developmental progression of two-pronucleated (2PN) zygotes can be predicted by a single, non-invasive examination of pronuclei, with the use of criteria based on the number and distribution of nucleolar precursor bodies in each pronucleus. The normal range of pronuclear variability was defined by analysis of zygotes giving rise to embryos transferred in 100%-implantation cycles (pattern 0). Morphological patterns differing from pattern 0 were classified as patterns 1-5. The frequency of developmental arrest of pattern 0 zygotes was only 8.5% as compared with 31.6, 21.9, 30.0, 20.5 and 24. 1% for patterns 1-5 respectively. Relationships of pronuclear patterns with blastomere multinucleation and cleaving embryo morphology were also noted. Clinical pregnancy was achieved in 22 of 44 (50%) treatment cycles in which at least one pattern 0 embryo was transferred, but only in two of 23 (9%) cycles in which only pattern 1-5 embryos were transferred. These data present new evaluation criteria which can be used to predict the developmental fate of human embryos as early as the pronuclear stage, without requiring repeated observations or an exact timing of pronuclear zygote inspection. Further prospective study is needed for clinical validation of these criteria.

Preimplantation diagnosis by fluorescence in situ hybridization using 13-, 16-, 18-, 21-, 22-, X-, and Y-chromosome probes

PURPOSE

Our purpose was to select the proper chromosomes for preimplantation diagnosis based on aneuploidy distribution in abortuses and to carry out a feasibility study of preimplantation diagnosis for embryos using multiple-probe fluorescence in situ hybridization (FISH) on the selected chromosomes of biopsied blastomeres.

METHODS

After determining the frequency distribution of aneuploidy found in abortuses, seven chromosomes were selected for FISH probes. Blastomeres were obtained from 33 abnormal or excess embryos. The chromosome complements of both the biopsied blastomeres and the remaining sibling blastomeres in each embryo were determined by FISH and compared to evaluate their preimplantation diagnostic potential.

RESULTS

Chromosomes (16, 22, X, Y) and (13, 18, 21) were selected on the basis of the high aneuploid prevalence in abortuses for the former group and the presence of trisomy in the newborn for the latter. Thirty-six (72%) of 50 blastomeres gave signals to permit a diagnosis. Diagnoses made from biopsied blastomeres were consistent with the diagnoses made from the remaining sibling blastomeres in 18 embryos. In only 2 of 20 cases did the biopsied blastomere diagnosis and the embryo diagnosis not match.

CONCLUSIONS

If FISH of biopsied blastomere was successful, a preimplantation diagnosis could be made with 10% error. When a combination of chromosome-13, -16, -18, -21, -22, -X, and -Y probes was used, up to 65% of the embryos destined to be aborted could be detected.

[Monozygotic pregnancy after the treatment for infertility by transfer of frozen-thawed embryos]

OBJECTIVES

It has been suggested that monozygotic pregnancies occur more frequently after in vitro fertilisation. This phenomenon is attributed to a number of factors including in vitro culture conditions, malformation of the zona pellucida due to manipulation on the oocytes and artificial opening of the zona pellucida.

DESIGN

Retrospective analysis of monozygotic pregnancies in an IVF-ET procedures and obstetrical these pregnancies outcome.

MATERIALS AND METHODS

A total of 2254 IVF-ET procedures were analysed. Three protocols were used for ovarian stimulation: short or long protocols with gonadotropins releasing hormone analogue or clomiphene citrate with hMG. In 811 cases male factor was diagnosed and intracitoplasmatic sperm injections were performed.

RESULTS

549 clinical pregnancies were achieved in analysed group. In six cases ultrasound examination 5 weeks after embryo transfer showed a greater number of foetus than the number of embryo transferred. In three of those cases the embryos were obtained after ICSI. Age and average thickness of zona pellucida were similar in group of patients with monozygotic pregnancies when compared with all pregnant patients after IVF treatment.

CONCLUSIONS

The incidence of monozygotic pregnancy is increased in group pregnancies resulting from IVF ET. No single risk factor can explain this phenomena. This type of pregnancy needs special obstetrical attention.

Laser scanning confocal imaging of abnormal or arrested human preimplantation embryos

PURPOSE

The improved resolution and optical sectioning of a confocal microscope make it an ideal instrument for extracting three-dimensional information, especially from extended biological specimens such as human embryos. The staining of actin together with chromatin allowed us to specify the architecture of the embryo and the appearance of the nucleus.

METHODS

F-Actin and chromatin distributions were visualized using laser scanning confocal microscopy in "fresh" and "cryopreserved" human preimplantation embryos obtained by in vitro fertilization.

RESULTS

The current study revealed a high rate of multinucleation in arrested or poor-quality embryos (89%, in grade IV embryos).

CONCLUSIONS

Confocal microscopy revealed high levels of multinucleated blastomeres, suggesting that the probable cause of arrested development in these embryos was due to multinucleation of blastomeres.

Preimplantation diagnosis by FISH: the Rambam experience

PURPOSE

Our purpose was to summarize our experience gained using fluorescence in situ hybridization for preimplantation diagnosis at the Rambam Medical Center.

METHODS

Seventy-three embryos (29 cycles) were analyzed for preimplantation diagnosis for the following indications: advanced maternal age (> 39 years), X-linked diseases, poor-quality embryos, repeated failure in vitro fertilization cycles and fast-dividing embryos. An additional 38 embryos with unequal pronuclei size were examined for ploidy. Biopsy of embryonic blastomeres was performed at the six- to eight-cell stage. Five fluorescence probes, for chromosomes X, Y, 13, 18, and 21, were applied for ploidy detection.

RESULTS

Eighty-four (87%) blastomeres of the 73 embryos analyzed showed clear signals. Six of the blastomeres were lost during spreading. Two of the embryos were destroyed following biopsy. No nucleus was found in five of the blastomeres, while in nine, more than one nucleus was verified. Transfer was performed in 10 patients (32 embryos). Two pregnancies were achieved. Two healthy babies were born. Fifty-seven percent of the fast-dividing embryos demonstrated normal signals. In two groups of embryos of unequal pronuclei size following conventional insemination and intracytoplasmic sperm injection, 50 and 11.4% demonstrated normal signals.

CONCLUSIONS

The efficiency of fluorescence in situ hybridization for aneuploidy detection is 87 and 97% for autosomes and gonosomes, respectively. The preimplantation genetic diagnosis is suitable for selected in vitro fertilization cases including fast-dividing embryos and embryos with unequal pronuclei size following regular in vitro fertilization.

Simultaneous detection of chromosomes X, Y, 13, 18, and 21 by fluorescence in situ hybridization in blastomeres obtained from preimplantation embryos

PURPOSE

Simultaneous fluorescence in situ hybridization (FISH) was used in a preimplantation genetic diagnosis program to determine which embryos were normal for chromosomes X, Y, 13, 18, and 21.

METHODS

Single blastomeres were disrupted and attached to glass slides using acetic acid and ethanol. Using a ratio mixture of chromosome enumeration DNA probes in combination with locus-specific identifier DNA probes, FISH was performed for the identification of chromosomes X, Y, 13, 18, and 21.

RESULTS

Fourteen couples enrolled in IVF produced 134 embryos for biopsy. Blastomeres subjected to five-color FISH revealed that 22% of embryos were normal for chromosomes X, Y, 13, 18, and 21. In addition, 52% were abnormal and no results could be detected for 25%. Twelve couples underwent embryo transfer, two couples did not receive embryos due to lack of any normal embryos, and three couples became pregnant.

CONCLUSIONS

The simultaneous detection of five-color FISH is a feasible method to detect aneuploidy in preimplantation embryos from women of advanced maternal age.

Infertile couples with Robertsonian translocations: preimplantation genetic analysis of embryos reveals chaotic cleavage divisions

Preimplantation genetic diagnosis (PGD) may provide a feasible option for some Robertsonian translocation carriers who experience severe difficulty in achieving a normal pregnancy. We report on five PGD cycles for two such couples, 45,XY,der(13;14)(q10:q10) and 45,XX,der(13;21)(q10;q10), carried out by biopsy of two cells from day 3 post-insemination embryos generated by in vitro fertilisation. Locus-specific YAC probes for chromosomes 13, 14 and 21 were used to detect the chromosomes involved in the translocation using multicolour FISH. Three embryos transfers were carried out (two single embryo transfers and one double transfer) but no clinical pregnancies were established. In two cycles no embryos were transferred as all those biopsied were chromosomally abnormal. Combined results from both couples show 13% (6/45) of embryos analysed were normal for the translocation chromosomes and 87% (39/45) were chromosomally abnormal; these were categorised as 36% aneuploid or aneuploid mosaic and 51% chaotic where the chromosome constitution varied randomly from cell to cell. This suggests two factors may be acting to reduce fertility in these couples; the aneuploid segregation of the parental Robertsonian translocation and also a post-zygotic factor leading to uncontrolled chromosome distribution in early cleavage stages in an exceptionally high proportion of embryos.

Clinical application of preimplantation diagnosis for myotonic dystrophy

Myotonic dystrophy (DM) or Steinert's disease is a progressive autosomal dominant disease characterized by increasing muscle weakness, myotonia, cataracts, and endocrine abnormalities such as diabetes and testicular atrophy. The gene for DM was cloned in 1992 and the mutation was shown to be an expanded trinucleotide (CTG) repeat. A polymerase chain reaction (PCR)-based assay was described soon after that would allow (prenatal) diagnosis of the disease. Based on these PCR assays, we have developed a method for carrying out single-cell PCR for DM. In preimplantation diagnosis, embryos obtained in vitro are checked for the presence or absence of a disease, after which only embryos shown to be free of the disease under consideration are returned to the mother. A single-cell assay was developed for preimplantation diagnosis in couples where one of the parents is afflicted with DM. Twenty intracytoplasmic sperm injection (ICSI) cycles were carried out in eight patients and between one and four embryos were replaced in 17 out of 20 cycles. Two of the patients became pregnant and have had prenatal diagnosis which has confirmed that they are unaffected.

Preimplantation development of mouse and human embryos biopsied at cleavage stages using a modified displacement technique

A modified embryo biopsy method was tested on four- and eight-cell stage mouse embryos and used on human embryos to obtain blastomeres for preimplantation genetic diagnosis. The biopsy method tested combines zona drilling and fluid displacement to force one or two cells through an opening in the zona pellucida of the cleavage-stage embryo. Rates of cell division and the percentage of mouse embryos forming blastocysts following biopsy at the eight-cell stage were not significantly different from those observed in unoperated control embryos. The percentage blastocyst formation was not significantly different in embryos biopsied at the four-cell stage and in control embryos, although cell division was significantly retarded following biopsy. 96% of the mouse blastomeres isolated at the eight-cell stage were recovered intact and 96% of those placed in culture underwent cell division. Survival and division of cells isolated at the four-cell stage were 92 and 84% respectively. Most of the cultured blastomeres cleaved several times and formed small trophoblast vesicles. Chromosomes were observed in 59% of blastomeres incubated in the presence of colcemid. In the initial use of this biopsy technique for human preimplantation genetic diagnosis, blastocyst formation was observed in 9 of 13 human embryos biopsied at the 7- to 10-cell stage. These findings support the use of this biopsy method as an alternative to aspiration techniques.

The presence of multinucleated blastomeres in human embryos is correlated with chromosomal abnormalities

The purpose of the present study was to determine whether the presence of one or more multinucleated blastomeres during early embryonic development is associated with chromosomal abnormalities in sibling blastomeres of that embryo. Embryos with multinucleated cells (n = 47) detected on day 2 or 3 or development were compared to dividing embryos without multinucleation. Arrested embryos were excluded from this study. Chromosome abnormalities were detected using fluorescent in-situ hybridization (FISH) with X, Y, 18 and 13/21 chromosome-specific probes. Of 47 embryos included in this study, 76.6% were chromosomally abnormal, compared to 50.9% in the control group (P < 0.001). Excluding aneuploidy, which is originated in the gametes and not the embryo, the differences were even higher, with 74.5% of multinucleated embryos being chromosomally abnormal compared to 32.3% of non-multinucleated embryos (P < 0.001). Day of multinucleation appearance, number of nuclei per cell, number of multinucleated cells per embryo and developmental quality of the embryos as well as the type of fertilization (intracytoplasmic sperm injection versus standard insemination) were not found to affect the rate of chromosomal abnormalities in embryos with multinucleated cells. These results suggest that embryos with multinucleated cells may not be suitable for replacement and should be excluded unless no other embryos are available.

Review: preimplantation diagnosis of inherited disease

Preimplantation diagnosis of inherited diseases has become possible with the techniques of in vitro fertilization, blastomere biopsy of the 6- to 10-cell embryo and DNA analysis of the single blastomeres. Disease-free embryos are selected for transfer to the uterus, thereby avoiding the need for termination of a fetus diagnosed as affected in prenatal diagnosis in the first or early-second trimester of pregnancy. The genetic indications for preimplantation diagnosis are theoretically the same as for prenatal diagnosis, but the defects must be detectable by the polymerase chain reaction. For X-linked recessive diseases, fluorescence in situ hybridization can be used as an alternative for the selection of female embryos. So far almost 40 healthy children have been born worldwide after preimplantation diagnosis for genetic disease. The possibilities and limitations of preimplantation diagnosis, especially in prevention of inherited disease, are discussed in this review.

Management of rhesus isoimmunization by preimplantation genetic diagnosis

A genetic assay by single blastomere analysis was developed for rhesus (RhD) blood group typing of early cleavage stage embryos. The method, which is based on the simultaneous amplification of an RhD-specific sequence and an internal control in single cells, was applied for the selective transfer of RhD-negative embryos in a family of an RhD sensitized woman and a heterozygote partner. The RhD status of two out of three biopsied embryos was determined. According to their amplified products, both were typed as RhD-negative and transferred to the uterus. Pregnancy was not achieved.