Somatic homologous recombination in plants is promoted by a geminivirus in a tissue-selective manner

Four transgenic Arabidopsis thaliana lines carrying different reporter gene constructs based on split glucuronidase genes were used to monitor the frequency of somatic homologous recombination after geminivirus infections. Euphorbia mosaic virus and Cleome leaf crumple virus were chosen as examples, because they induce only mild symptoms and are expected to induce less general stress responses than other geminiviruses. After comparing the different plant lines and viruses as well as optimizing the infection procedure, Euphorbia mosaic virus enhanced recombination rates significantly in the transgenic reporter line 1445. The effect was tissue-specific in cells of the leaf veins as expected for this phloem-limited virus. The advantage for geminiviruses to activate a general recombination pathway is discussed with reference to an increased fitness by generating virus recombinants which have been observed frequently as an epidemiologic driving force.

Selection for faster development does not bias sex ratios resulting from blastocyst embryo transfer

Concerns of possible male biased sex ratios with IVF exist due to reports of faster preimplantation development for male relative to female embryos in a variety of mammals, including humans. This study reports the first direct test of the hypothesis that selection for faster preimplantation development to the blastocyst stage increases the likelihood of a male birth. Gender outcomes of all live births resulting from blastocyst stage embryo transfer within a large assisted reproduction practice were reviewed, along with associated embryological records. The developmental stage of transferred embryos relative to the average developmental stage of all viable embryos in each cohort was related to gender outcomes by logistic regression analysis. Gender data were available for 1,184 children born from 815 pregnancies resulting from blastocyst stage embryo transfer during the study period. Data on preimplantation embryonic development were available for 737 cycles resulting in the birth of 1,075 children. There was no relationship between selection for developmental rate and the gender of resulting children. Numbers of male and female children were nearly identical within this patient population (593 male versus 591 female). These results indicate that offspring gender is unrelated to selection for developmental rate among blastocyst transfer cycles.

Preimplantation genetic diagnosis and screening

Preimplantation genetic diagnosis (PGD) identifies genetic abnormalities in preimplantation embryos prior to embryo transfer. PGD is an exciting technology that may improve the likelihood of a successful pregnancy and birth for five distinct patient groups: (1) those with infertility related to recurrent miscarriages or unsuccessful in vitro fertilization (IVF) cycles, (2) those with unexplained infertility, (3) advanced maternal age, (4) severe male factor infertility, and (5) couples at risk for transmitting a hereditary disease to their offspring. PGD is always performed following an IVF cycle where multiple oocytes are retrieved and fertilized. Sophisticated techniques such as multiprobe, multicolor fluorescence in situ hybridization are used to test single cells for structural or numerical chromosome abnormalities, whereas the polymerase chain reaction, linkage analysis, and DNA sequencing are used to analyze single cells for disease-specific DNA mutations. PGD allows one to transfer only those embryos identified as being free of genetic abnormalities, thus potentially increasing the implantation rate and decreasing the miscarriage rate. These technologies identify embryos free of specific genetic abnormalities and may increase the likelihood of achieving the patient's goal: the birth of a healthy infant.

Quantitative grading of a human blastocyst: optimal inner cell mass size and shape

OBJECTIVE

To investigate the predictive value of quantitative measurements of blastocyst morphology on subsequent implantation rates after transfer.

DESIGN

Prospective observational study.

SETTING

Private assisted reproductive technology center.

PATIENT(S)

One hundred seventy-four IVF patients receiving transfers of expanded blastocyst-stage embryos on day 5 (n = 112) or day 6 (n = 62) after oocyte retrieval.

INTERVENTION(S)

None.

MAIN OUTCOME MEASURE(S)

Blastocyst diameter, number of trophectoderm cells, inner cell mass (ICM) size, ICM shape, and implantation and pregnancy rates.

RESULT(S)

Blastocyst diameter and trophectoderm cell numbers were unrelated to implantation rates. Day 5 expanded blastocysts with ICMs of >4,500 microm(2) implanted at a higher rate than did those with smaller ICMs (55% vs. 31%). Day 5 expanded blastocysts with slightly oval ICMs implanted at a higher rate (58%) compared with those with either rounder ICMs (7%) or more elongated ICMs (33%). Implantation rates were highest (71%) for embryos with both optimal ICM size and shape. Pregnancy rates were higher for day 5 transfers of optimally shaped ICMs compared with day 5 transfers of optimally sized ICMs.

CONCLUSION(S)

Quantitative measurements of the inner cell mass are highly indicative of blastocyst implantation potential. Blastocysts with relatively large and/or slightly oval ICMs are more likely to implant than other blastocysts.

Dramatic declines in implantation and pregnancy rates in patients who undergo repeated cycles of in vitro fertilization with blastocyst transfer after one or more failed attempts

OBJECTIVE

To compare the outcome of second and third cycles of in vitro fertilization with blastocyst transfer to the outcome of first attempts at IVF with blastocyst transfer.

DESIGN

Retrospective study.

SETTING

Private ART center.

PATIENT(S)

Three hundred and four patients undergoing treatment with in vitro fertilization with blastocyst transfer, 87 of which underwent at least one cycle of re-treatment after failing to achieve pregnancy in their first cycle.

INTERVENTION(S)

Bipronucleate oocytes were grown for up to 144 hours and subsequently transferred when at least one embryo attained the expanded blastocyst stage.

MAIN OUTCOME MEASURE(S)

Pregnancy and implantation rates.

RESULT(S)

Pregnancy rates per retrieval were significantly higher for patients undergoing their first cycle of in vitro fertilization with blastocyst transfer (36%) compared to those undergoing their second (19%) or their third (9%) cycles of treatment. Implantation rates per embryo were also higher for first cycles of in vitro fertilization with blastocyst transfer (30%) compared to second (18%) or third cycles (8%).

CONCLUSION(S)

Pregnancy and implantation rates decline dramatically in repeated cycles of in vitro fertilization with blastocyst transfer following one or more unsuccessful cycles of in vitro fertilization with blastocyst transfer.

A comparison of day 5 and day 6 blastocyst transfers

OBJECTIVE

To compare implantation and pregnancy rates according to the day of embryo transfer (day 5 or 6 after oocyte retrieval) when transfer was postponed until expanded blastocysts developed.

DESIGN

Retrospective clinical study.

SETTING

Private ART center.

PATIENT(S)

One-hundred and eighty-three women undergoing blastocyst-stage embryo transfer following in vitro fertilization.

INTERVENTION(S)

Bipronucleate oocytes were grown for up to 144 hours and subsequently transferred only when at least one embryo attained the expanded blastocyst stage.

MAIN OUTCOME MEASURE(S)

Implantation and pregnancy rates.

RESULT(S)

Blastocysts transferred on day 5 implanted at nearly twice the rate of blastocysts transferred on day 6 (36.3% vs. 19.0%). Pregnancy rates were also almost twice as high among the day 5 transfer patients (59.3% vs. 32.3%). In addition, more blastocysts developed (3.6 vs. 2.4), and more were transferred (2.7 vs. 2.3) to the day 5 transfer patients, although the proportion of expanded blastocysts among the blastocysts that were transferred was the same for the two groups (91.7% vs. 93.6%).

CONCLUSION(S)

Embryos that develop to the expanded blastocyst stage and are transferred on day 5 after retrieval are approximately twice as likely to implant compared to those for which expansion and transfer are delayed until day 6.

Predictive value of 72-hour blastomere cell number on blastocyst development and success of subsequent transfer based on the degree of blastocyst development

OBJECTIVE

To determine the predictive value of 72-hour blastomere cell number on blastocyst development and to compare success rates of subsequent transfer based on the degree of blastocyst development.

DESIGN

Retrospective clinical study.

SETTING

Private assisted reproductive technology center.

PATIENT(S)

Ninety-three women aged 32.0 +/- 5.1 years undergoing oocyte retrieval for IVF.

INTERVENTION(S)

Bipronucleate oocytes obtained from IVF were grown for up to 168 hours after fertilization and subsequently transferred at the blastocyst stage.

MAIN OUTCOME MEASURE(S)

Percentages of embryos developing to blastocyst from 72-hour embryos by blastomere cell number and subsequent implantation and pregnancy rates of transferred blastocysts.

RESULT(S)

Rates of blastocyst formation and expansion increased as cell numbers at 72 hours increased. Implantation rates were 43% for embryos transferred to women receiving only expanded blastocysts and 17% for embryos transferred to women receiving one or more less developed blastocysts. Pregnancy rates were higher for women receiving only expanded blastocysts than for women receiving one or more less developed blastocysts, although the difference was not significant.

CONCLUSION(S)

More developed 72-hour embryos are more likely to become blastocysts and expand. Implantation rates are greater for the transfer of expanded rather than unexpanded blastocysts.