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3. Egg and Embryo Factorsto "Why does IVF fail?" main page IVF tells us a lot about a patient’s egg and embryo quality. Other
pages on our web site review the assessment of eggs and embryos in the IVF
lab. There is no other a. Number of eggsMany patients feel disappointed when the number of eggs obtained at egg retrieval are less than expected based upon the ultrasound exam done on the day of HCG. Quality is what really counts. On one end of the spectrum are the patients that produce excessive numbers of eggs (i.e., PCOS) yet many may not have great fertilization or embryo quality. In fact, there is a movement now to do more gentle stimulations, which may give us better quality and lower the risk of OHSS. It patients known to be hyper responders from previous stimulations, the long Lupron protocol with BCPS and only 150 IU of FSH has been shown to produce good results. Some patients produce few eggs, however. They may be older, have higher day #3 FSH levels, or have had severe endometriosis involving the ovaries. In spite of ‘normal’ day 3 FSH levels, some feel that retrieval of few eggs represents diminished ovarian reserve. Obviously, switching to a short ‘micro Lupron’ protocol may improve the stimulation. Addition of DHEA may also improve the stimulation. Still, we have had many patients conceive with a single embryo transfer and it is the embryo quality seems to be more important the numbers. There are various definitions of ‘poor responders’ including requiring > 3000 IU FSH to stimulate the ovaries for a cycle, a day 5 of medications estradiol level of less than 100 pg/ml or 75 pg/ml, a peak estradiol at the time of HCG of < 300 pg/ml or fewer than 3 eggs retrieved. b. Embryo FragmentationTo some degree the majority of embryos have some fragmentation in IVF.
There are different grading systems in use that indicate the amount of
fragmentation. In general, the greater the degree of fragmentation the
lower the pregnancy rates though this is not an absolute. The use of a
scoring system that uses fragmentation as well as blastomere numbers in
the embryo helps to assess the potential health and viability of the
embryos and the chances for success. Other pages on our site show the
reader what fragmentation looks like. c. Embryo growth rateIn addition to fragmentation, the number of blastomeres in each embryo is assessed at defined intervals after fertilization has occurred. In general, on the day after the eggs and sperm are united we see the zygote or occasionally a two-cell embryo. The zygote is the fertilized egg with 2 pronuclei representing the chromosomes from maternal and paternal individuals. The orientation and composition of the pronuclei may have a bearing on the eventual pregnancy rates and have been used as markers. At roughly 48 hours post-insemination we see embryos that are in the 3-5 cell range and at 72 hours embryos in the 6-8 cell range. On day 4 post-insemination we may see the morula or early blastocyst and on day 5 the more expanded blastocyst. There is of course differences in the rate at which embryos develop and to some degree slow growing or to fast growing embryos may be more likely abnormal with respect to chromosome complements. When there are a large number of eggs this may not be as important as when there are only a few eggs/embryos to choose to transfer. Many IVF programs have norms they typically see and can determine if a given patient falls out of these norms d. Immature eggs at retrievalThe mature oocyte is termed metaphase II (MII) oocyte and it is fully capable to be fertilized. Photos of oocytes are on other pages of our site. The immature stages include the metaphase I oocyte and the germinal vesicle stage oocyte. During the process of ovarian stimulation it is unusual to have all of the oocytes collected at the MII stage. This likely represents the fact that we retrieve oocytes from as many follicles, large and small, as we can. Immature oocytes many come from the smaller follicles. If there are only a few immature oocytes overall it may not be an issue. However, on rare occasions all the oocytes are immature. We can check the serum HCG level to see if the medication was administered correctly. Attempts have been made to mature the oocytes in vitro and then perform ICSI with success. Some studies show lower pregnancy rates compared to fertilization of fresh MII oocytes and some show a lower pregnancy rate. It is an option. The lower pregnancy rate in some studies could be due to abnormalities of the spindle apparatus and chromosome segregation during the culture process. Another option is to stimulate the patient with different medications and a different protocol. e. Fractured Zona PellucidaThe zona pellucida is the shell about the oocyte and embryo. We occasionally see broken zonas (Figure 8) at the when the oocyte is examined at the time of ICSI or at the time of fertilization. This appear to occur with about 5% of all oocytes collected. Figure 8. Intact zona pellucida with fertilized oocyte
In the past, it was thought that excessive aspiration pressure generated by a syringe aspiration system was responsible. These days, most programs use an aspiration pump which is more gentle and generates appropriate pressure. Still, we may see this phenomenon. It may be associated with cycles where the estradiol levels are high in the days before HCG administration (i.e. mild OHSS) as many of these oocytes with fractured zonas are from cycles with high numbers of eggs collected. The pregnancy rates are the same in cycles where only intact zonas are seen. Over-maturation of the oocyte with atresia may be the basis. f. PolyspermyPolyspermy refers to the fertilization of the oocyte by more than one
sperm. Examination of the egg about 16-18 hours past insemination shows
the presence of more than 2 pronuclei in the center of the cell (See Fig.
8). This suggests that the mechanisms to prevent ore than one sperm from
entering (i.e. cortical granule release, change in membrane charge) have
failed. It may be seen when these are very high concentrations of sperm in
the insemination media, oocytes that are immature or post mature,
different timing of the insemination relative to HCG administration, pH or
protein media, abnormal ZP-1 or ZP-3, proteins in the zona pellucida
involved with sperm and oocyte binding. It is not related to the age of
the patient or the method of insemination. This underscores the importance
of examining the oocytes at the appropriate time, and these embryos may
develop normally, yet have 69 or 92 chromosomes rather than 46 if 1 or 2
extra sperm penetrate the egg. |
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