A Case for Transferring Blastocysts on Day 5-6 Post-Fertilization Rather Than on Day 2-3 as Cleaved Embryos.

Embryo transfer (ET) is undoubtedly the single most important step in IVF. It takes confidence, dexterity, skill and timing to optimally perform ET. Of all the procedures conducted in IVF, embryo transfer is the most difficult to perfect. Sadly, far too many women fail to conceive simply because of poor timing and technique of ET.

While the debate over whether it is better to transfer cleaved embryos (day 2-3 post-fertilization) rather than blastocysts (day 5-6) continues to rage, an ever-growing percentage of IVF practitioners are reaching the realization that it is more beneficial to transfer blastocysts than cleaved embryos and here is why:

Cleaved embryos (day 2-3, post-fertilization) that fail to develop in culture to blastocysts by day 5-6 post-fertilization are almost invariably “incompetent” such that had they been transferred earlier they would not have propagated a pregnancy anyway. While in about 70% of such cases, this arrest in embryo development is due to numerical chromosomal aberrations (aneuploid) it can also be due to genetic or metabolic abnormalities, most of which are presently undiagnosable in advance. 

There would have been no benefit in transferring such cleaved embryos because they would not have developed into blastocysts in the uterus anyway. Simply stated, there appears to be absolutely no validity to the assertion that an embryo would develop better and have a greater chance of propagating a baby in inside the uterus earlier than it would by being allowed to first develop into a blastocyst in an incubator.

A recent publication suggested that embryos that require 7 days (rather than 5-6) to reach the blastocyst stage of development are capable of developing into healthy concepti. In my experience this is not accurate. We have transferred many such day 7 blastocysts, and none have propagated viable pregnancies. Accordingly, I am not a proponent of transferring such late blastocysts.

Transferring expanded blastocysts allows for the transfer of fewer embryos and minimizes the risk of multiple pregnancies with its incumbent risks. The reason is that each embryo that develops into an expanded blastocyst by day 5-6 post fertilization has a much greater chance of implanting and propagating a viable baby than does the transfer of a cleaved (day 2-3) embryo. a cleaved embryo. While this differential in baby rate per embryo is affected by the age of the egg provider, it occurs in every female age category.  So, by waiting to day 5-6, many the selective transfer of fewer embryos will produce the optimal success.

The advent of preimplantation genetic testing (PGT) has heralded the era where we can further improve the assessment of embryo competency, by identifying euploid embryos that have a normal numerical chromosomal configuration (karyotype), thereby further improving the baby rate per transferred embryo. The fact that optimal PGT analysis relies on chromosomal analysis of cells biopsied from blastocysts, further highlights the advantage in growing embryos to the blastocyst stage.

Don’t get me wrong! I am not saying that there is absolutely no place for transferring cleaved embryos. I say this because taking an embryo to blastocysts does absolutely nothing to improve its implantation potential. It is simply a selection process because of the culling effect achieved by growing it for 2-3 days longer (see above). Simply stated, an embryo that is destined to propagate a baby will just as readily do so whether it is transferred cleaved or as an expanded blastocyst. It is just that we can’t identify “competent” embryos without challenging them by allowing them 5-6 days to try and reach the blastocyst stage of development.

We know that >80% of euploid day 3 embryos subsequently develop into expanded blastocysts (regardless of the age of the egg provider). By comparison, untested embryos (where it is not known whether the embryo is aneuploid or euploid) have at best, a 30- 40% of developing into blastocysts.

The only scenario where the transfer of cleaved embryos might be preferential, is where the patient only has 1-2 cleaved embryos in total by day 3, post-fertilization. In such cases it is often pointless delaying 5-6 days before ET. Earlier transfer will save the woman having to wait 2 additional days before undergoing ET. 

The following are strong arguments in favor of blastocysts transfers:

  1. Diagnostic Advantages:
    1. Since aside from the woman’s age, the protocol used for of ovarian stimulation also impacts egg development and “competency” it follows that knowledge of how many fertilized, mature (MII) eggs develop into blastocysts will play a role in selecting a future approach to ovarian stimulation
    2. The growing popularity of Single Blastocyst Transfers (SBT) to virtually eliminate the danger of multiple pregnancies, requires as much information regarding embryo “competency” as possible. The proven ability of an embryo to reach the blastocysts stage, helps considerably in this regard.

Of course, for the treating physician it is far less stressful not have to have to confront a patient with their having no surviving embryos to transfer. Undoubtedly, this is one of the main reasons why IVF practitioners often, erroneously prefer to transfer cleaved embryos rather than blastocysts. But as far as I am concerned, this is not in the in best interest of the patients. It is in my opinion, far better to advise the patient to opt for a blastocyst transfer.



Dear, is there a way to improve the rate of day 5 embryo’s? In my first ivf cycle I had 4 embryo’s looking great on day 3, but only one made it to day 5.

Dr. Geoffrey Sher

In most cases, this is the consequence of the protocol used for ovarian stimulation and its implementation , often aggravated by the adverse effect on egg “competency, of advancing age and diminishing ovarian reserve.

The importance of the IVF stimulation protocol on egg/embryo quality cannot be overstated. This factor seems often to be overlooked or discounted by t IVF practitioners who use a “one-size-fits-all” approach to ovarian stimulation. My experience is that the use of individualized/customized COS protocols can greatly improve IVF outcome. While no one can influence underlying genetics or turn back the clock on a woman’s age, any competent IVF specialist should be able to tailor the protocol for COS to meet the individual needs of the patient.
Gonadotropins (LH and FSH), whether produced by the pituitary gland or administered by way of fertility drugs, have different “targeted” sites of action in the ovary. FSH targets cells that line the inner wall of the follicle (granulosa cells) and also form the cumulus cells that bind the egg to the inner surface of the follicle. Granulosa cells are responsible for estrogen production.
LH, on the other hand, targets the ovarian connective tissue (stroma/theca) that surrounds ovarian follicles resulting in the production of male hormones such as testosterone (predominantly), androstenedione and DHEA. These androgens are then transported to the granulosa cells of the adjacent follicles in a “bucket brigade fashion”. There FSH converts testosterone to estradiol, causing granulosa cells to multiply (proliferate) and produce estradiol, follicles to grows and eggs to develop (ovogenesis) It follows that ovarian androgens (mainly testosterone) is absolutely indispensable to follicle/ egg growth and development.
However, the emphasis is on a “normal” amount of testosterone. Over-exposure of the follicle to testosterone can in my opinion, compromise egg development and lead to an increased likelihood of chromosomal irregularities (aneuploid) following LH/hCG-induced egg maturational division (meiosis) and compromise embryo “competency/quality.
Ovarian androgens can also reach the uterine lining where they sometimes will compromise estrogen receptor -induced endometrial growth and development.
A significant percentage of older women and those who have diminished ovarian reserve (DOR) have increased LH activity is increased. Such women either over-produce LH and/or the LH produced is far more biologically active. Chronically increased LH activity leads to overgrowth of ovarian connective tissue (stroma/theca). This condition, which is often referred to as Stromal Hyperplasia or hyperthecosis can result in excessive ovarian androgen/testosterone production and poorer egg-embryo quality/competency, Similarly, women with polycystic ovarian syndrome (PCOS), also characteristically have Stromal hyperplasia/hyperthecosis due to chronically increased LH activity. Thus they too often manifest with increased ovarian androgen production. It is therefore not surprising that “poor egg/embryo quality” is often also a feature of PCOS.
In my opinion, the over-administration of LH-containing menotropins such as Menopur, [which is comprised of roughly equal amount of FSH and hCG ,which acts similar to LH)], to older women, women with DOR and those who have PCOS can also lead to reduced egg/embryo competency . Similarly, drugs such as clomiphene or Letrozole that cause the pituitary gland to release excessive amounts of LH, are also potentially harmful to egg development and in my opinion, are best omitted from IVF COS protocols. This is especially the case when it comes to older women and those with DOR, who in my opinion should preferably be stimulated using FSH-dominant products such as Follistim, Puregon, Fostimon and Gonal-F.
Gonadotropin releasing hormone agonists (GnRHa): GnRHa such as Lupron, Buserelin, Superfact, Gonopeptyl etc. are often used to launch ovarian stimulation cycles. They act by causing an initial outpouring followed by a depletion of pituitary gonadotropins. This results in LH levels falling to low concentrations, within 4-7 days, thereby establishing a relatively “LH-free environment”. When GnRHa are administered for about 7 days prior to initiating gonadotropin stimulation (“long” pituitary down-regulation”), the LH depletion that will exist when COS is initiated, will usually be protective of subsequent egg development. In contrast, when the GnRHa administration commences along with the initiation of gonadotropin therapy, there will be a resultant immediate surge in the release of pituitary LH with the potential to increase ovarian testosterone to egg-compromising levels , from the outset of COS. This, in my opinion could be particularly harmful when undertaken in older women and those who have DOR.
GnRH-antagonists such as Ganirelix, Cetrotide and Orgalutron, on the other hand, act very rapidly (within hours) to block pituitary LH release. The purpose in using GnRH antagonists is to prevent the release of LH during COS. In contrast, the LH-lowering effect of GnRH agonists develops over a number of days.
GnRH antagonists are traditionally given, starting after 5th -7th day of gonadotropin stimulation. However, when this is done in older women and those (regardless of age) who have DOR, LH-suppression might be reached too late to prevent the deleterious effect of excessive ovarian androgen production on egg development in the early stage of ovarian stimulation. This is why, it is my preference to administer GnRH-antagonists, starting at the initiation of gonadotropin administration.
My preferred Protocols for Controlled Ovarian Stimulation (COS):
1. “Long” GnRHa (Lupron/Buserelin/Superfact/Gonopeptyl) Pituitary Down-regulation Protocol: The most commonly prescribed protocol for GnRHa/gonadotropin administration is the so-called “long protocol”. Here, GnRHa is given, starting a week or so prior to menstruation. This results in an initial rise in FSH and LH , which is rapidly followed by a precipitous fall to near zero. It is followed by a withdrawal bleed (menstruation), whereupon gonadotropin treatment should commence, while daily Lupron injections continue, to ensure a “low LH” environment. A modification to the “long protocol” which I prefer prescribing for older women and in cases of DOR, is the Agonist/Antagonist Conversion Protocol (A/ACP) where, upon the onset of a GnRHa-induced bleed, the agonist is supplanted by an antagonist (Ganirelix/Cetrotide/Orgalutron) and this is continued until the hCG trigger. In many such cases I often supplement with human growth hormone (HGH) in such cases in an attempt to enhance egg mitochondrial activity and so enhance egg development. This approach is often augmented with preimplantation genetic screening (PGS) of all embryos that reach the expanded blastocyst stage of development by day 5-6 post-fertilization. I also commonly recommend blastocyst banking to many such patients.
2. Short (“Flare”) GnRHa Protocol: Another GnRHa usage for COS is the so called “(micro) flare protocol”. This involves initiating gonadotropin therapy commensurate with initiation of gonadotropin administration. The supposed objective is to deliberately allow Lupron to elicit an initial surge (“flare”) in pituitary FSH release in order to augment FSH administration by increased FSH production. Unfortunately, this “spring board effect” constitutes “a double-edged sword”. While it indeed increases the release of FSH, it at the same time causes a surge in LH release. The latter can evoke excessive ovarian stromal/thecal androgen production which could potentially compromise egg quality, especially when it comes to older women and women with DOR. I am of the opinion that by evoking an exaggerated ovarian androgen response, such “(micro) flare protocols” can harm egg/embryo quality and reduce IVF success rates, especially when it comes to COS in older women, and in women with diminished ovarian reserve. Accordingly, I do not prescribe such protocols to my IVF patients.
3. Estrogen Priming – This is the approach I sometimes prescribe for my patients who have virtually depleted ovarian reserve , as determined by very low blood anti-Mullerian hormone AMH levels (<0.2ng/ml or 2 pmol/L) and are thus likely to be very “poor responders”. It involves a modified A/ACP. We start with estrogen skin patches applied every 2nd day (or with the BCP) for 10 days or longer, overlap it for 3 days with a GnRHa whereupon the estrogen priming is stopped. Th GnRHa is continued until the onset of menstruation (usually 5-7 days later) to cause pituitary LH, down-regulation. Upon menstruation and confirmation by ultrasound and measurement of blood estradiol levels that adequate ovarian suppression has been achieved, The patient is given twice-weekly injections of estradiol valerate (Delestrogen) for a period of 7-8 days whereupon COS is initiated using a relatively high dosage FSH-(Follistim, Fostimon, Puregon or Gonal F), which is continued along with daily administration of GnRH antagonist until the “hCG “trigger.” This approach is often augmented with HGH administration throughout the process of COS and by preimplantation genetic screening (PGS) of all embryos that reach the expanded blastocyst stage of development by day 5-6 post-fertilization. I also commonly recommend blastocyst banking to many such patients.
Estrogen Priming has succeeded in significantly enhancing ovarian response to gonadotropins in many of otherwise very poor responders.
Triggering egg Maturation prior to egg Retrieval: hCG versus GnRHa
With ovulation induction using fertility drugs, the administration of 10,000U hCGu (Pregnyl; Profasi, Novarel) or 500mcg hCGr (Ovidrel/Ovitrel) “trigger”) sends the eggs (into maturational division (meiosis). This process is designed to halve the chromosome number, resulting in mature eggs (M2) that will have 23 chromosomes rather that the 46 chromosomes they had prior to the “trigger”. Such a chromosomally numerically normal (euploid), mature (MII) eggs, upon being fertilized will (hopefully) propagate euploid embryos that have 46 chromosomes and will be “: competent” to propagate viable pregnancies. In my opinion, the key is to always “trigger” with no less than 10,000U of hCGu or 500mcg hCGr (Ovidrel/Ovitrel). Any lesser dosage often will reduce the efficiency of meiosis and increase the risk of the eggs being aneuploid. I personally do not use the agonist (Lupron) “trigger”, unless it is combined with (low dosage) hCG. The supposed reason for using the agonist, (Lupron) “trigger” is that by inducing meiosis through compelling a surge in the release of LH by the pituitary gland, the risk it reduces the risk of OHSS. This may be true, but it comes at the expense of egg quality because the extent of the induced LH surge varies and if too little LH is released, meiosis can be compromised, thereby increasing the likelihood of aneuploid and immature (MI) eggs. And there are other better approaches to preventing OHSS (e.g. “prolonged coasting”), in my opinion.
Use of the Birth Control Pill (BCP) to launch IVF-COS.
In natural (unstimulated) as well as in cycles stimulated with fertility drugs, the ability of follicles to properly respond to FSH stimulation is dependent on their having developed FSH-responsive receptors. Pre-antral follicles (PAF) do not have such primed FSH receptors and thus cannot respond properly to FSH stimulation with gonadotropins. The acquisition of FSH receptor responsivity requires that the pre-antral follicles be exposed to FSH, for a number of days (5-7) during which time they attain “FSH-responsivity” and are now known as antral follicles (AF). These AF’s are now able to respond properly to stimulation with administered FSH-gonadotropins. In regular menstrual cycles, the rising FSH output from the pituitary gland insures that PAFs convert tor AF’s. The BCP (as well as prolonged administration of estrogen/progesterone) suppresses FSH. This suppression needs to be countered by artificially causing blood FSH levels to rise in order to cause PAF to AF conversion prior to COS commencing, otherwise pre-antral-to –antral follicle conversion will not take place in an orderly fashion, the duration of ovarian stimulation will be prolonged and both follicle and egg development may be compromised. GnRH agonists cause an immediate surge in release of FSH by the pituitary gland thus causing conversion from PAF to SAF. This is why women who take a BCP to launch a cycle of COS need to have an overlap of the BCP with an agonist. By overlapping the BCP with an agonist for a few days prior to menstruation the early recruited follicles are able to complete their developmental drive to the AF stage and as such, be ready to respond appropriately to optimal ovarian stimulation. Using this approach, the timing of the initiation of the IVF treatment cycle can readily and safely be regulated and controlled by varying the length of time that the woman is on the BCP.
Since optimizing follicular response to COS requires that prior to stimulation with gonadotropins, FSH-induced conversion from PAF to AF’s first be completed and the BCP suppresses FSH, it follows when it comes to women launching COS coming off a BCP something needs to be done to cause a rise in FSH for 5-7 days prior to menstruation heralding the cycle of CO S. This is where overlapping the BCP with a GnRHa comes in. The agonist causes FSH to be released by the pituitary gland and if overlapped with the BCP for several days and this will (within 2-5 days) facilitate PAF to AF conversion…. in time to start COS with the onset of menstruation. Initiating ovarian stimulation in women taking a BCP, without doing this is suboptimal.
I strongly recommend that you visit www.SherIVF.com. Then go to my Blog and access the “search bar”. Type in the titles of any/all of the articles listed below, one by one. “Click” and you will immediately be taken to those you select. Please also take the time to post any questions or comments with the full expectation that I will (as always) respond promptly.
• The IVF Journey: The importance of “Planning the Trip” Before Taking the Ride”
• Controlled Ovarian Stimulation (COS) for IVF: Selecting the ideal protocol
• The Fundamental Requirements For Achieving Optimal IVF Success
• Use of GnRH Antagonists (Ganirelix/Cetrotide/Orgalutron) in IVF-Ovarian Stimulation Protocols.
• Anti Mullerian Hormone (AMH) Measurement to Assess Ovarian Reserve and Design the Optimal Protocol for Controlled Ovarian Stimulation (COS) in IVF.
• The “Biological Clock” and how it should Influence the Selection and Design of Ovarian Stimulation Protocols for IVF.
• A Rational Basis for selecting Controlled Ovarian Stimulation (COS) protocols in women with Diminished Ovarian Reserve (DOR)
• Diagnosing and Treating Infertility due to Diminished Ovarian Reserve (DOR)
• Ovarian Stimulation in Women Who have Diminished Ovarian Reserve (DOR): Introducing the Agonist/Antagonist Conversion protocol
• Controlled Ovarian Stimulation (COS) in Older women and Women who have Diminished Ovarian Reserve (DOR): A Rational Basis for Selecting a Stimulation Protocol
• Optimizing Response to Ovarian Stimulation in Women with Compromised Ovarian Response to Ovarian Stimulation: A Personal Approach.
• Egg Maturation in IVF: How Egg “Immaturity”, “Post-maturity” and “Dysmaturity” Influence IVF Outcome:
• Commonly Asked Question in IVF: “Why Did so Few of my Eggs Fertilize and, so Many Fail to Reach Blastocyst?”
• Human Growth Hormone Administration in IVF: Does it Enhances Egg/Embryo Quality and Outcome?
• The BCP: Does Launching a Cycle of Controlled Ovarian Stimulation (COS). Coming off the BCP Compromise Response?
• Staggered IVF
• Staggered IVF with PGS- Selection of “Competent” Embryos Greatly Enhances the Utility & Efficiency of IVF.
• Staggered IVF: An Excellent Option When. Advancing Age and Diminished Ovarian Reserve (DOR) Reduces IVF Success Rate
• Embryo Banking/Stockpiling: Slows the “Biological Clock” and offers a Selective Alternative to IVF-Egg Donation
• Preimplantation Genetic Testing (PGS) in IVF: It should be Used Selectively and NOT be Routine.
• IVF: Selecting the Best Quality Embryos to Transfer
• Preimplantation Genetic Sampling (PGS) Using: Next Generation Gene Sequencing (NGS): Method of Choice.
• PGS in IVF: Are Some Chromosomally abnormal Embryos Capable of Resulting in Normal Babies and Being Wrongly Discarded?
• PGS and Assessment of Egg/Embryo “competency”: How Method, Timing and Methodology Could Affect Reliability
• IVF outcome: How Does Advancing Age and Diminished Ovarian Reserve (DOR) Affect Egg/Embryo “Competency” and How Should the Problem be addressed.

Founded in April 2019, Sher Fertility Solutions (SFS) offers online (Skype/FaceTime) consultations to patients from > 40 different countries. All consultations are followed by a detailed written report presenting my personal recommendations for treatment of what often constitute complex Reproductive Issues.

If you wish to schedule an online consultation with me, please contact my assistant (Patti Converse) by phone (800-780-7437/702-533-2691), email (concierge@SherIVF.com) or, enroll online on then home-page of my website (www.SherIVF.com).


Geoff Sher


Hi Dr. Sher,

Thank you for providing so much information on your blog. I am wondering if you can tell us your thoughts on any differences between Day 5 blasts vs Day 6 blasts for a frozen cycle (in terms of achieving a viable pregnancy). Thank you.

Dr. Geoffrey Sher

Both are fine….and if they are both chromosomally normal (PGS-normal) they are equally good. If no PGS was done, then I would favor the day-5 blastocyst!~

Geoff Sher


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