It is primarily the egg (rather than the sperm) that determines the chromosomal integrity (karyotype) of the embryo, the most important determinant of egg/embryo competency”. A “competent” egg is therefore one that has a normal karyotype and has the best potential to propagate a “competent” embryo. In turn, a “competent embryo is one that possesses the highest potential to implant and develop into a normal, healthy, baby.
When it comes to reproductive performance, humans are the least efficient of all mammals. Even in young women under 35y, at best only 2 out of 3 eggs are chromosomally numerically normal (euploid). The remainder will have an irregular number of chromosomes (aneuploid) and are thus “incompetent”. The incidence of egg aneuploidy increases with age such by age 39 years, 3 in 4 are “competent”, and by the mid-forties, at best one in 10 are likely to be aneuploid. The fertilization of an aneuploid egg will inevitably lead to embryo aneuploidy (“incompetence”). As previously stated, an aneuploid embryo cannot propagate a normal pregnancy
Within 38-42 hours of the initiation of the spontaneous pre-ovulatory luteinizing hormone (LH) surge (and also following administration of the human chorionic gonadotropin (hCG) “trigger” shot, given to induce egg maturation after ovarian stimulation with fertility drugs), the egg embarks on a rapid maturational process that involves halving of its 46 chromosomes to 23. During this process, (known as meiosis) 23 chromosomes are retained within the nucleus of the egg while the remaining 23 chromosomes are expelled in a membrane envelopment, from the egg nucleus. This small structure known as the polar body, comes to lie immediately below the “shell” of the egg (the zona pellucida) and is known as the 1st polar body or PB-1. The sperm, in the process of its maturation also undergoes meiosis divides into two separate functional gametes, each containing 23 chromosomes (half its original number of 46 chromosomes). With subsequent fertilization, the 23 chromosomes of the egg now fuse with the 23 chromosomes of the mature sperm resulting in the development of an embryo with 46 chromosomes (the normal human genome) comprising a combination of the genetic material from both partners. For the embryo to have exactly 46 chromosomes (the euploid number), both the mature egg and mature spermatozoon must contain exactly 23 chromosomes. Only such euploid embryos are “competent” (capable of developing into healthy babies). Those with an irregular number of chromosomes (aneuploid embryos) are “incompetent” and are incapable of propagating healthy babies. While embryo “incompetence” can result from either egg or sperm aneuploidy, it usually stems from egg aneuploidy. However, in cases of moderate or severe male factor infertility, the sperm’s contribution to aneuploidy of the embryo can be significantly greater.
While embryo ploidy (numerical chromosomal integrity) is not the only determinant of its “competency, it is by far the most important and in fact is a rate-limiting factor in human reproduction. It is causal in the vast majority of cases of “failed nidation which in turn is responsible for most cases of a failed pregnancy (natural or assisted) and causes most sporadic early pregnancy losses (both chemical gestations and miscarriages) as well as many chromosomal birth defects such as Turner syndrome (X-monosomy ) Down syndrome (trisomy 21) and Edward syndrome (trisomy 18) .
In most cases, embryos that develop too slowly as well as those that grow too fast (i.e. ones that by day 3 post-fertilization comprise fewer than 6 cells or more than 9 cells) and/or embryos that contain cell debris or “fragments” are usually aneuploid and are thus unable to propagate a healthy pregnancy (“incompetent”). Additionally, embryos that fail to survive in culture to the blastocyst stage are also almost always aneuploid/”incompetent”.
At a certain point in the later stage of a woman’s reproductive career, the number of remaining eggs in her ovaries falls below a certain threshold, upon which she is unable to respond optimally to fertility drugs. Often times this is signaled by a rising day 3 basal blood follicle stimulating hormone (FSH) level (>9.0MIU/ml) and a falling blood anti-Mullerian hormone (AMH) level (<2.0ng/ml or <15nmol/L). Such women who have diminished ovarian reserve (DOR) produce fewer eggs in response to ovarian stimulation. While DOR is most commonly encountered in women over 40 years of age it can and indeed also can occur in much younger women.
A few important (but often overlooked concepts should be considered in this regard:
- Age: It is advancing chronologic age and NOT declining ovarian reserve (as evidenced by abnormal blood AMH or FSH that results in an increased incidence of egg/embryo “incompetence” due to aneuploidy
- The ovaries and developing eggs of women with DOR (regardless of age) are highly susceptible to the adverse effect of excessive Luteinizing Hormone (LH)-induced, ovarian overproduction of male hormones (e,g. testosterone and androstenedione). While a little testosterone produced by the ovary promotes normal follicle growth and orderly egg development excessive testosterone has a converse effect. That is why in older women and those who regardless of their age have DOR (and thus excessive LH bioavailability and increased ovarian testosterone production), the use of ovarian stimulation protocols that fail to down-regulate LH activity prior to initiating ovarian stimulation with gonadotropins, often prejudices egg/embryo quality and IVF outcome.
- Simply stated, while age is certainly the most important factor in determining the incidence of egg/embryo aneuploidy, women with DOR (regardless of their age), are less likely to propagate euploid (competent) eggs/embryos. While virtually nothing can be done to lower the incidence of age related aneuploidy, it is indeed possible to avoid a further decrease in egg/embryo “competency” by individualizing the protocols of ovarian stimulation used.
- My preferred protocols for women who have relatively normal ovarian reserve:
- The conventional long pituitary down regulation protocol: BCP are commenced early in the cycle and continued for at least 10 days. Starting 3 days before the BCP is to be discontinued, it is overlapped with an agonist such as Lupron 10U daily for three (3) days and continued until menstruation begins (which should ensue within 5-7 days of stopping the BCP). At that point an US examination is done along with a baseline measurement of blood estradiol to exclude a functional ovarian cyst. Daily Lupron (10U) is continued and an FSH-dominant gonadotropin such as Follistim, Puregon or Gonal-f daily is administered daily falong with 37.5U of Menopur (an FSH/LH combination) for 2 days. On the 3rd day the gonadotropin dosage is reduced by about one half and the dosage of Menopur is increased to 75U daily. Daily ultrasound and blood estradiol measurements are conducted starting on the 7th or 8th day of gonadotropin administration and continued until daily ultrasound follicle assessments indicate that most follicles have fully developed. At this point egg maturation is “triggered” using an intramuscular injection of a recombinant hCGr (Ovidrel) 500mcg or urinary derived hCGu (Pregnyl/Profasi/Novarel) 10,000U. And an egg retrieval is scheduled for 36h later.
- The agonist/antagonist conversion protocol (A/ACP): This is essentially the same as the conventional long down regulation protocol (see “a”-as above), except that with the onset of post-BCP menstruation, the agonist is supplanted by daily administration of a GnRH antagonist (e.g. Ganirelix, Cetrotide or Orgalutron) at a dosage of 125-250mcg daily until the day of the “trigger”. When it comes to women who have DOR I favor the use of the A/ACP, adding supplementary human growth hormone (HGH). In cases where the DOR is regarded as severe (AMH=<0.2), I often augment the AACP protocol by using estrogen priming for 7-9 days prior to or with the commencement of gonadotropin therapy; For this I prescribe E2 skin patches or intramuscular estradiol valerate (Delestrogen), prior to or sometimes concurrent with, the commencement of the GnRH antagonist administration.
- The following Ovarian stimulation protocols are in my opinion best avoided in stimulating olderf women and /or thosed who regardless of age , have DOR :
- Microdose agonist (e.g. Lupron) “flare” protocols which result in an out-pouring of pituitary-LH at the critical time that ovarian follicles and eggs start developing/growing.
- High dosages of LH -containing fertility drugs (e.g. Menopur).
- Supplementation with preparations that are testosterone-based
- Supplementation with DHEA (which is converted to testosterone in the ovaries.
- Clomiphene citrate or Letrozole which cause increased release of LH and thus increase ovarian male hormone (testosterone and androstenedione output.
- “Triggering” egg maturation using too low a dosage of hCG (e.g. 5,000U rather than 10,000U) or Ovidrel (e.g. 250mcg of Ovidrel rather than 500mcg)
- “Triggering” women who have DOR, with an agonist (alone)such as Lupron Superfact/ Buserelin/Aminopeptidyl/Decapeptyl.
- Preimplantation Genetic Screening (PGS):
The introduction of preimplantation genetic testing/screening (PGT/PGS) for e permits identification of all the chromosomes in the egg and embryo (full karyotyping) allowing for the identification of the most “competent” (euploid) embryos for selective transfer to the uterus. This vastly improves the efficiency and success of the IVF process and renders us fare better equipped us to manage older women and those who regardless of their age, have DOR.