IVF TREATMENT: How Does It Work?
1. CONTROLLED OVARIAN HYPERSTIMULATION (COH)
IVF success rates are dependent upon the number of the mature eggs and healthy embryos available for transfer. A woman undergoing IVF is given fertility drugs for two reasons: (1) to improve the growth and development of her ovarian follicles in order to produce as many healthy eggs as possible and (2) to control the timing of ovulation so that the eggs can be retrieved before ovulation, with as many of them mature as possible. In cases where the woman has previously received fertility drugs, the subsequent treatment regime is largely based upon her most past response to such treatment. For a woman receiving gonadotropins for the first time, the dosage and regimen is determined by her blood follicle stimulating hormone (FSH) and estradiol (E2) concentrations on the 3rd day of her menstrual cycle, medical history, body habits and other variables.
In most cases, the woman begins her cycle of treatment by taking oral contraceptive birth control pills (OCP/BCP) before initiating daily injections of leuprolide acetate (Lupron). Both the OCP/BCP and Lupron are administered together for an additional 5-7 days where upon the BCP is withdrawn while daily Lupron injections are continued. Menstruation will usually follow about 2-7 days after stopping the BCP. This way it is possible to accurately plan the onset of menstruation by varying the length of time on the BCP and schedule each cycle of IVF. Additionally, the combined use of BCP and Lupron reduces the risk of Lupron-induced ovarian cyst formation, thereby largely avoiding the need to delay or cancel the cycle of treatment.
As soon as menstruation begins, blood is drawn and if the plasma E2 concentration is less than 60 pg/ml, the patient is ready to initiate ovarian stimulation with gonadotropins. If the E2 level is greater than 60 pg/ml, Lupron therapy is continued at the same (or at an increased) dosage for a few more days, whereupon the E2 concentration is re-measured. Subsequent failure of the E2 to fall below 60 pg/ml is an indication for a pelvic ultrasound for the detection of an ovarian cyst, the presence of which usually mandates the performance of an ovarian cyst needle aspiration or delay or cancellation of the cycle.
Lupron injections are either continued at a reduced daily dosage or stopped and switched to low dose GnRH antagonist (Ganirelix or Cetrotide). On a designated day (usually within a week and a half of the onset of menstruation), a specified regimen of gonadotropins (e.g., Gonal F, Follistim, Bravelle, Repronex, Menopur) therapy is initiated. Some patients receive Estradiol Valerate (E2V) injections and/or vaginal estradiol suppositories for a week or longer prior to and during gonadotropin therapy.
Most IVF patients receive oral dexamethasone 0.75 mg (1 tablet) daily, beginning a few days prior to the egg retrieval and continuing until the first blood beta-HCG test (i.e., the chemical diagnosis of pregnancy). Women, who have a positive blood pregnancy test 8-10 days after embryo transfer, continue taking dexamethasone beyond the ultrasound confirmation of pregnancy, which is performed at the 6-7 gestational week. In cases where the blood pregnancy test fails to reveal an appropriate increase in the quantitative beta HCG concentration, dexamethasone dosage is slowly reduced over time and then stopped. Pregnant women continue dexamethasone until the 7th week of pregnancy, whereupon it is tapered off and stopped. All patients receive oral doxycycline (antibiotic) before the egg aspiration and continue for a few days after the embryo transfer procedure. In most cases two days after the initiation of gonadotropin injections, the dosage of gonadotropins is substantially reduced, and is then maintained at this lower level until the administration of HCG. Dosage adjustments are sometimes made during the course of the cycle, based upon the patient’s response to medication.
Starting seven days after the initiation of gonadotropin therapy, the patient undergoes serial ultrasound and plasma estradiol evaluations to monitor her ovarian response. These assessments are aimed at determining the ideal day for administering 10,000 IU HCG to trigger the final maturation of the egg(s) and the production of progesterone by the ovaries. Lupron or Ganirelix/Cetrotide and gonadotropin injections are discontinued on this day and the patient is scheduled for egg retrieval approximately 35 hours after receiving the injection of HCG.
2. THE EGG RETRIEVAL
Egg retrieval involves a procedure where under direct ultrasound guidance, a needle is passed along the side of a vaginal ultrasound probe through the top of the vagina into follicles (small fluid filled spaces that each contain an egg) within the ovary(s). The follicular fluid and the egg are aspirated and collected in a sterile tube, which is handed directly to the embryologist for evaluation and fertilization. The procedure itself is painless because it is done under anesthesia, however patients commonly experience some residual postoperative abdominal discomfort and/or cramping that rarely persists for more than a few hours. Anesthesia used for egg retrieval procedures are administered through the IV and results in loss of consciousness (preventing patients from feeling the pain and discomfort during the procedure). This type of anesthesia does not require intubation (placement of tube in the mouth/throat) but rather a deep sleep. Postoperatively all patients are given detailed instructions and are discharged within an hour with a prescription for analgesics (pain killers) and other medications as indicated.
3. SPERM PROCESSING
Sperm is usually obtained through masturbation specimen from the male partner. On some occasions physical, medical and/or religious constraints demand that sperm be obtained through condom collection following intercourse, or by inserting a needle directly into the testicle(s) under local anesthesia and aspirating sperm Testicular Sperm Extraction (TESE) or Percutaneus Epididymal Sperm Aspiration (PESA). TESE or PESA are procedures of choice in cases where there is blockage of the sperm ducts (as occurs following vasectomy or following severe injury or infection), or where the man is born without sperm ducts (congenital absence of the vas deferens). Sometimes, in cases of retrograde ejaculation, sperm can be collected from the man’s bladder. Infrequently, in men with spinal cord injuries, ejaculation is facilitated by electrical stimulation (electro-ejaculation). Donor sperm, obtained from a sperm bank can be used when indicated.
Sperm must undergo biochemical and structural changes known as capacitation, before an egg can be fertilized. Capacitation (which under normal circumstances takes place in the woman’s reproductive tract) must be accomplished in the embryology laboratory prior to insemination of the eggs. Motile sperm are processed and used for fertilization.
“In vitro” fertilization means “fertilization in the laboratory” rather than inside the fallopian tubes. Aspirated ovarian follicles are examined in the embryology laboratory, the eggs are identified, extracted and are placed in a special culture medium. Several hours later, approximately 25,000 -100,000 processed sperm are placed around each of the eggs. The eggs and sperm are allowed to incubate together in a carefully controlled environment. Approximately 16-24 hours later, the eggs are inspected microscopically for fertilization as evidenced by the presence of two nuclear bodies. These binuclear unicellular bodies are referred to as “pro-nuclear embryos”.
Intracytoplasmic sperm injection (ICSI) has revolutionized the treatment of male infertility. The procedure involves the direct injection of a single sperm into each egg under direct microscopic vision. The successful performance of ICSI requires a high level of technical expertise. When ICSI is employed, the IVF birth rate is very high in the presence of male infertility. In fact, even when the absence of sperm in the ejaculate requires that ICSI be performed on sperm obtained through Testicular Sperm Extraction (TESE) or PESA, the success rates are high.
The introduction of ICSI has made it possible to fertilize eggs with sperm derived from men with severe degrees of male infertility. The indications for ICSI have broadened dramatically, with the process now being used for a variety of indications other than male factor infertility. We also use ICSI to assist in the fertilization of eggs that are believed to have a hardened or thickened outer envelopment (zona pellucida). This is frequently found in the association with polycystic ovarian disease (PCO) and in eggs derived from older women (over 40 years). ICSI is also frequently recommended in cases of “unexplained infertility” and where there is a history of poor fertilization during one or more prior IVF attempts.
Assisted Hatching: In selected cases where it is felt that the zona pellucida (the envelopment of the embryo/blastocyst) is unusually tough or thickened, history of failed IVF attempts or women above the age of 38, a process known as Assisted Hatching (AH) may be employed. The process involves deliberately weakening the wall of the embryo mechanically (using laser) or chemically (using acid tyrode solution), so as to promote hatching (rupturing) and thereby facilitate implantation. We utilize a state of the art laser to perform AH at our embryology laboratory.
Embryos/blastocysts are transferred to the uterus via a thin catheter. This procedure is often conducted under ultrasound guidance with the woman on her back (in the lithotomy position) and with a full bladder. The procedure is usually painless and takes less than ten minutes to complete. Sometimes a prior trial embryo transfer points towards potential difficulty in transferring the embryo to the uterus. In such cases, the procedure may be performed with patient under anesthesia. In rare cases where tortuous or partial obstruction of the canal leading in to the uterus (i.e. the cervical canal) severely complicates conventional embryo transfer, a method known as Transmyometrial Embryo Transfer (TMET) can be used. With TMET, the patient is anesthetized and a needle is passed along the side of a transvaginal ultrasound probe, through the wall of the uterus into the cavity. A catheter is passed through the needle with its tip protruding into the uterine cavity. The needle is partially withdrawn and the embryo is injected into the endometrial cavity. After the embryo transfer the woman remains immobile for a short period of time and is thereupon discharged with specific instructions.
5. THE EMBRYO TRANSFER (ET):
Embryo transfer is a rate limiting step in IVF and can be done 3 or 5 days following fertilization. It takes confidence, dexterity, skill and gentility to do a good embryo transfer. Once cleavage has begun, the embryo will continue to divide at regular intervals. (Embryos that divide the fastest are considered the healthiest and the most likely to implant.) Once the lead (fastest growing) embryo reaches the four‑ to eight-cell stage, the embryos can be transferred into the uterus or observed until the blastocyst stage and are transferred on day 5. Embryos that do not comprise at least 6 blastomeres within 72 hours of insemination or ICSI– or do not reach the blastocyt stage by day 5– are usually non-viable and will not produce a baby.
Embryo transfers should be performed under direct ultrasound guidance to ensure proper placement in the uterine cavity. This practice can significantly enhance embryo implantation/pregnancy rates and also allows visual participation of the patient/couple. We prefer to perform all embryo transfers when the woman has a full bladder. This facilitates the visualization of the uterus by abdominal ultrasound and would tilt the uterus into a straight position. The patient is allowed to empty her bladder following the embryo transfer. We also offer our patients oral diazepam (Valium) prior to the embryo transfer to relax them and reduce apprehension.
When the patient is in the proper position, and her bladder is adequately filled, the physician first inserts a speculum into the vagina to expose the cervix and then may clean the cervix with a solution to remove any mucus or other secretions. An abdominal ultrasound transducer is placed suprapubically on the lower abdomen and the uterus is visualized. The physician then informs the embryology laboratory that embryo transfer is imminent and awaits the arrival of the transfer catheter that will be loaded with the embryos. The physician gently guides the catheter through the woman’s cervix into the uterine cavity. When the catheter is in place, the embryologist carefully injects the embryos into the uterus, and the physician slowly withdraws the catheter. The catheter is immediately returned to the laboratory, where it is examined under the microscope to make sure that all the embryos have been deposited. Any residual embryos would be re-incubated, and the transfer process would usually be repeated to deliver the remaining embryos. Transfer of residual embryos neither harms the embryos nor reduces the pregnancy rates.
6. POST-EMBRYO TRANSFER MANAGEMENT:
Immediately prior to being discharged following the embryo transfer procedure, an exit interview is conducted whereby the patient is given written instructions. Hormonal supplementation usually involves the administration of intramuscular injections of progesterone and/or a vaginal suppository (comprising estradiol valerate and micronized progesterone) until a blood pregnancy test is performed approximately 8-10 days later (the chemical diagnosis of pregnancy). In selected cases, such progesterone treatment can be replaced with Crinone vaginal applications once or twice daily. If the pregnancy test is negative or the plasma HCG levels fail to rise appropriately in the ensuing days, all hormonal support is discontinued. Intramuscular progesterone injections are continued along with vaginal estradiol and progesterone suppositories until the 10-12th week of pregnancy. An ultrasound examination is performed approximately 2-3 weeks after the chemical diagnosis of pregnancy to visualize the pregnancy and hear the heartbeat.
7. EMBRYO/BLASTOCYST CRYOPRESERVATION:
There have been dramatic advances in the technology of freezing and storing human embryos for future use. We cryopreserve (freeze) embryos one day after fertilization (the pronucleate stage), on the 3rd day (provided they have attained the 8-cell stage of division) or as blastocysts, depending upon patient-specific indications and choices. Regardless of when the freezing process is done, we usually transfer in the blastocyst stage. This means that pronucleate and day three embryos are thawed and cultured for an additional few days. Those that attain the blastocyst stage of development are eligible for transfer to the uterus. Frozen blastocysts are thawed and transferred a few hours later. Recent technological advances have enhanced embryo/blastocyst freeze-thaw survival rates, resulting in a significant improvement in pregnancy rates following Frozen Embryo Transfers (FET). We currently observe a high pregnancy rate following FET.
It should be appreciated that approximately 10-20% of frozen embryos will likely be lost during the freeze-thaw process. Available evidence suggests that the replacement of thawed embryos/blastocysts does not increase the risk of birth defects. Using the ultra-rapid freezing technique called vitrification survival rates following freezing-thawing of the embryos have significantly improved.