In Vitro Fertilization

Anatomy and Physiology

Recognition of female pelvic anatomy is paramount in properly understanding and completing IVF. In order to achieve optimal results in IVF, certain types of anatomy appear to be associated with success rates of oocytes retrieval and embryo transfer. The uterus is a Mullerian structure of the female pelvis that provides an environment to harbor a growing pregnancy. The uterus is composed of three layers, the serosa, the myometrium, and the endometrium. The endometrium or the lining of the uterus is a structure of glandular tissue that undergoes predictable changes during the menstrual cycle in response to levels of circulating hormones.  

Approximately 10% to 15% of couples will have difficulties getting pregnant.  Infertility is defined as no conception after 12 months of unprotected sexual intercourse in women less than 35 or six months in women 35 years or older.[3] If the female partner has oligomenorrhea or amenorrhea, endometriosis, tubal disease, or there is a known male issue, an earlier evaluation is indicated.[4] The workup for couples experiencing infertility includes an assessment of ovulatory function, ovarian reserve, uterine cavity, tubal patency, and a semen analysis.  If there is evidence of endometriosis, tubal occlusions, or adnexal adhesions then a diagnostic laparoscopy should be considered.

Indications

Approximately 25% to 35% of infertile women are found to have tuboperitoneal disease, with pelvic inflammatory disease (PID) being the most common cause of tubal damage.[5] PID is usually a result of Chlamydia trachomatis infections.[6] Bacterial infections can result in tubal occlusion or peritubular adhesions that render in vivo fertilization unlikely. IVF bypasses the tubal damage by transferring embryos directly into the uterus.

Endometriosis, a chronic inflammatory disease defined by the presence of endometrial tissue outside of the uterine cavity, is significantly more prevalent in women with infertility compared to those without.[7] The mechanisms of how endometriosis causes infertility are not yet fully understood, but research has shown that pelvic adhesions, chronic intraperitoneal inflammation, disturbed folliculogenesis, and decreased embryo implantation have all been described in women with endometriosis. Laparoscopic surgery has been found to increase the rate of pregnancy from 4.7% to 30.7%, indicating the importance of restoring normal pelvic anatomy for a spontaneous pregnancy. Unfortunately, women with endometriosis have a significantly lower success rate with IVF compared to other causes of infertility, with more advanced disease correlated to inferior outcomes.[8]

Poor semen quality is the sole cause of infertility in 20% of couples and contributes to fertility issues in another 20%. Decreased sperm count, motility, or morphology (shape of the sperm) can be successfully treated medically or surgically in approximately 50% of men. Intrauterine insemination can also increase pregnancy rates in couples where the male partner has a low number of motile sperm. If such treatments fail, IVF with or without intracytoplasmic sperm injection (ICSI) can be utilized. Sperm extracted from the testicle or epididymis in cases of obstructive azoospermia or testicular hypofunction can only be used in an IVF cycle with ICSI as the sperm have not undergone the final in vivo maturation process, allowing it to fertilize an oocyte.

Women who are unable to produce their own oocytes due to POI or diminished ovarian reserve are able to become pregnant with donor oocytes or donor embryos. IVF cannot overcome the impact of age on oocyte function and fertilizability, and so many women in their late 30’s and older will use donor oocytes. These oocytes have been removed from a younger woman (usually less than 30 years of age) and are either frozen for future use or used in a fresh IVF cycle.

IVF is also utilized in women who desire to preserve their fertility. Women with cancer or other illnesses may need to undergo gonadotoxic treatments that pose a threat to ovarian function. These women can cryopreserve either oocytes or embryos prior to chemotherapy or radiation that then can be transferred at a future time.

Oocyte cryopreservation is also a viable option for women who wish to delay childbearing. It is well established that women’s fertility dramatically decreases in the fourth decade of life. This drop-in fecundability is a result of a decrease in both oocyte quantity and quality. Women who are not interested in pregnancy in the near future can cryopreserve oocytes for future use.[9]

Contraindications

There are no absolute contraindications to the procedure of IVF. However, it should not be performed in women who have a significant risk of morbidity and mortality of pregnancy if IVF were successful. Some examples of these high-risk conditions include but are not limited to Marfan syndrome, New York Heart Association (NYHA) class 3 or 4 heart failure, Eisenmenger syndrome, severe valvular stenosis, pulmonary hypertension, or coarctation of the aorta. For women with these significant medical issues who desire a biological child, they can undergo IVF with oocyte aspiration, fertilization with their partner’s sperm, but the embryos will be transferred to a gestational carrier.

Equipment

For the embryology lab:

• Triple gas control incubators
• MultiBlok heaters
• Precision water bath
• Stage warmers
• Hoods with a stereomicroscope and heated stage
• Inverted microscopes with micromanipulation technology (ICSI)
• Anti-vibration tables
• Laser for embryo biopsy for preimplantation genetic diagnosis (PGT)
• Tabletop incubators for embryo culture
• Air-filtration systems
• Alarm system
• Wireless monitoring systems for liquid nitrogen tanks
• Liquid nitrogen tanks for sperm, oocyte and embryo cryopreservation

Personnel

The practice committee of the American Society for Reproductive Medicine recommends the following:[10]

• A physician who has completed an American College of Graduate Medical Education approved a three-year fellowship in reproductive endocrinology and infertility and is board certified by the American Board of Obstetrics and Gynecology.
• Nurse with training in reproductive medicine and clinical assisted reproductive technologies
• Physician or nurse trained in gynecological ultrasonography
• Embryology laboratory director (Ph.D. or MD) with a high complexity laboratory director or embryology laboratory director certification
• Embryology laboratory personnel trained in gamete and embryo cryopreservation and micromanipulation techniques

Preparation

Individuals planning for IVF undergo several evaluations prior to the start of the treatment cycle. The woman’s ovarian reserve is evaluated using either cycle day three follicle-stimulating hormone (FSH) and estradiol (E2), anti-Mullerian hormone (AMH), or antral follicle count. If the woman is determined to have poor ovarian reserve based on any of these values, she can still pursue IVF but may need to consider the use of donor oocytes.

The male partner has a semen analysis to decide whether ICSI is indicated, based on sperm morphology, count, and motility. Uterine cavity imaging identifies any anatomical issues, including endometrial polyps or fibroids, adhesions, or septa that may interfere with embryo implantation. Infectious disease screening for HIV, hepatitis B, and C and syphilis is recommended for both partners.

Technique or Treatment

Controlled Ovarian Stimulation

The cycle of IVF begins with ovarian stimulation. Multiple protocols have been utilized, including no stimulation to various levels of ovarian stimulation using clomiphene citrate, letrozole, and exogenous gonadotropins (FSH and luteinizing hormone (LH)). In IVF cycles, gonadotropin-releasing hormone (GnRH) analogs are utilized to eliminate the woman’s LH surge allowing the physicians to time oocyte retrieval. Follicular growth is monitored by transvaginal ultrasonography, and blood levels of E2 help determine any indicated changes in the stimulation protocol.

In natural cycle IVF, the oocyte is retrieved before the mid-cycle LH surge occurs, or a GnRH antagonist (GnRHant) is used to prevent the release of LH. When the lead follicle reaches a mature size, hCG is given as a substitute for the LH surge. The pregnancy rate is about 8% per cycle with a 21% cumulative rate after three cycles, with rates as high as 44% in couples with male factor infertility. Natural cycle IVF is not commonly performed because of the lower clinical pregnancy rate.[11]

Ovarian stimulation is done in the vast majority of IVF cycles so that approximately 10 to 20 oocytes are retrieved.  There are two main protocols; long luteal GnRH agonist (GnRHa) or a GnRHant cycle.

The long luteal GnRHa protocol begins with the administration of 0.1 mg GnRHa daily starting on cycle-day 21 in the preceding month. This turns off the pituitary secretion of LH (and FSH) during the ovarian stimulation, and the GnRHa is continued until the hCG injection. Gonadotropins are injected at doses ranging from 75 to 450 IU daily starting on cycle day 2 with dose adjustments based on follicular development and estradiol levels. The hCG injection is administered when at least three follicles reach 18 mm in size.

The GnRHant protocol entails the administration of daily gonadotropins (75 to 450 IU) starting on cycle day 2 or 3. The GnRHant is started to block the endogenous LH surge when the lead follicular diameter reaches 14 mm or on the sixth day of ovarian stimulation. When at least three follicles reach, 18 mm hCG is administered.

The minimal stimulation protocol utilizes clomiphene citrate, a selective estrogen receptor modulator (SERM), or letrozole, an aromatase inhibitor, with or without gonadotropins. When decreasing or eliminating gonadotropin stimulation, the cost to the couple is reduced. The minimal stimulation protocol is gaining more support as studies have found that while the live birth rate is slightly decreased compared to the long GnRHa protocol (49% vs. 63%), there are significantly lower rates of ovarian hyperstimulation syndrome and multiple pregnancies.[12][13]

Oocyte Retrieval

Regardless of the stimulation protocol, mature oocytes are retrieved 34 to 36 hours after hCG administration. Oocyte retrieval is performed using ultrasound-guided transvaginal aspiration and intravenous sedation. The ovaries are visualized using a vaginal ultrasound probe, and an attached needle guide helps the physician direct the needle into each follicle and aspirate the oocyte and follicular fluid.

Embryo Fertilization

Insemination or ICSI is used to fertilize the oocytes. The semen sample is prepared by isolating the sperm by density centrifugation and washing it in media with a high protein concentration to promote capacitation, a process that is necessary for sperm to become fertilizable. Fifty to one hundred thousand sperm are incubated with an oocyte for 12-18 hours. Male factor infertility may require ICSI, where one immobilized sperm is directly injected into the oocyte. This bypasses the need for the sperm to penetrate the zona pellucida, the glycoprotein matrix that surrounds the oocyte.

Embryo Transfer

Fertilized embryos are transferred at the cleavage stage (3 days after fertilization) or the blastocyst stage (5 days after fertilization). The blastocyst stage transfer offers higher live births per cycle and is achieved with fewer embryo numbers and thus lower multiple gestation rates.[14] However, the downside of the blastocyst stage transfer is that fewer embryos may be available for transfer due to the loss of embryos that did not survive in culture until day 5.

Embryos are transferred under transabdominal ultrasound guidance into the uterus by a catheter passing thru the cervix. The embryo(s) are placed 1 to 2 cm from the uterine fundus. After the transfer, the catheter is checked under the microscope to ensure no embryos are retained in the catheter and that all embryos were successfully placed in the uterus. The number of embryos transferred will depend on the embryo stage, embryo quality, maternal age, and patient preference. The American Society for Reproductive Medicine recommends no more than two blastocysts to be transferred in women 37 years-old or less, no more than three blastocysts in 38 to 40 year-olds as well as in women 41 to 42 years of age.[15] A higher number of cleavage stage embryos can be transferred due to the lower likelihood of successful implantation; no more than two embryos in women < 35 years of age, no more than three embryos in women 35 to 37 years of age, no more than four embryos in women 38 to 40 and in women 41 to 42 years of age, five or fewer embryos.

To optimize embryo implantation and a continuing pregnancy, progesterone supplementation is initiated on the day of oocyte retrieval or embryo transfer. Excess good quality embryos are cryopreserved for future use.

Complications

Ovarian hyperstimulation syndrome is a potentially life-threatening complication of ovarian stimulation. In mild cases, women experience abdominal distension, nausea, and vomiting. In more severe cases, ascites develop with severe abdominal pain and possible pleural effusion, which may lead to decreased pulmonary function and hypoxia. Patients may show signs of hypovolemia, oliguria, elevated creatinine, increased liver transaminases, leukocytosis, and electrolyte abnormalities. Hemoconcentration will increase the risk of thromboembolism. In critical cases, acute renal failure and disseminated intravascular coagulation may result in death. The World Health Organization (WHO) estimates the incidence of severe OHSS to be 0.2 to 1% of all stimulation cycles.[16]

The frequency of twins has risen from 1980 to 2015, and it is estimated that 19% of all twins and 25% of all triplets are due to IVF.[17] Given the new ASRM recommendations for limiting the number of transferred embryos, the number of triplets has been declining. Multiple gestations can lead to an increased risk of hypertensive disorders of pregnancy as well as preterm birth. Interestingly, however, the rate of hypertensive disorders in IVF twin pregnancies compared to twins conceived naturally do not differ.[18] 

Similarly, there does not appear to be a significant difference in the rate of preterm birth between IVF twin vs. naturally conceived twin pregnancies, likely due to the higher risk of both hypertension and preterm birth in twin pregnancies in general.[19] One systematic review and meta-analysis found that clear differences emerge when comparing singleton pregnancies. Pandey et al.[20] found that singleton IVF pregnancies are associated with increased risk of hypertensive disorders of pregnancy, preterm delivery, as well as gestational diabetes, antepartum hemorrhage, congenital abnormalities, cesarean sections, low birth weight, small for gestational age, and perinatal mortality.

Clinical Significance

Infertility affects approximately 1 in 8 couples in the United States. Since 1978, over 5 million children worldwide have been conceived via IVF.[2] According to the 2018 Society for Assisted Reproductive Technology, live births rates per intended egg retrieval by age group were as follows (www.sart.org):

Women <35 years:

• Live births - 47.6%
• Singleton (%of live births) - 89.4%
• Twins (%of live births) - 10.4%
• Triplets (%of live births) - 0.2% 

35-37 years:

• Live births - 30.7%
• Singleton (%of live births) - 90.3%
• Twins (%of live births) - 9.5%
• Triplets (%of live births) - 0.2%

38-40 years:

• Live births - 21.7%
• Singleton (%of live births) - 90.9%
• Twins (%of live births) - 8.9%
• Triplets (%of live births) - 0.1% 

41-42 years:

• Live births - 10.4%
• Singleton (%of live births) - 93.6%
• Twins (%of live births) - 6.3%
• Triplets (%of live births) - 0.2% 

>42 years:

• Live births - 3.1%
• Singleton (%of live births) - 94.9%
• Twins (%of live births) - 5.1%
• Triplets (%of live births) - 0%

Enhancing Healthcare Team Outcomes

Reproductive endocrinology and infertility as a field are highly interdisciplinary. It requires a team consisting of physicians, nurses, embryologists, and other personnel in order to provide successful treatment to patients. Good communication among staff and patients are critical in helping the patient navigate the complexities of IVF treatment. Furthermore, it is important to note the increased psychological stress that many patients face when going through IVF. Patients often do not have adequate emotional support from their close social contacts, and research suggests such lack of support leads to lower conception rates and one of the main reasons for attrition from IVF treatment.[21] It is, therefore, critical that all members of the treatment team take the time to have open lines of communication with the patients and provide patient-centered care.