In vitro fertilization (IVF)

 

In vitro fertilization (IVF) is a process by which egg cells are fertilized by sperm outside the womb, in vitro. IVF is a major treatment in infertility when other methods of assisted reproductive technology have failed. The process involves hormonally controlling the ovulatory process, removing ova (eggs) from the woman's ovaries and letting sperm fertilize them in a fluid medium. The fertilized egg (zygote) is then transferred to the patient's uterus with the intent to establish a successful pregnancy. The first "test tube baby", Louise Brown, was born in 1978.

Indications

IVF may be used to overcome female infertility in the woman due to problems of the fallopian tube, making fertilization in vivo difficult. It may also assist in male infertility, where there is defect sperm quality, and in such cases intracytoplasmic sperm injection (ICSI) may be used, where a sperm cell is injected directly into the egg cell. This is used when sperm have difficulty penetrating the egg, and in these cases the partner's or a donor's sperm may be used. ICSI is also used when sperm numbers are very low. ICSI results in success rates equal to those of IVF fertilization.

For IVF to be successful it may be easier to say that it requires healthy ova, sperm that can fertilize using ICSI, and a uterus that can maintain a pregnancy. Due to the costs of the ICSI procedure, IVF is generally attempted only after less expensive options have failed.

ICSI also avails for egg donation or surrogacy where the woman providing the egg isn't the same who will carry the pregnancy to term. This means that IVF can be used for females who have already gone through menopause. The donated oocyte can be fertilized in a crucible. If the fertilization is successful, the zygote will be transferred into the uterus, within which it will develop into an embryo.

IVF can also be combined with preimplantation genetic diagnosis (PGD) to rule out presence of genetic disorders. A similar but more general test has been developed called Preimplantation Genetic Haplotyping (PGH).


Methods

Ovarian stimulation

Treatment cycles are typically started on the third day of menstruation and consist of a regimen of fertility medications to stimulate the development of multiple follicles of the ovaries. In most patients injectable gonadotropins (usually FSH analogues) are used under close monitoring. Such monitoring frequently checks the estradiol level and, by means of gynecologic ultrasonography, follicular growth. Typically approximately 10 days of injections will be necessary. Spontaneous ovulation during the cycle is typically prevented by the use of GnRH antagonists, which block the natural surge of luteinizing hormone (LH).

Transvaginal oocyte retrieval

When follicular maturation is judged to be adequate, human chorionic gonadotropin (hCG) is given. This agent, which acts as an analogue of luteinizing hormone, would cause ovulation about 42 hours after injection, but a retrieval procedure takes place just prior to that, in order to recover the egg cells from the ovary. The eggs are retrieved from the patient using a transvaginal technique involving an ultrasound-guided needle piercing the vaginal wall to reach the ovaries. Through this needle follicles can be aspirated, and the follicular fluid is handed to the IVF laboratory to identify ova. It is common to remove between ten and thirty eggs. The retrieval procedure takes about 20 minutes and is usually done under conscious sedation or general anesthesia.

Fertilization

In the IVF laboratory, the identified eggs are stripped of surrounding cells and prepared for ICSI fertilization. In the meantime, semen is prepared for fertilization by removing inactive cells and seminal fluid. If semen is being provided by a sperm donor, it will usually have been prepared for treatment before being frozen and quarantined, and it will be thawed ready for use. The sperm and the egg are incubated together at a ratio of about 75,000:1 in the culture media for about 18 hours. In most cases, the egg will be fertilized by that time and the fertilized egg will show two pronuclei. In certain situations, such as low sperm count or motility, a single sperm may be injected directly into the egg using intracytoplasmic sperm injection (ICSI). The fertilized egg is passed to a special growth medium and left for about 48 hours until the egg consists of six to eight cells.

In gamete intrafallopian transfer, eggs are removed from the woman and placed in one of the fallopian tubes, along with the man's sperm. This allows fertilization to take place inside the woman's body. Therefore, this variation is actually an in vivo fertilization, not an in vitro fertilization.

Selection

Laboratories have developed grading methods to judge oocyte and embryo quality. Typically, embryos that have reached the 6-8 cell stage are transferred three days after retrieval. In many American and Australian and Ukrainian programs, however, embryos are placed into an extended culture system with a transfer done at the blastocyst stage at around five days after retrieval, especially if many good-quality embryos are still available on day 3. Blastocyst stage transfers have been shown to result in higher pregnancy rates. In Europe, transfers after 2 days are common. Preimplantation Genetic Diagnosis (PGD) procedures may be performed prior to transfer.

Embryo transfer

Embryos are graded by the embryologist based on the number of cells, evenness of growth and degree of fragmentation. The number to be transferred depends on the number available, the age of the woman and other health and diagnostic factors. In countries such as the UK, Australia and New Zealand, a maximum of two embryos are transferred except in unusual circumstances. In the UK and according to HFEA regulations, a woman over 40 may have up to three embryos transferred, whereas in the USA, younger women may have many embryos transferred based on individual fertility diagnosis. Most clinics and country regulatory bodies seek to minimize the risk of pregnancies carrying multiples. The embryos judged to be the "best" are transferred to the patient's uterus through a thin, plastic catheter, which goes through her vagina and cervix. Several embryos may be passed into the uterus to improve chances of implantation and pregnancy. 

Pregnancy rates

Pregnancy rate is the success rate for pregnancy. For IVF, it is the percentage of all attempts that lead to pregnancy, which generally refers to treatment cycles where eggs are retrieved and fertilized in vitro (using ICSI or not). Statistics referring to "pregnancy" may refer to just a positive pregnancy test, and not necessarily "viable pregnancy" which implies the detection of a fetal heart beat. Pregnancies that are delivered with a viable baby are called live birth rate. Increasingly a distinction is also made between singleton and multiple pregnancies as multiple pregnancies, specifically more than twins, should be avoided because of the associated maternal and fetal risks.

With enhanced technology, the pregnancy rates are substantially better today than a couple of years ago. In 2006, Canadian clinics reported an average pregnancy rate of 35%. A French study estimated that 66% of patients starting IVF treatment finally succeed in having a child (40% during the IVF treatment at the center and 26% after IVF discontinuation). Achievement of having a child after IVF discontinuation was mainly due to adoption (46%) or spontaneous pregnancy (42%).

Effect of stress

In a 2005 Swedish study, 166 women were monitored starting one month before their IVF cycles (including ICSI cases), and the results showed no significant correlation between psychological stress and IVF outcome. The study concluded with the recommendation to clinics that it might be possible to reduce the stress experienced by IVF patients during the treatment procedure by informing them of those findings. While psychological stress experienced during a cycle might not influence an IVF outcome, it is possible that the experience of IVF can result in stress that leads to depression. The financial consequences alone of IVF can influence anxiety and become overwhelming. However, for many couples, the alternative is infertility, and the experience of infertility itself can also cause extreme stress and depression.

Live birth rate

Live birth rate is the percentage of all IVF cycles that lead to live birth, and is the pregnancy rate adjusted for miscarriage and stillbirth. These percentages are for successful pregnancies, regardless of the number of children born, as twins and larger multiple-order births are more common in IVF cycles.

In 2006, Canadian clinics reported a live birth rate of 27%. A summary of 2006 reports from US clinics for cycles that did not involve donor eggs gave success rates varied widely by the age of the prospective mother, with a peak at 42.6% for 27-year-olds. Rates for younger patients were slightly lower, with a success rate of 35.3% for those 21 and younger, the youngest group evaluated. Success rates for older patients were also lower and decrease with age, with 37-year-olds at 27.4% and no live births for those older than 48, the oldest group evaluated. IVF attempts in multiple cycles result in increased cumulative live birth rates. Depending on the demographic group, one study reported 45% to 53% for three attempts, and 51% to 71% for six attempts. 

Complications

The major complication of IVF is the risk of multiple births. This is directly related to the practice of transferring multiple embryos at embryo transfer. Multiple births are related to increased risk of pregnancy loss, obstetrical complications, prematurity, and neonatal morbidity with the potential for long term damage. Strict limits on the number of embryos that may be transferred have been enacted in some countries (e.g. England) to reduce the risk of high-order multiples (triplets or more), but are not universally followed or accepted. Spontaneous splitting of embryos in the womb after transfer can occur, but this is rare and would lead to identical twins. A double blind, randomized study followed IVF pregnancies that resulted in 73 infants (33 boys and 40 girls) and reported that 8.7% of singleton infants and 54.2% of twins had a birth weight of < 2500 g. However recent evidence suggest that singleton offspring after IVF is at higher risk for lower birth weight for unknown reasons.

Another risk of ovarian stimulation is the development of ovarian hyperstimulation syndrome.

If the underlying infertility is related to abnormalities in spermatogenesis, it is plausible, but too early to examine that male offspring is at higher risk for sperm abnormalities.

Birth defects

The issue of birth defects has been a controversial topic in IVF. Many studies do not show a significant increase after use of IVF, and some studies suggest higher rates for ICSI, whereas others do not support this finding. In 2008, an analysis of the data of the National Birth Defects Study in the US found that certain birth defects were significantly more common in infants conceived with IVF, notably septal heart defects, cleft lip with or without cleft palate, esophageal atresia, and anorectal atresia; the mechanism of causality is unclear.

Japan's government prohibited the use of in vitro fertilization procedures for couples in which both partners are infected with HIV. Despite the fact that the ethics committees previously allowed the Ogikubo Hospital, located in Tokyo, to use in vitro fertilization for couples with HIV, the Health, Labour and Welfare Ministry of Japan decided to block the practice. Hideji Hanabusa, the vice president of the Ogikubo Hospital, states that together with his colleagues, he managed to develop a method through which scientists are able to remove the AIDS virus from sperm.

Embryo cryopreservation

The first pregnancy derived from a frozen human embryo was reported by Alan Trounson & Linda Mohr in 1983 (although the fetus aborted spontaneously at about 20 weeks of gestation); the first term pregnancies derived from frozen human embryos were reported by Zeilmaker et al. and the first human baby hatched via a rate frozen freezing process was born in 1984. Since then and up to 2008 it is estimated that between 350,000 and half a million IVF babies have been born from embryos controlled rate frozen and then stored in liquid nitrogen; additionally a few hundred births have been born from vitrified oocytes but firm figures are hard to come by.

On the safety of embryo cryopreservation, a 2008 study reported at the European Society of Human Reproduction and Embryology discovered that children born from frozen embryos did “better and had a higher birth weight” than children born from a fresh transfer. The study was conducted out of Copenhagen and evaluated babies born during the years 1995–2006. 1267 children born after Frozen Embryo Replacement (FER), via controlled-rate freezers and storage in liquid nitrogen, were studied and categorized into three groups. 878 of them were born using frozen embryos that were created using standard in vitro fertilization in which the sperm were placed into a dish close to the egg but had to penetrate the egg on their own. 310 children were born with frozen embryos created using ICSI in which a single sperm was injected into a single egg, and 79 were born where the method of creation of the embryos was not known.

17,857 babies born after a normal IVF/ICSI with fresh embryos were also studied and used as a control group or reference group. Data on all of the children’s outcomes were taken regarding birth defects, birth weights, and length of pregnancy. The results of the study showed that the children who came from frozen embryos had higher birth weights, gave longer pregnancies and produced fewer “pre-term” births. There was no difference in the rate of birth defects whether the children came from frozen embryos or fresh embryos. In the FER group, the birth defect rate was 7.7% compared to the fresh transfer group which was slightly higher at 8.8%. The scientists also found that the risk for multiple pregnancies was increased in the fresh embryo transfers.

Around 11.7% of the ICSI and 14.2% of the IVF frozen cases were multiple pregnancies. In the case of fresh embryos, 24.8% of the ICSI and 27.3% of the IVF were multiple pregnancies. It should also be noted that maternal age was significantly higher in the FER group. This is significant since based on age one would have expected a higher rate of problems and birth defects. The study adds to the body of knowledge suggesting that traditional embryo freezing is a safe procedure. It was unclear however why the frozen embryo children did better than their fresh embryo counterparts

If multiple embryos are generated, patients may choose to freeze embryos that are not transferred. Those embryos are slow frozen and then placed in liquid nitrogen and can be preserved for a long time. The advantage is that patients who fail to conceive may become pregnant using such embryos without having to go through a full IVF cycle. Or, if pregnancy occurred, they could return later for another pregnancy. Spare embryos resulting from fertility treatments may be donated to another woman or couple, and embryos may be created, frozen and stored specifically for transfer and donation by using donor eggs and sperm.

Oocyte cryopreservation

Cryopreservation of unfertilized mature oocytes has been successfully accomplished, e.g. in women who are likely to lose their ovarian reserve due to undergoing chemotherapy. The rate of thaw leading to successful pregnancies is still very low.

Embryo donation and Egg donor

There may be leftover embryos or eggs from IVF procedures if the woman for whom they were originally created has successfully carried one or more pregnancies to term. With the woman's or couple's permission, these may be donated to help other women or couples as a means of third party reproduction.

In embryo donation, these extra embryos are given to other couples or women for transfer with the goal of producing a successful pregnancy. The resulting child is considered the child of the woman who carries it and gives birth, and not the child of the donor, the same as occurs with egg donation or sperm donation.

Typically, genetic parents donate the eggs to a fertility clinic or embryo bank where they are cryogenically preserved until a carrier is found for them. Typically the process of matching the embryo(s) with the prospective parents is conducted by the agency itself, at which time the clinic transfers ownership of the embryos to the prospective parents. 

The amount of screening the embryo has already undergone is largely dependent on the genetic parents' own IVF clinic and process. The embryo recipient may elect to have her own embryologist conduct further testing.

Alternatives to donating unused embryos are discarding them (or having them implanted at a time where pregnancy is very unlikely), keeping them frozen indefinitely, donating them for use in embryonic stem cell research.

Acupuncture

An increasing number of fertility specialists and centers offer acupuncture as a part of their IVF protocol. Limited but supportive evidence from clinical trials and case series suggests that acupuncture may improve the success rate of IVF and the quality of life of patients undergoing IVF and that it is a safe adjunct therapy. A systematic review and meta-analysis published in the British Medical Journal found that complementing the embryo transfer process with acupuncture was associated with significant and clinically relevant improvements in clinical pregnancy (where the expected number of patients needed to be treated to produce 1 additional pregnancy was 10), ongoing pregnancy (NNT 9), and live birth (NNT 9).

Acupuncture Mechanisms

Four mechanisms by which it has been suggested that acupuncture may improve IVF outcomes are

  • Neuroendocrinological modulations
  • Increased blood flow to uterus and ovaries
  • Modulation in cytokines
  • Reduction of stress, anxiety, and depression

Treatment success versus the risk of multiple pregnancie

 In order for a woman over age 35 to maximize her chances of conceiving with her own eggs and carrying a healthy pregnancy, she must have more embryos transferred than do younger women. This practice, though, increases her risk of conceiving multiple fetuses.

Because of the risks of multiple pregnancy to the babies, the American Society for Reproductive Medicine recommends that women under age 35 have no more than two embryos transferred, women age 35 to 37 have no more than three, women 38 to 40 have no more than four transferred, and women who have had repeated failed cycles or are over age 40 have no more than five embryos transferred.

Women over 40 have a high rate of embryo loss when they use their own eggs. As an alternative, older women can choose to use more viable donor eggs.