Assisted conception. I—General principlesBMJ 2003; 327 doi: https://doi.org/10.1136/bmj.327.7418.799 (Published 02 October 2003) Cite this as: BMJ 2003;327:799
- Paula Rowell, senior embryologist,
- Peter Braude
Although many assisted conception technologies exist—and have a bewildering array of acronyms—their principal aim is similar. They all aim to bring sperm and the egg close to each other to promote the chances of fertilisation and, ultimately, achieve a pregnancy.
The three main types of assisted conception are intrauterine insemination, in vitro fertilisation, and intracytoplasmic sperm injection.
Intrauterine insemination—Prepared sperm are deposited in the uterus at a time when ovulation is likely or assisted
In vitro fertilisation—Fertilisation is aided by mixing eggs and sperm in the laboratory
Intracytoplasmic sperm injection—A single sperm is injected directly into the egg cytoplasm to achieve fertilisation.
Each of these assisted conception techniques requires three procedures: pharmacological stimulation of the ovary to promote the production of more than one egg (superovulation); laboratory preparation of the semen sample to yield a highly motile, morphologically normal population of sperm for insemination or injection (sperm preparation); and techniques to aid the union of sperm and egg (assisted fertilisation).
Multifollicular development can be achieved by using oral antioestrogens, such as clomifene citrate or tamoxifen. However, more often multifollicular development requires injected preparations containing the pituitary hormone, follicle stimulating hormone (FSH).
FSH used to be obtained from extracts of urine collected from postmenopausal women, which were then purified to various degrees to remove contaminating proteins and luteinising hormone. The extracts provided a preparation of human menopausal gonadotrophins marketed as human menotropins—for example, Merional, Menogon, Menopur. Variation within batches of gonadotrophins, and the increasing unacceptability of injecting biologically derived substances, has led to the more widespread use of recombinant products. These include Gonal-F (follitropin α) and Puregon (follitropin β). Although chemically pure, and thus batch consistent, these are more expensive than the equivalent urinary derived products.
The dose of FSH must be titrated carefully to achieve the desired effect on the ovary without side effects or over-response. Cycles may need to be cancelled before insemination if there is a risk of high order multiple pregnancy. Egg collection should be cancelled if there is a risk of ovarian hyperstimulation syndrome. Better control of cycles may be achieved using gonadotrophin releasing hormone (GnRH) analogues, or antagonists in combination with gonadotrophins. However, GnRH analogues do have side effects such as headaches, hot flushes, vaginal dryness, sweating, mood swings, and depression.
The aim of intrauterine insemination is to provide up to three developing mature follicles. More than three developing follicles would put the patient at risk of a high order multiple pregnancy. For in vitro fertilisation or intracytoplasmic sperm injection the superovulation regimen is more aggressive. These two treatments aim to harvest eggs, fertilise them in vitro then select embryos to be put back in the uterus and freeze any suitable surplus embryos.
The incidence of multiple pregnancy in in vitro fertilisation or intracytoplasmic sperm injection cycles can be controlled by restricting the number of embryos placed in the uterus. In the United Kingdom only two embryos can be transferred, although in certain circumstances three embryos are allowed.
Follicular development under gonadotrophin stimulation is tracked by using vaginal ultrasonography to measure the number and growth of follicles. In some reproductive medicine clinics the rise in serum estradiol concentration is also measured. When the leading follicles have reached around 18 mm, human chorionic gonadotrophin (for example, Pregnyl and Profasi) at a dose of 5000 IU to 10 000 IU is given to mimic the natural surge of luteinising hormone, which induces the final maturation of oocytes.
Semen samples are prepared for assisted conception by selecting for a population of highly motile, morphologically normal sperm and removing the seminal plasma, leucocytes, and bacteria.
Freshly ejaculated sperm cannot fertilise an egg until they have undergone further maturation (capacitation). Capacitation occurs naturally in vivo as motile sperm swim out of seminal fluid and through the female genital tract towards the site of fertilisation in the fallopian tubes. Preparation techniques have been developed that select sperm with fertilising ability and promote capacitation in the test tube.
For intrauterine insemination, the sample of washed, prepared, motile sperm is deposited in the uterus just before the release of an egg or eggs in a natural or a stimulated cycle. The technique is most effective when it is combined with mild superovulation using gonadotrophins. Intrauterine insemination is usually the first step in treating couples with unexplained infertility. It is simpler, cheaper, and less invasive than in vitro fertilisation or intracytoplasmic sperm injection, and it has few complications. The sperm sample is specially prepared as if neat, unwashed semen was injected it could introduce infection or provoke painful uterine contractions in response to seminal prostaglandins. Intracervical insemination of unprepared semen without superovulation is ineffective as a treatment for unexplained infertility.
When superovulation is used, the size and number of follicles are measured using ultrasonography, and a human chorionic gonadotrophin injection is given to simulate the preovulatory rise in luteinising hormone. The prepared sperm sample is concentrated to a small volume (usually 0.2–0.3 ml) and injected in the uterus using a soft catheter at the same time as the human chorionic gonadotrophin injection is given, or up to 24 hours later. The sperm then swim to the fallopian tubes, where fertilisation may occur naturally if a mature oocyte has been released because of stimulation treatment.
Pregnancy rates vary considerably among clinics but are generally around 15% per cycle. Several factors affect the success of intrauterine insemination including cause of infertility, ages of partners, sperm quality, and duration of infertility. Multiple pregnancy is a substantial risk for superovulated intrauterine insemination, and the cycle should be cancelled if there are more than three developing follicles.
In the United Kingdom donor insemination requires a licence from the Human Fertilisation and Embryology Authority (HFEA).
Donors are recruited by sperm banks and are screened for a personal or family history of medical or genetic disorders and sexually transmitted infections including HIV, hepatitis B, and hepatitis C. The donor's blood group and karyotype are tested and a serology test for previous exposure to cytomegalovirus is done. If semen quality is normal, the potential donor should have counselling on the implications before he proceeds. If he does wish to donate, sperm samples are frozen and quarantined pending the results of two further HIV tests three and six months later. If these tests are negative, the sperm can be made available for donor insemination.
For donor insemination, the woman needs to have at least one functioning fallopian tube and she must be ovulatory (or capable of responding to ovulation induction treatment). Insemination is usually done in the same way as intrauterine insemination, by using prepared sperm introduced through the cervix into the uterine cavity just before ovulation. It can be done in natural cycles or in stimulation cycles in which ovulation is induced by clomifene or gonadotrophins. The average live birth rate per cycle is about 10%, but it is influenced by the age of the woman. Most reproductive medicine units strongly recommend counselling for couples seeking donor insemination. Counselling ensures that both partners have the chance to explore all the issues related to the use of donor gametes. Under the regulations of the HFEA only 10 pregnancies can result from one donor.
Gamete intrafallopian transfer
Gamete intrafallopian transfer is a laparoscopic technique in which eggs and sperm are placed directly in the ampullary portion of the fallopian tube, allowing in vivo fertilisation to occur at the natural site. Gamete intrafallopian transfer can be used only in women who have at least one patent fallopian tube.
In common with in vitro fertilisation, a gamete intrafallopian transfer cycle begins with superovulation to recruit multiple follicles and is followed by egg retrieval. Egg retrieval may be done transvaginally (with guidance from ultrasonography). Alternatively, the gametes can be replaced in the tube using a laparoscopic procedure in which the patient is under general anaesthesia. The fallopian tube is cannulated with a catheter containing no more than 60 µl of fluid, which has eggs and sperm in it. The semen sample is prepared before surgery, and a small sperm aliquot containing 100 000–200 000 motile sperm is used.
In centres licensed by the HFEA only three oocytes may be transferred to the fallopian tube with the sperm sample, but two oocytes are more appropriate in young patients. Gamete intrafallopian transfer is not a licensed treatment under the Human Fertilisation and Embryology Act and therefore is not under the control of the HFEA. When gamete intrafallopian transfer is offered in units that are not licensed by the HFEA, there is no regulation of the number of oocytes replaced.
With the simplification of in vitro fertilisation and an increase in its success, gamete intrafallopian transfer offers little clinical advantage. Indeed, the need for general anaesthesia and laparoscopy is a distinct disadvantage. Gamete intrafallopian transfer is used rarely in the United Kingdom now, but more often in countries where there are no or few restrictions on the number of oocytes that can be transferred, or where in vitro fertilisation is less successful.
First proposed in 1984, gamete intrafallopian transfer may be seen by patients as more “natural” than in vitro fertilisation, even though it requires laparoscopy and has an increased risk of multiple pregnancy. Gamete intrafallopian transfer is also deemed more acceptable in some religious circles because fertilisation occurs within the body rather than in a laboratory and surplus embryos need not be created
The ABC of subfertility is edited by Peter Braude, professor and head of department of women's health, Guy's, King's, and St Thomas's School of Medicine, London, and Alison Taylor, consultant in reproductive medicine and director of the Guy's and St Thomas's assisted conception unit. The series will be published as a book in the winter.
Competing interests None declared.