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In vitro fertilisation (FIVET)

letto 7693 volte | autore: Claudio Manna, ginecologo specialista in fecondazione assistita (vai al curriculum)

         

In vitro fertilisation and embryo transfer.

As indicated by the name, FIVET makes it possible for ovules and the spermatozoa meet outside the uterus and control fertilisation. The woman undergoes hormonal treatment that favours the maturation of  many ovules simultaneously, and the man supplies the spermatozoa.  The ovules are harvested and put in a container of culture with the spermatozoa and the fertilisation of many ovules is observed with a microscope.  Three days after harvesting, the embryos’ are re-emitted into the uterus, normally in quantities of about 2-3 to increase the probability that at least one will result in pregnancy.  This method is successful about 25% of the time.

FIVET: why and for whom?
The first birth by in vitro fertilisation was by  English, Louise Brown in 1978, since then about 50.000 children have been born from FIVET.  In human beings natural fertilisation takes place inside the fallopian tubes after sexual intercourse during the ovulatory period; however for fertilisation to take place a large number of mobile spermatozoa capable of travelling from the uterus to the tubes is required, and these have to be perfectly functional and open in order to capture the ova when ovulation takes place.  The inside of the fallopian tube is made of tissue that makes small movements that allow the ova to move along its surface until they meet the spermatozoa, in fact, unlike the latter, the ova is not capable of moving on its own.  After fertilisation, movements of the tubes move the young embryo towards the uterine cavity where it will be permanently implanted after about a week.

A complicated process
The complicated and sophisticated reproductive mechanisms can be damaged by many pathologies.  Initially FIVET was put in place to allow women without tubes to conceive.  The idea was simple, organise the ova-spermatozoa meeting in the laboratory (in vitro) and support fertilisation this way, then transfer the embryo into the uterus.  From 1978, the year of the birth of the first test tube baby, the reasons for FIVET have continued to grow and they are no longer limited to tubal abnormalities.  The women who resort to classical FIVET, that is  without the micro-injection of the spermatozoa (ICSI), present with tubal abnormalities only 50% of the time.  The causes of these abnormalities are diverse: previous genital infections, post surgical adhesions, extra-uterine pregnancies…. in one third of these cases an alteration of the mans sperm is involved.  In fact abnormalities of the spermiogram alone are sufficient to direct towards classical FIVET in 20% of the cases, even when the tubes are perfectly healthy.  Other reasons for FIVET are endometriosis – a disease characterised by the presence of abnormal mucus in the peritoneo and in the ovaries – and unexplainable cases of infertility.  In this last case the resorting to FIVET happens after many fruitless attempts at simple ovarian stimulation and intra uterine insemination.

Methods and results
Generally simple ovarian stimulation can have 10-20% success rate per cycle, intrauterine insemination about 10-15%.  FIVET and ICSI yield an average of about 25% pregnancy rate per attempt.

How many spermatozoa?
Artificial insemination: 500.000 mobile spermatozoa
In vitro fertilisation: 2-300.000 mobile spermatozoa
Micro-injection (ICSI): 1 spermatozoon

FIVET: how does it work
Complicated to explain, FIVET seems easy because it “simply” consists of, recreating in a laboratory, in a test tube with special cultures, what happens during fertilisation in the woman’s tubes. The three stages of FIVET are: the harvesting of  the male and female sex cells (gametes), fertilisation and transfer of the embryo.

The gametes: ova, the female sex cells      
Found in the follicles, the ova are stored in the ovaries of  the future mother from birth, their development is blocked until puberty.  Starting from this moment in women of child bearing age only sex cell matures per menstrual cycle.  Every month an ovum completes its cellular maturation inside the follicle and is expelled by the ovary, mean while the growth of other follicles, which will have recommenced their development at the same time is arrested and they die.  The greater part of FIVET is realised starting with a stimulated cycle in order to obtain as many ova as possible and therefore increase the possibility of pregnancy.  Now, lets speak about multi-follicular stimulation.  This type of stimulation.  This type of stimulation entails the use of hormones that guarantee that one side of the ovaries is “put to rest”. Their desensitisation  can this way increase the number of follicles recruited, and the stimulation of their growth. Apart from the daily injections for a period varying from 2-3 weeks, this sort of stimulation requires very strict monitoring based on  the results of constant ovarian ultrasounds and of the hormonal dosages.  Referred to  as “monitoring” this allows that as many follicles as possible be brought to maturity and also helps to prevent over stimulation or hyper-stimulation which could have very serious consequences for the woman.  When the follicles have reached the right dimension an injection of human chorionic gonadotropine triggers ovulation allowing the ova contained in each follicle to reach maturity.  Thirty six hours after the injection the ovarian follicles, which now have a dimension of about 15-20mm are retrieved, an operation that generally takes place under local anaesthetic and consists in the aspiration of the liquid in the follicle via a needle guided by an ultrasound probe situated in the vagina.  The biologist can therefore look for mature ova necessary for fertilisation.                          

The gametes: spermatozoa, the male sex cells
To obtain spermatozoa from a man generally poses less problems because their production is constant, commencing from the age of puberty and there are millions in every ejaculation.  Practically, the man is required to abstain from sex for three days before FIVET, in order to obtain good quality sperm.  The harvest of the sperm generally happens on the same day as FIVET, through masturbation undertaken in the medical centre.  In particular cases, if the spermatozoa cannot be emitted because of an obstruction of one of the tubes, they have to extract the spermatozoa by way of a testicular biopsy on the same day as FIVET or some time before in which case they are frozen.

Insemination and fertilisation
The biologist prepares the gametes in the laboratory: the seminal liquid is collected and washed and the biologist selects the most mobile spermatozoa and allows the champions to warm up in a special place; the ova are extracted from the follicular liquid and isolated.  Each ovum is then placed in a culture  together  with the most mobile spermatozoa, between 10.000 and 100.000 per ovum, depending on the technique to be used.  This is the stage which is different in ICSI.  The containers of culture are placed in an incubator at 37° C and already after 24 hours it is possible to see the number of ova that have been fertilised.  In the following 24 hours, that is 48 hours after the extraction of the ova the number of embryos obtained is known.

Transfer of the embryos
Two days after the extraction of the ova the embryos are made up of an average of about four cells called blastomere. At this point they can be transferred into the uterine cavity.  They can also remain in culture for an additional four days, this allowing for a better selection of the embryos to take place and indirectly increasing the probability of pregnancy.  In special situations it is necessary to leave the embryos for longer in order to conduct pre-implant diagnosis.  These days in a large number of cases two embryos are transferred, painlessly, using a very fine plastic tube inserted into the neck of the uterus the embryos are pushed into the uterine cavity with an ordinary syringe and a small quantity of follicular liquid.  After about 12 days a pregnancy test is performed.  Any  extra embryos produced can be frozen, this decision is, however, left to the couple.

The results of FIVET
The recourse to the intracytoplasmic micro-injection of one spermatozoon (ICSI) is more and more frequent.  The percentage of pregnancies per transfer, identical in the case of FIVET to ICSI,  reaches about 25%.  If a woman undergoes embryo transfer, statistically she has one in four chances of  falling pregnant, even though it is important to say that this varies a lot depending on different factors.  In the case of ICSI the probability of success is higher if the abnormality involves only the sperm and not endometriosis.  One of the principal prognostic elements is the age of the woman at the moment of FIVET, given that the percentage of pregnancies by aspiration remains relatively stable until the age of  37 (>25%) but then rapidly decreases to 17% at age 40 and only 10% at age 42.  The number of embryos transferred also influences the success rate, because the probabilities of pregnancy are about 10% after the transfer of one embryo but more than 30% after the transfer of three embryos, even though this increases the risk of multiple pregnancies.  The probability of twin pregnancies is about 20% with the transfer of two embryos and more than 30% with the transfer of three embryos even though the probability of success does not increase by transferring more than three embryos, the percentage of multiple pregnancies decreases (15% of triplet pregnancies with the transfer of 6 embryos).  These statistics explain why FIVET centres limit transfer to a maximum of 2 or 3 embryos and the transfer of four or more embryos regards only 10% of the cases.

In vitro Fertilisation

Disclaimer: the information provided on this site is designed to support, not replace, the relationship that exists between a patient/site visitor and his/her existing physician.

venerdì 21 marzo 2008


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