Lasers, once the weapon of choice for writers of science fiction, then increasingly the everyday tool of the surgeon, have found yet another astonishing role -- as catalysts to aid the very beginnings of life itself.
They are being used for precision drilling the 'shell' of a human egg -- a membrane an average 18 millionths of a metre thick (six times smaller than the smallest object visible to the human eye).
Delegates at the European Society of Human Reproduction and Embryology conference in Bologna, Italy, heard today (Tuesday 27 June) from Hungarian and Belgian fertility experts how lasers are making it easier for embryos to implant in the lining of a woman's womb and turning pre-implantation genetic diagnosis into a quicker, more effective procedure.
Improving pregnancy rates and implantation of embryos in the uterus are the biggest challenges in IVF, according to Dr Katalin Kanyó of the St John Hospital in Budapest, Hungary.
Many IVF failures occur because the fertilised embryo, still encased in its eggshell (a gelatinous protective coat called the zona pellucida), does not manage to embed itself in the lining of the womb. So Dr Kanyó, and colleague Dr Janos Konc, turned to lasers to give the embryo a helping hand. They use an infrared diode laser beam to make a 'tunnel' in the shell immediately before the embryo is transferred to the uterus. Two to three 20-30 millisecond bursts of energy are all that are needed to ensure the embryo's escape and maximise its chance of implantation. From hatching to transferring the embryo to the uterus takes only one minute.
Dr Kanyó told the conference that assisted hatching can be done using mechanical, chemical or laser methods but they were convinced that laser hatching was best. Her technique is novel because the tunnel is made by applying the laser at an angle to the embryo so that only the edge of the beam is in contact with the shell, producing a hole with a diameter between 4.5 and 20 millionths of a metre.
This technique limits the exposure of the embryo to radiation and does not cause any damage to the cell structure or the chromosomes. Another novel feature is that the embryo does not need to be fixed to a holding pipette so the procedure is completed extremely fast.
Lasers helped to achieve 96 confinements at the hospital between December 1998 and December 1999, with 134 live births -- 31 twins, 3 triplets and 63 singletons.
Some European centres, including Budapest, are now using the laser method but Budapest is unique in that the IVF unit followed the babies through pregnancy, using amniocentesis in the fourth month, and undertook physical examinations at birth and after one month.
"We did not find any higher risk of congenital malformation or chromosome abnormalities. Our study shows that lasers provide the quickest, most effective and safest hatching technique," said Dr Kanyó.
The research team concentrated on a special group of women where hatching can increase the pregnancy rate. They were divided into three sections: patients under 35 who had three failed embryo transfers, patients over 35 who had at least three failed IVF attempts and patients over 35 with fewer than three IVF failures or who had no IVF attempts. On average, a third of all the women became pregnant.
Mr Hubert Joris and colleagues from the Centre for Reproductive Medicine in Brussels are using an infrared laser to make a hole in the embryo's shell. Through this hole they retrieve one or two cells from a three day old embryo to test that it is genetically normal before they transfer it to the uterus. This procedure is done specifically for patients at risk for a monogenic disease or chromosomal anomalies.
"We fix the embryo on a holding pipette and move it so the zona is positioned on the exact spot where the laser beam is active and close to the cells we want to aspirate. We provide an energy burst timed according to the thickness of a particular embryo's zona. It usually takes 2 pulses of 11 milliseconds on average to dissolve the zona. The whole procedure is completed in a few seconds."
Mr Joris said that mechanical means for embryo biopsy cause stress to the embryo. There was evidence that acid Tyrode, the chemical most often used, also had a negative impact on the cells immediately exposed to it which could result in losing transferable embryos. His team had compared acid Tyrode with infrared laser. Pregnancy rates were similar for both methods but the laser resulted in significantly more intact cells, crucial for a correct diagnosis at the end of the procedure, and a shorter biopsy time.
Note: Programme numbers: O-156 and O-134
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