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Sunday, 24 August 2014

Assisted Hatching

Human eggs have a shell all around. This shell is called Zona Pellucida or just Zona in short. The function of the zona is to protect the embryo and to maintain its integrity (by keeping all cells of the embryo together). The function of zona ends when it is time for implantation. An embryo has to hatch out this very shell at the blastocyst stage, otherwise pregnancy will not occur.

Assisted Hatching is a technique which is used to either make a hole in the zona. The thought is to 'assist' an embryo which may either have a thicker zona or lesser ability to make a hole in the zona. 

There are three methods of Assisted hatching: 

  • Mechanical (in which the zona is tangentially pierced with a special needle)
  • Chemical (in which a chemical is delivered to a limited area of the zona to make a hole, the extra chemical is then removed to prevent the chemical from damaging the cells of the embryo)
  • Lasers (where energy from laser is used to make a very controlled breach in the zona)

Assisted hatching is generally applied to Day 3 embryos but can also be applied to Blastocysts to increase implantation rates. 
The current opinion with regard to the use of Assisted Hatching is that this technique can be offered to couples with previous implantation failures, and may improve the pregnancy rates in patients undergoing thawed embryo transfer. It is not clear whether it is beneficial for patients of advanced age. It is not without risks and therefore not recommended for routine use.

Sunday, 3 August 2014

Blastocyst or Freezing?

The ultimate aim of assisted reproductive techniques is not a positive pregnancy test, but a healthy fully grown baby. Advances in the stimulation protocols and embryo culture media have led to an improved ability to grow and select embryos. Despite this, only about 30% of the transferred embryos reach their full developmental potential.

To overcome the low implantation rates, the initial strategy that was employed was to increase the number of embryos. However, this led to an unacceptable incidence of higher order multiple pregnancy with associated complications both to the pregnant mother and to the babies. In a conscious effort to reduce multiple pregnancy, the embryo numbers are therefore restricted. To enable this without affecting the chances of success, there are broadly two options.

The first option is that of embryo freezing. Once a select number of embryos is transferred, the supernumerary embryos are frozen for later use. The newer more efficient technique of Vitrification has further improved cumulative pregnancy rates with frozen embryos. Using this you can actually try transferring all the good embryos a few at a time without the risk of higher order multiple pregnancy. This can also allow the conception of siblings if the initial transfer is successful. 

The second option is to grow the embryos to the blastocyst stage. By extended culture and selecting the best one or at the most two blastocysts, better pregnancy rates can be achieved without increasing the number of embryos that are transferred. The drawback with this option is that only 40-50% of embryos reach blastocyst stage. The biggest advantage is that multiple embryo transfers can be avoided. Most women I know find the two-week wait the most trying period in any treatment cycle. Occasionally, you may be lucky to get supernumerary good quality blastocysts that can be frozen for later use. 

In short both options are good options and decision should be taken collectively keeping in mind the embryo parameters as well as the couple's preference.