If you are either a surrogate or an intended parent pursuing the surrogacy process and/or egg donation for family building, the term PGD may come up. PGD stands for preimplimtation genetic diagnosis, sometimes referred to as embryo screening, and this reproductive technology is used with an in-vitro fertilization (IVF) cycle to diagnose genetic diseases in early embryos prior to implantation into the surrogate mother. You may have also heard of the term preimplantation genetic screening (PGS), which doesn’t look for specific diseases, but uses PGD techniques to identify at-risk embryos. The PGD procedure is extremely helpful when screening for genetic disorders like Down syndrome, muscular dystrophy, cystic fibrosis, Tay Sachs, and sickle cell anemia, although it is not limited to these defects.
Who is a candidate for PGD?
There are several categories of intended parents that should consider PGD:
-The Intended Parents have ended previous pregnancies because of a serious genetic condition.
-The Intended Parents already have a child with a serious genetic condition.
-The Intended Parents have a family history of a serious genetic condition; or
-One or both of the Intended Parents have a family history of chromosome problems.
How is the PGD Procedure Done?
The procedure for PGD is usually as follows:
Step 1. You undergo normal in vitro fertilization (IVF) treatment to collect and fertilize your eggs.
Step 2. The embryo is grown in the laboratory for two to three days until the cells have divided and the embryo consists of around 4-12 cells. (Typically this takes about three days.)
Step 3. A trained embryologist removes one or two of the cells (blastomeres) from the embryo.
Step 4. The cells are tested to see if the embryo from which they were removed contains the gene that causes the genetic condition in the family. Every doctor’s office has their own method of tracking the embryo to the one or two cells that was removed from it. Clearly each embryo biopsied and the removed cell(s) must be carefully tracked so that if a defect is detected the correct embryo is identified.
Step 5. The embryo unaffected by the condition is transferred to the womb 4-5 days following the egg retrieval, to allow it to develop into a pregnancy.
Step 6. Any remaining unaffected embryos can be frozen for later use. Those embryos that are affected by the condition are allowed to perish or, with your consent, used for research.
The Option of a Trophectoderm Biopsy
Recently, trophectoderm biopsy is gaining popularity as an alternative method of embryo biopsy, whereby it is possible to allow an embryo to develop for 5-6 days. 100-150 cells develop for harvesting, instead of removing and testing one or two cells from a two to three-day-old embryo. Trophectoderm cell removal is much less traumatic compared to blastomere removal.
With trophectoderm biopsy, cells within an embryo separate into two types: cells which will form the fetus (inner cell mass) and cells which will form the placenta (trophectoderm). The benefit is that more cells can be removed at this stage (about 16-32), as the trophectoderm is beginning to herniate through the zona pellucida, without compromising the viability of the embryo, possibly leading to a more accurate test. Instead of removing individual blastomeres, several trophectoderm cells are removed.
What are the Risks Associated with PGD in the Surrogate Process?
The techniques used to biopsy are generally thought to be safe with little risk to the embryo. The risk of accidental damage to the embryo during biopsy is typically thought to be approximately 1%. (Some embryologists have stated that their risk factor is less than 1%) There is a slightly lower likelihood of implantation after an embryo biopsy compared to an embryo not having been biopsied. (This remains debatable because so many factors need to be taken into consideration when identifying why an implanted embryos did not result in a pregnancy)
Since PGD is a relatively new technology, other risks may become apparent over time, but to date the risks appear to be quite limited and need to be weighed against the potential benefits for each couple.
PGD and Pregnancy
Some people feel that performing PGD and manipulating the embryo in some way is likely to lessen your chances of a pregnancy through IVF occurring. The PGD procedure is done so early in the development process that it does not affect the chances of pregnancy, or the health of the embryo; however, as with most medical procedure, the success rate depends on the skills of the embryologist involved.
Some doctors even believe that pregnancy success rates actually increase through the use of PGD because only those embryos that have been shown to be in good health are transferred back to the mother. Also, since genetic abnormalities are among the most common reason for a miscarriage, the transferal of embryos that are absent of any abnormalities decreases the risk of another miscarriage.
Should I do PGD with surrogacy?
As with any medical procedure, you should have this discussion with your physician. He or she will determine whether PGD screening is best for you, based on factors of age, fertility history and genetic history of your extended family. Usually, doctors will recommend PGD screening to patients with a history of unexplained infertility and recurrent miscarriages, genetic disease, recurrent miscarriages, unsuccessful IVF cycles, and advanced maternal age.
If you are a potential or existing Surrogate or an Intended Parent through Surrogate Parenting Services and would like to inquire about PGD screening, or you would like to learn more about the surrogate process, contact us at (949) 363-9525.