Double Joy, Double Trouble?

 

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The occurrence of identical twins after a single embryo transfer

Even after many years of being a doctor, it still brings me immense joy to announce to my patient that she is indeed pregnant following a successful infertility treatment. And sometimes, the happiness is multiplied, as there isn’t one, but two buns in the oven!

 

In general, it is widely known that the occurrence of multiple births is much higher following assisted reproductive technologies (ART) as compared to incidences of twins in natural or spontaneous pregnancies. This is directly related to the number of embryos transferred back to the uterus. In general, if 2 embryos are transferred back into the uterus, the chance of having twin pregnancies is around 20-30%. As we all know, twin pregnancies carries more risks to the expecting mother as well as the babies. The risks of miscarriage, bleeding in pregnancy, high blood pressure, diabetes in pregnancy, Placenta Praevias, Caesarean Sections are some of the significant obstetric risks. The babies are also at risk of preterm births, stillbirths and complications associated with preterm deliveries such as cerebral palsies.

 

Therefore, in many countries especially in the west, it is mandatory that the patients are informed of these risks before an embryo transfer. Some countries had restricted the number of embryos transferred to one. This move had significantly reduce the incidence of twins following an IVF and had reduced the economic burden associated with medical care of pregnancies associated with twins

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However, in recent years, it had been reported that there is a higher incidence of identical twins following single embryo transfer.

 

While the incidence of fraternal twins following the transfer of two embryos is an easily understandable consequence of IVF, the causes for identical twins after ART remain speculative at best. However, there is some evidence that attributes the phenomenon to the micromanipulation techniques, length of culture and culture medium used during treatment, as well as the genetics of the parents.

Identical twins, also known as monozygotic twinning or MZT, occur when an egg and a sperm unite to form a single zygote that divides into two embryos or separate individuals. It is a rare phenomenon, which occurs in only about 1% of natural conceptions. However, in assisted conceptions, the occurrence of monozygotic twinning almost doubles.

 

The splitting of the zygote into separate embryos can occur at any time during the first 2 weeks after fertilisation. However, the timing of the split will influence the type of identical twin. For example, in around 1/3 of MZT cases where the split occurs within 72 hours of fertilisation, the result is two placentas and two amniotic sacs. In the remaining 2/3 of MZT cases, the splitting occurs 4-8 days after fertilisation, resulting in one placenta and two amniotic sacs. And in about 5% of MZT cases, where splitting occurs 8-13 days after fertilisation, the outcome is one placenta and one amniotic sac. In very rare cases, the outcome is conjoined twins.

 

Although the prospect of having twins is certainly exciting, couples must also understand that twin pregnancies are considered high risk. They can lead to various pregnancy complications with long-lasting and even permanent effects for the children. These include caesarean section, premature birth, low birth weight, Twin-Twin Transfusion Syndrome (TTTS), pre-eclampsia, gestational diabetes, fetal abnormalities and congenital abnomalies. In view of the complications that can arise from a twin pregnancy, do speak to your infertility consultant about the risks involved should you have any worries.

 

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What you should know about PGD & PGS

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What you should know about PGD & PGS

If you and your partner have been struggling with fertility issues and are seriously considering In-Vitro Fertilisation or IVF, the consideration of whether you should be undergoing PGD and PGS on top of an IVF can be quite daunting. This is because, in normal IVF procedures, the best embryos are selected based on their appearance and morphology only. Therefore, the genetic content of those embryos or any chromosomal abnormality cannot be detected. However, by undergoing PGD and PGS, you will be able to screen your embryos for any potential genetic and chromosomal issues.  However, before we jump into the band wagon of having PGS or PGD, there are a few things we need to consider.

 

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What is PGS?
PGS stands for Pre-implantation Genetic Screening. In PGS, a cell is taken from an embryo  which was created following an IVF procedure, so that it can be tested for chromosomal abnormalities before the embryo is transferred to the womb. This test will be able to tell us whether the embryo has normal sets of chromosomes. However, it will not be able to tell us whether this embryo has a genetic problem or not.

It is important to note that not all the patients going through an IVF required a PGS. You may want to consider it if:

  • You are of advanced maternal age, whereby embryos may show greater levels of chromosomal abnormalities.
  • You have had recurrent miscarriages.
  • You have had repeated IVF failure.
  • Either of you has a chromosome rearrangement.

The PGS procedure involves:
1. You will undergo a normal IVF treatment and your eggs will be collected and fertilised.
2. An embryo is grown in the laboratory for a few days.
3. An embryologist will perform a biopsy and remove a few cells, usually on day 3 or 5.
4. All 24 chromosomes are analysed (22 non-sex chromosomes and two sex chromosomes X & Y).
5. If the embryo is normal, it will be transferred into your womb.
6. Any remaining unaffected embryos can be frozen for later use.
7. Affected embryos will be allowed to perish.

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What is PGD?
PGD is an abbreviation for Preimplantation Genetic Diagnosis. In PGD, a cell is taken from an IVF embryo so that it can be tested for a specific genetic condition before the embryo is transferred to the womb. It can be used to test for any genetic condition that is known to be caused by a specific gene.

At present, PGD is used to screen for more than 250 genetic conditions, such as Huntington’s disease, Cystic fibrosis, Thalassaemia, Duchenne muscular dystrophy and Fragile-XPDG to name but a few. Therefore, PGD enables individuals with an inheritable genetic condition to avoid passing it on to their children. The PGD process is more tidious and challenging compared to PGS. It is used to test for a specific genetic disease which is known to your family, i.e. you or your partner is confirmed a carrier of a specific gene at a certain point of the chromosome. You need to bear in mind that by performing a PGD, it does not mean that screening of ALL genetic diseases are performed at the same time. This is because human beings have millions of gene and it is impossible to screen ALL of the genes in one go.

However, not all IVF patients need to undergo PGD. You may want to consider it, or your specialist may recommend it to you if:

• You or your partner (or both) are carriers of single gene mutations.
• You ended a previous pregnancy due to a serious genetic condition.
• You have a child with a serious genetic condition.
• Either of you has a family history of a serious genetic condition or chromosome problems.

The PGD procedure involves

1. You will undergo a normal IVF treatment and your eggs will be collected and fertilised.
2. An embryo is grown in the laboratory for a few days, until it has divided into around 8 cells.
3. An embryologist will remove one or two of the cells from the embryo.
4. The cells are tested to see if the embryo has a gene that causes a genetic condition.
5. If the embryo is free of any genetic condition, it is transferred to the womb.
6. Any remaining unaffected embryos can be frozen for later use.
7. Affected embryos will be allowed to perish.

Since PGD and PGS help detect genetic conditions and chromosomal abnormalities, they help IVF patients to decide if they wish to continue with pregnancy.

The Pros and Cons of PGD and PGS
Before you decide on undergoing PGD or PGS, your fertility consultant will explain their pros and cons to you, which include:

Pros

  • They can detect an inherited chromosomal or genetic issues and help prevent passing chromosomal or genetic diseases to the next generations
  • They are a form of early detection of chromosomal or genetic problems before the embryo is transferred back into the uterus.
  • They help increase a couple’s chances of conceiving a healthy child.
  • It allows older women to still have viable children.

Cons

  • There is a risk that embryos may be traumatized or destroyed due to damage during the biopsy process.
  • There is always a possibility of an undetected disease, as no form of testing can guarantee 100% accuracy
  • The test is expensive
  • You may not have any embryos to transfer after the IVF & PGD/PGS , which is frustrating for patients because after investing time, money & effort, the result can be disappointing
  • There is no guarantee that an embryo which had been screened will definitely get implanted after being transferred into the uterus. Therefore, there is no guarantee that a PGS/PGD embryo will give you a life birth.

If you and your partner are interested in or have any concerns about PGD and PGS, be sure to speak to your fertility specialist to address concerns, inquiries and options.