Do more embryos mean a better pregnancy in IVF? Not necessarily

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Procreating and conceiving a child is a natural human tendency. Many of us are blessed with children. However, some couples do face obstacles in their journey towards parenthood.

Modern fertility treatments such as in-vitro fertilisation (IVF) have helped many couples to conceive.

Current IVF technology has seen many advancements, achieving a higher pregnancy rate. And IVF has also become safer for patients.

Common risks associated with an IVF procedure are ovarian hyperstimulation (OHSS) and multiple pregnancy.

The risk of OHSS has reduced dramatically with current IVF protocols.

However, the risk of multiple pregnancy varies depending on several factors, such as the age of the woman, quality of the embryo and number of embryos transferred into the womb.

A well-established IVF centre has its own medical guidelines pertaining to the number of embryos to be transferred into the womb.

Some countries have their own national guidelines, which advises fertility specialists on the number of embryos to be transferred based on patient and embryo factors.

Statistical probability points towards a higher pregnancy rate with increasing number of embryos transferred, i.e. the more embryos transferred into the womb, the higher the pregnancy rate.

So why are IVF doctors concerned about the number of embryos transferred?

As fertility doctors, we aim for the couple to have a healthy baby at the end of their journey, and not just rejoicing over a positive pregnancy test.

The journey towards parenthood does not stop with a positive pregnancy test, it's only the beginning of the journey.

If the pregnancy conceived are twins or triplets, it carries a significantly higher risk, which can lead to pregnancy loss and a great emotional scar for the couple.

Risks Of Multiple Pregnancies

Miscarriage: Twin and higher order multiple pregnancies pose a higher risk of miscarriage. First trimester complications such as bleeding and severe morning sickness are more common in a multiple pregnancy. These complications can lead to a higher miscarriage risk.

Prematurity: Prematurity is when the baby is born before 37 weeks of gestation. In a multiple pregnancy, the risk of the babies being born prematurely is significantly higher.

Complications to babies born prematurely depends on their birth weight and how early they were born.

Common complications are breathing difficulty (may need breathing support in an intensive care unit), infections of the gut, vision and hearing problems, and long-term mental retardation (cerebral palsy).

The risks of these complications are lower when the babies are born closer to term or when their weight is heavier.

Growth restriction (low birth weight): Low birth weight in a multiple pregnancy is commonly due to prematurity.

In a multiple pregnancy, babies are fighting for nutrition and the placenta may not be able to cope with the demand.

Nutrition may not be equally distributed between the babies, thus a growth discrepancy is common.

Babies of a multiple pregnancy are typically smaller than a singleton baby.

Medical conditions during pregnancy: Risks of developing medical complications such as high blood pressure, pre-eclampsia and gestational diabetes (GDM) in a multiple pregnancy are about two to three times higher.

The risk of GDM is higher due to the presence of more than one placenta, which can increase insulin resistance.

GDM, if not controlled early on, can lead to a big baby (macrosomia). This, in turn, leads to increased risk of birth trauma.

High blood pressure in a more severe form in pregnancy is known as pre-eclampsia.

Pre-eclampsia leads to growth restriction, and can also damage the mother's kidney and liver.

Caesarean section: The probability of a caesarean delivery increases in multiple pregnancy.

This does not mean that twin pregnancies are only delivered by a caesarean section. An obstetrician will determine the best mode of delivery in a twin pregnancy based on several factors.

However, in the presence of complications such as GDM, pre-eclampsia and growth restriction, the probability of delivering via a caesarean section is higher.

Looking For Solutions

As a fertility doctor, I always advise couples to aim for a singleton pregnancy, one at a time. The dilemma is always how to balance between the success rate of an IVF treatment and the risks associated with multiple pregnancy.

This is how it can be done:

Go for blastocyst embryo transfer (day five embryo transfer): In an IVF treatment, embryo/s can be replaced back into the womb at two stages, namely at cleavage stage (two- to three-day old embryo) or at blastocyst stage (five- to six-day old embryo).

An embryo at blastocyst stage gives a higher pregnancy rate. Only a good quality embryo can grow from cleavage stage to a blastocyst stage.

When embryo transfer is done with a blastocyst, ideally, one embryo is selected to be transferred into the womb.

This strategy gives a good pregnancy rate and minimises the risk of twin pregnancy.

However, there is a very small chance that the blastocyst can still spilt into twins.

Pre-implantation genetic diagnosis (PGS): Genetic testing can be done on the embryos to choose the embryo that is genetically normal.

This strategy helps the doctor, and also, the couple to choose the best embryo for embryo transfer, thus minimising the risk of a multiple pregnancy while maximising their chances of getting pregnant.

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