chances of multiples

Fertility treatments are performed in order to increase the chance of pregnancy, while aiming to avoid multiple pregnancy.

Multiple pregnancy carries a higher risk to mother and baby.  The risk is a little greater for twins than single babies but rises dramatically with three babies or more. The chance of premature birth and a low birth-weight, for example, is significantly higher in multiple pregnancies compared to a single or twin pregnancy. Accordingly the chance of complications and disability in the babies is greater too. This is why it is so important to keep the number of multiple pregnancy (more than twins) as low as possible.

It remains a dilemma to find the right balance between maximising the chance of pregnancy on the one hand, and minimizing the risk of a multiple pregnancy, on the other. Because couples undergoing fertility treatment do this in order to have a healthy child or children, taking risks that are too great during treatment to achieve pregnancy can unfortunately run counter to their ultimate goal.

The chance of a multiple pregnancy as a result of fertility treatment depends on, amongst other things, the type of treatment and your personal decisions.

Ovarian hyperstimulation

Treatments that involve the use of drugs that trigger multiple follicles to mature increase the chance of a multiple pregnancy. Because of this, women are closely monitored during treatment. If the ovaries react too strongly, too many follicles mature, then the treatment can be interrupted to prevent a woman becoming pregnant that month because of the risk of a multiple pregnancy. The maximum number of follicles that is regarded as being medically acceptable is not fixed but depends on factors such as the type of treatment and the reason for the fertility problem. This is normally discussed with the couple. During mild hyperstimulation, the acceptable number of follicles would normally be two, or three at the most. In this scenario, it is very difficult to control the number of fertilisations that may occur.

IVF and ICSI treatment

Under IVF treatments, the risk of a multiple pregnancy is, in principle, easier to control because it depends on the number of embryos that are replaced into the womb. Because of this, in Singapore a strict embryo replacement policy is adhered to. When three embryos are replaced, the risk of twins is approximately 25%. There is also a very small chance of triplets - one of the embryos can spontaneously split into one-egg twins. However the chance of both embryos doing this - leading to quadruplets - is minute.

In the event of a high multiple pregnancy, the opportunity to “reduce" the number of embryos is sometimes offered. This is called selective reduction, and will always be a very difficult decision for a couple to make. It is usually carried out as soon as technically possible to keep the risks low – usually between 9 and 12 weeks. The most common method used is to pass a needle directly into the embryo sacs in the womb in which the foetuses being reduced lie using ultrasound to guide the needle. A chemical solution is then injected into the foetus, which kills it immediately. The foetus is usually reabsorbed into the mother’s body although it may be lost like a miscarriage. Selective reduction can improve the chances of survival for the remaining foetuses but is not without risk. You need to ensure you get good obstetric advice and support in relation to your individual risks.