How many embryos to transfer?
The HFEA have stipulated that in the UK, three embryos can be transferred in women who are 40years or older. In women less than 40, only two embryos can be transferred and clinics should be encouraging women to have an elective single embryo transfer.
The reason behind this regulation is that a multiple pregnancy is a high risk pregnancy and it is better and safer for both the woman and the baby if the woman conceives one baby at a time.
The literature has shown that in women over the age of 40 replacing two embryos instead of one will lead to an increase in the chance of achieving a pregnancy and that that pregnancy is most likely to be a singleton pregnancy. In women less than 40 and particularly less than 37, replacing two embryos in preference to one will not increase the chance of pregnancy but will increase the risk of a multiple pregnancy .
However, when deciding upon the number of embryos to transfer, the decision should take into account not only the age of the woman but also the quality of embryos and number of previous failed cycles. The decision on how may embryos to transfer can often not be made therefore, until the day of embryo transfer. Certainly there is evidence to suggest good pregnancy rates in older women where good quality elective single blastocysts are transferred.
Risks of twin and triplet pregnancies
During pregnancy, mothers of twins and triplets are at greater risk of various serious health problems, as well as the risk of losing their babies.
- 20% of mothers carrying twins suffer from induced hypertension (high blood pressure), compared to only 1–5% of mothers of singletons
- the risk of pre-eclampsia is up to 30% for twin pregnancies compared to 2–10% in singleton pregnancies. Triplet pregnancies carry an even higher risk
- the likelihood of developing gestational diabetes is up to 12% for women carrying twins compared to only 4% for mothers with singleton pregnancies. Although the risks to the mother are fairly mild, gestational diabetes can increase the risk of the death to the unborn child or newborn baby
During or after birth:
During birth, mothers of twins are more likely to require intervention, more likely to experience problems.
- C-section is very common among twin births because complications with the birth are more likely with twins – for example, one or both babies are in a breech position
- the risks of a range of other problems such as haemorrhage and anaemia are also higher in twin births
- multiple births also carry the risk that, after the baby is born, the new mother will be at greater risk of stress and depression
- women with a history of infertility are more likely to find being a parent stressful. It is more likely to affect their health, even for singleton first-time mothers compared to naturally conceiving first-time mothers or mothers with a history of infertility who already have children
Even the less serious problems may result in the mother spending longer periods in hospital than would normally be necessary. Women may have to spend the last weeks of their pregnancy in hospital, and the birth may have to be induced early.
Risks for twins and triplets
The health risks for twins and triplets are greatly increased compared with those for singletons, mostly because multiples tend to be born prematurely and underweight. Premature and underweight babies account for half of all neonatal deaths. The risk of early and late miscarriage is also higher for twins than for singleton pregnancies.
Singleton babies are usually carried for about 40 weeks and tend to have normal birth weights. But many twins and triplets are born prematurely, before the normal time for healthy singletons. Prematurity can cause many problems and may even result in the death of the baby.
The problems caused by prematurity can range from those that, although serious, affect only the early stages of the child’s life, to those that have a devastating and lifelong impact.
- at least half of twins are born before 37 weeks and with low birth weights, making them at high risk of serious health problems and death
- over 90% of triplets are born before 37 weeks and many are born so early that they have long-lasting, serious health problems or die soon after birth
Early stage problems
- between 40–60% of IVF twins need to be transferred to the intensive care unit when they are born. Only 20% of singleton IVF babies need the same level of care
- 8% require assisted ventilation and 6% suffer from respiratory distress syndrome (breathing difficulties) compared with 1.5% and 0.8% for singletons respectively
- the risk of death around the time of birth is 3-6 times higher for twins and 9 times higher for triplets
Problems that may affect twins and multiples after the early stages of life are:
- a small percentage of twins have severe health problems that will affect their entire lives. Cerebral palsy, for example, affects about 1 in 80 twins compared with singleton babies (1 in 434 singleton babies)
- prematurity and low birth weight carry the risks of lower IQ and are linked with Attention Deficit Hyperactivity Disorder and long-lasting behavioural difficulties
- problems with language development is more common with twins. Twice as many twins need speech therapy compared with singletons
- according to a Japanese study, in 7.4% of twin pregnancies, at least one child had a disability, such as cerebral palsy, impaired sight, or congenital heart disease