How Many Embryos to Replace / Risks of Multiple Pregnancy


Replacing a single embryo, especially if it has been cultured to the blastocyst stage, is the best way of preventing multiple pregnancies, but the decision as to how many embryos to replace is a complex one and needs to be discussed with your Fertility Specialist, after taking into account your individualcircumstances, both medical and social.

 Occasionally, parents are faced with the decision of having to selectively terminate one more foetuses of a multiple pregnancy. This situation should be prevented if possible. However,

the final decision should always be yours!

Risks to the child

Prematurity is the major but not the only risk that is significantly increased in a multiple pregnancy ( twins triplets etc.)

Premature birth

The greatest risk associated with multiple pregnancies is premature birth:

  • The average gestation for twins is 37 weeks, compared to 40 weeks for singletons.
  • 10% of twin births take place before 32 weeks of gestation compared to just 1.6% of singleton births. The risk of delivery before 28 weeks of gestation is 6 times higher for twins than for singletons.
  • Preterm birth occurs in approximately 50% of twin pregnancies and is much higher than in singletons.
  • Studies have shown that almost 50% of twins have low or very low birth weight compared to 8% of singletons.
  • Evidence suggests that an average IVF twins are born three weeks earlier, and weigh between 800g and 1000g less than IVF singletons.

Perinatal mortality

  1. Twins are six times more likely to die in the first year of life than singletons (24.1:1000 compared with 4.4:1000).      

Neonatal care

  1. Between 40 to 60% of IVF twins are transferred to neonatal care units when they are born, compared with 20% of IVF singletons. In addition, research has shown that 12% of IVF twins require neonatal intensive care for more than four weeks compared to only 1.6% of IVF singletons.
  2. Of babies born before 26 weeks, 75% die very soon after birth and before admission to neonatal care. Those who are admitted have a 39% chance of survival, and 62% of those that survive have significant brain damage, retinopathy (visual problems) of prematurity, and/or ongoing oxygen dependence at their predicted due date.

Additional health complications

Additional complications increased with multiple births include:

  • Respiratory distress: 8% of twins require assisted ventilation and 6% suffer from respiratory distress syndrome compared to 1.5% and 0.8% for singletons    respectively.
  • Cerebral palsy: Twins are between four and six times more likely to suffer from  cerebral palsy than singletons. 12.6:1000 twins have cerebral palsy, compared  with 2.3:1000 singletons. A European multi-centre study reported that the risk of  cerebral palsy is increased by low gestational age and birth weight.
  • Delay in language development: 6.4% of IVF twins need speech therapy compared with 3.2% of IVF singletons.
  • Disability: Because twins are far more likely to be born preterm and of low birth weight, they are at much greater risk of disability. One study found that in 7.4% of twin pregnancies, at least one child has a disability.
  • Congenital malformations: One study found congenital malformations in 6.3% of twins compared with 4.7% of singletons.

Risks to the mother

The increased risks to the mother are variable with most being manageable, but some are serious and rarely life threatening. Management may require hospitalisation for prolonged periods and the need to have labour induced prematurely or a caesarean section for delivery.

Pregnancy complications

Complications can occur in a singleton pregnancy, but are much more common in multiple pregnancies and include:

  • Higher chance of a miscarriage.
  • Higher chance of pregnancy induced hypertension: 20% in women pregnant with twins compared with 1–5% in women pregnant with a singleton.
  • Higher risk of pre-eclampsia: up to 30% for twin pregnancies compared to 2–10% in singleton pregnancies.
  • Higher risk of gestational diabetes: up to 12% in twin pregnancies compared to around 4% for singleton pregnancies.
  • Higher chance of intervention in delivery: elective and emergency caesarean section rates are higher for mothers of twins.

Maternal mortality

Maternal mortality associated with multiple births is 2.5 times greater than with singletons. Maternal mortality in Australia is 7.1/100,000 of women giving birth, so increase to 14-17/100,000.

Psychosocial impact

Most parents would agree that the joy of having children is tempered with the stresses and strains of parenthood. These problems are often increased when patients face infertility and treatment programmes which, in some cases may be quite lengthy. Evidence suggests that multiple pregnancies further increase the stress of parenting and have an adverse effect on psychosocial wellbeing.

Mothers and families with twins or higher multiples are more likely to:

  • Experience severe stress
  • Increased risk of maternal depression
  • Have a reduced ability to work outside the home
  • Possibly an increased rate of divorce
  • Almost 20% of mothers of twins experience depression and marital difficulties, with first-time parents of twins and those who have had fertility treatment at even greater risk.
  • Twins demonstrate significantly lower levels of cognitive development than their singleton counterparts.
  • Parents of twins experience greater difficulties in parenting and more problems with child behaviour.
  • Mothers of low birth weight infants who require prolonged neonatal care experience greater levels of anxiety, and feel lower levels of attachment to their babies, than mothers of full-term, healthy infants.