Infertility treatments involving ovulation induction are associated with an increased incidence of twins and higher order multiple pregnancy (4; Figure 11.1). The natural incidence of twins is one in eighty pregnancies and for triplets it is one in six thousand. Ovulation induction alone increases the incidence of twins four-fold. A study of twenty-four thousand IVF pregnancies found a 25-fold increase in the incidence of twins and a 350-fold increase in triplets.

Figure 11.1

Multiple pregnancy is regarded as 'high-risk' in obstetrics as all the potential complications of pregnancy occur more frequently. These include maternal problems such as anaemia, urinary tract infection, high blood pressure and bleeding. Miscarriage, premature delivery, poor placental function reducing the growth rate of the babies, perinatal mortality (stillbirths and babies dying in their first week) are all more frequent in twins. These problems are disproportionately more likely to occur with higher order pregnancies (Figure 11.2).

Figure 11.2

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