Since the birth of Louise Brown in 1978, the first baby ever born following conception by in-vitro fertilisation (IVF), thousands of infertile couples have gone down this route.
To increase the chance of them becoming parents, doctors can transfer up to 3 embryos, especially in the case of women older than 40.
This makes it more likely that the treatment will result in a live birth but also that they will end up getting twins. The probability of conceiving and giving birth to a multiples increases with the number of embryos transferred during IVF.
IVF techniques have been refined and improved overtime so the number of babies born as a result has increased in the last decades.
This has been observed with singleton births following IVF, which have more than quadrupled between 1992 and 2006, but the trend has also been seen with multiples births.
The UK Human Fertilisation and Embryology Authority estimates that the number of women giving birth to multiple babies has more than trebled over the same period – from 664 women to 2,312 women. Data from 2006 also indicates that 23% of women from all over the world who gave birth after IVF had twins or triplets.
Using more recent data, which aims at reducing the risks of multiple pregnancies from fertility treatment, says that about one in six IVF pregnancies now result in a multiple birth. In contrast, natural conceptions of twins occur only in about 1 in 80 births. This means that today, after IVF, women are 11 times more likely to have a multiple pregnancy than if they had conceived naturally.