THE case for transferring only a single embryo back to the mother in IVF has grown even stronger, because it removes the health risks associated with “vanishing twins”.
Although transferring multiple embryos during fertility treatment is standard practice in most countries, some countries already restrict the number of embryos that can be transferred to two or one. This is because of the much greater risks to the health of the mother and children associated with multiple pregnancies, greater stress for parents, and lifelong effects on the health of the children as a result of their lower birthweight.
Now two studies suggest that single embryo transfer (SET) is inherently safer, even compared with singleton births following transfer of multiple embryos.
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Diane De Neubourg’s team at the Middelheim Hospital in Antwerp, Belgium, compared 251 babies born after SET with singletons born after natural conception. “We found very little difference between the SET babies and those conceived naturally,” she told a meeting of the European Society for Human Reproduction and Embryology in Copenhagen, Denmark, this week. Their birthweights and the risk of premature birth were almost identical, for instance.
Many previous studies have shown that singletons born after multiple transfer are more likely to be of low weight and to be born prematurely (91av, 30 October 2004, p 11). Part of the reason for the higher risk, according to Anja Pinborg at the Rigshospitalet of the University of Copenhagen, is that 1 in 10 IVF singletons actually start life as twins. And the later in pregnancy that one twin dies, the higher the risk of neurological problems, she told the conference.
Her findings are based on a study of nearly 10,000 IVF babies born in Denmark between 1995 and 2001. Ultrasound scans at eight weeks were used to detect twin pregnancies. Vanishing twins do occur after normal conception, but the rate is far lower, at around 1 in 20 pregnancies.
The results should persuade more countries to limit the number of embryos that can be transferred, or at the very least stipulate that clinics tell women of the risks, Pinborg says.
“The results should persuade more countries to limit the number of embryos that can be transferred”
The good news is that while IVF children face higher risks during pregnancy and birth, in the long term they seem to do just as well as other children.
A follow-up study by a team led by Lize Leunens at the Free University of Brussels (VUB) in Belgium found that at age 8, children born as a result of intracytoplasmic sperm injection (ICSI) scored slightly higher on intelligence tests than those conceived naturally and did just as well in tests of motor skills. Leunens says the difference in IQ is probably because ICSI mothers are more attentive and provide more stimulation for their children.
