by Gary Finnegan: Health outcomes for children conceived using assisted reproduction technologies (ART) have improved significantly over the past two decades, according to a Danish-led study. However, the paper adds to existing evidence that transferring a single embryo per cycle is safer than implanting multiple embryos.
Rates of IVT have grown steadily since the practice was developed in the late 1970s. Early studies showed very significant gaps between the health of babies born through ART and those conceived naturally. But that gaps appears to be narrowing.
Fewer babies are being born preterm, healthier birthweights are more common, and the risk of stillbirth or of the child dying within the first years of life has fallen, according to the report, published in the journal Human Reproduction.
These findings come from the largest ever investigation into the health of ART babies over time. The research draws on data from more than 92,000 children in Denmark, Finland, Norway and Sweden.
Dr Anna-Karina Aaris Henningsen, from the Fertility Clinic at the Rigshospitalet, University of Copenhagen, Denmark, and her Nordic colleagues analysed the outcomes of 62,379 singletons (babies born alone) and 29,758 twins born between 1988 and 2007 in the four Nordic countries.
They compared them with control groups of 362,215 spontaneously conceived singletons and 122,763 spontaneously conceived twins born in the same countries in the same period.
“During the 20-year period of our study, we observed a remarkable decline in the risk of being born preterm or very preterm,” said Dr Henningsen. “The proportion of single ART babies born with a low or very low birth weight – less than 2500g or 1500g respectively – also decreased.”
The rates for stillbirths and death during the first year declined among both singletons and twins, and fewer ART twins were stillborn or died during the first year compared with spontaneously conceived twins, according to Henningsen.
“These data show that if there is a national policy to transfer only one embryo per cycle during assisted reproduction, this not only lowers the rates of multiple pregnancies, but also has an important effect on the health of the single baby,” she said.
Transferring several embryos in one cycle, even if it results in only a single baby, can still have a negative impact on the overall neonatal outcomes of singletons, the study found.
“By transferring only a single embryo, you not only avoid multiple births and all the health problems for the babies and mothers associated with these, but it also results in healthier ART singletons because there are fewer instances of ‘vanishing twins’ or procedures to reduce the number foetuses developing after successful implantation of several in the mother’s womb,” said Dr Henningsen.
Dr Henningsen said that other factors also contributed to the improvement in the health of ART babies over the past 20 years: better technical skills in the laboratory, improved clinical skills of the doctors, and a trend towards milder ovarian stimulation.
In addition, the culture media in which the embryos are first developed in the laboratory have improved in quality, as have the hormonal medications used to help women produce a sufficient number of high quality eggs at the right time.