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Outcomes improve in babies conceived by assisted reproduction, Nordic study shows

BMJ 2015; 350 doi: (Published 21 January 2015) Cite this as: BMJ 2015;350:h371
  1. Susan Mayor
  1. 1London

Perinatal outcomes have improved in children conceived by assisted reproductive technology (ART) over the past 20 years, figures from Nordic countries have shown. The data also showed fewer stillbirths or deaths in the first year of life and a reduction in the number of babies born preterm or with low birth weight.

Researchers analysed data on more than 92 000 children born from ART in Denmark, Finland, Norway, and Sweden from 1988 to 2007.1 Outcomes in the 62 379 ART singletons in the study were compared with a control group of more than 300 000 spontaneously conceived babies, and outcomes in the 29 758 twins born from ART were compared with all 122 763 spontaneously conceived twins born in the four countries during the study 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 the lead author, Anna-Karina Aaris Henningsen, of the Rigshospitalet’s fertility clinic at the University of Copenhagen in Denmark. The odds ratio of an ART singleton being born preterm (before 37 weeks) compared with a spontaneously conceived baby fell from 2.47 (95% confidence interval 2.09 to 2.92) in 1988-92 to 1.50 (1.43 to 1.58) in 2003-07.

“The proportion of single ART babies born with a low or very low birth weight—less than 2500 g or 1500 g, respectively—also decreased,” Henningsen reported. The odds ratio of birth weight below 2500 g fell from 2.94 (2.44 to 3.54) in 1988-92 to 1.49 (1.40 to 1.58) in 2003-07.

The rates of stillbirth and of death during the first year declined among singletons and twins, and fewer ART twins were stillborn or died during the first year than spontaneously conceived twins. The rate of stillbirths in singletons fell from 0.6% in 1988-92 to 0.3% in 2003-07, but it remained stable at around 0.3% in spontaneously conceived singletons over that period.

The researchers considered that the main reason for the improved outcomes in ART babies was the transfer of only one embryo in each cycle. The rate of twin deliveries from ART remained stable at about 23% from 1989 to 2002 but then decreased to 11.6% by 2007.

Henningsen said, “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 explained that transferring several embryos in one cycle, even if it results in only a single baby, can still negatively affect the overall neonatal outcomes of singletons. “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 of fetuses developing after successful implantation of several in the mother’s womb,” she explained.


Cite this as: BMJ 2015;350:h371


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