Feb. 18 (UPI) -- Children conceived using in vitro fertilization have a slightly higher risk of dying during infancy than those conceived naturally, a study published Tuesday in the journal Sterility and Fertility suggests.
In an analysis of more than 7,000 children who died before turning 1 year old, researchers at the Karolinska Institutet in Sweden noted that those conceived using IVF had a 45 percent higher risk of death during early life than others.
They linked this increased risk to the fact that a higher number of IVF children are born prematurely, and emphasized that the risk of infant mortality is still very small for both groups.
"It is important to note that even if we on a group level can see a somewhat increased risk of infant mortality after IVF, the absolute risk for each individual is still very small," co-author Kenny Rodriguez-Wallberg, associate professor of oncology and pathology at Karolinska Institutet, said in a press release. "It is also reassuring to know that there is no increased risk of mortality in this group of children beyond the first year of life."
Beyond 1 year of age, the risk of mortality was similar for all children, regardless of conception method, she added.
Prior studies have shown that IVF-induced pregnancies come with an increased risk of low birth weight, premature birth and birth defects. Although the reasons for this are still being studied, these risks have partly been linked to the increased probability of twin births after IVF treatment.
For this most recent study, the researchers selected only singleton children and compared mortality in children conceived through different types of assisted reproductive techniques with children who were conceived naturally. They analyzed data from more than 2.8 million children born in Sweden over a period of 30 years -- about 43,500 of which were the result of assisted reproduction.
In all, 7,236 children died before turning 1 and, of these, only 114 were conceived using assisted reproductive techniques. After adjusting for the mother's age and earlier infertility, the researchers found that the children conceived using IVF had a 45 percent higher risk of death before 1 year of age than children conceived naturally.
The level of risk varied depending on which type of assisted reproductive technique was used, and how many days had passed since birth. The risk gradually declined after the first weeks of life, the authors noted.
Overall, for example, during the first week of life, the children conceived following transfer of a frozen embryo had a more than two-fold higher risk of death than the children conceived naturally. This was, however, based on a small sample of children conceived this way and, after one week, the risk dropped to about the same level as the naturally conceived children.
In addition, infants conceived from transfer of a fresh embryo or using an intra-cytoplasmic sperm injection -- where a single sperm is injected into the egg -- did not have a higher risk of death than naturally conceived children, regardless of the number of days since birth.
The leading causes of infant mortality among children conceived with assisted reproductive techniques included respiratory distress, incomplete lung development, infections and neonatal hemorrhage, which are conditions often linked to premature birth.
"Our results indicate that the kind of assisted reproductive technique used may make a difference, and therefore it is important to further investigate what causes or underlying mechanisms are behind the risks," said co-author Anastasia Nyman Iliadou, an associate professor medical epidemiology and biostatistics at Karolinska Institutet. "They also show the need for extra attention and care of children conceived with IVF, especially during the first week of life."