When couples are counseled about fertility treatment, they are informed that babies conceived through fertility treatment are at increased risk of being born premature and at a low weight.
A new study, however, suggests the cause of this increased risk is more likely related to other factors – not the treatment itself.
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A group of researchers analyzing data on 248,000 births in Utah found the differences in birth weight and pregnancy length between couples who conceived naturally and those who used fertility treatment were small once certain individual characteristics of the parents and infants were taken into consideration.
The parents' underlying fertility problems and health conditions, as well as the infants' birth characteristics, such as their birth order, birth weight and whether they were a twin, play a more significant role than fertility treatment itself, researchers said.
About 5% of the infants in the study were conceived using medically-assisted reproduction. Sixty percent of these infants were conceived through fertility-enhancing drugs, 26% by assisted reproduction, including in vitro fertilization, and 14% by artificial insemination.
The researchers calculated that children who were conceived through fertility treatment were 10% more likely to be born premature and 9% more likely to have a low birth weight compared to the infants conceived naturally.
The outcomes of infants conceived with fertility drugs were similar to the infants conceived naturally, the researchers reported. The more invasive treatments, such as in vitro fertilization and artificial insemination, had a stronger association to adverse birth outcomes.
However, the researchers found that these differences weren't as significant once they adjusted for the mothers' health, parents' social and economic backgrounds, and infants' birth characteristics.
A subgroup of mothers in the study had experienced multiple pregnancies using both medically assisted reproduction and natural conception which allowed the researchers to compare different birth outcomes from the same mother.
"By comparing births from the same mother we were able to better isolate the impact on these births of medically assisted technologies," said Ken Smith, a professor of family studies and population science at the University of Utah.
Overall, researchers found the reproductive technology was not as an important determination of adverse birth outcomes as a mother's age, pre-pregnancy weight, genetic traits and infant's birth characteristics.
"This new evidence can go on to enrich existing health guidance about the risks and benefits of infertility treatments, hopefully raising awareness among families who are thinking about using medically assisted reproduction to help them conceive," added co-author Alice Goisis, an associate professor at the University College London Center for Longitudinal Studies, which assisted with the study.
The findings, published in journal Obstetrics & Gynecology, focused on births in Utah between 2009 and 2017.