Fertility Treatments Don't Raise Odds for Smaller, Preemie Babies

January 12, 2022
Cara Murez

Babies conceived through infertility treatment are more likely to be born early and small.

But there are reasons other than medically assisted reproduction to explain this difference, a new study concludes.

"Rather than the infertility treatment itself, our new findings highlight the importance of parents' underlying fertility problems and health conditions, and infants' birth characteristics, such as their birth order and whether they are a twin, on birth weight and pregnancy term," said study co-author Alina Pelikh. She's a research fellow at the University College London Center for Longitudinal Studies in the U.K., which worked in partnership with the University of Utah in Salt Lake City.

For the study, researchers analyzed data on 248,000 births in Utah.

They found that differences in birth weight and length of pregnancy between couples who conceived naturally and those who used in vitro fertilization (IVF), artificial insemination or fertility drugs were insignificant once family circumstances were taken into account.

The study focused on births in Utah between 2009 and 2017 and various indicators of mothers' health, including pre-pregnancy body mass index (an estimate of body fat based on height and weight), blood pressure, age, education level and whether they had multiple births.

In all, about 5% of infants in the study were conceived through medically assisted reproduction (MAR).

Use of fertility-enhancing drugs was most common (60%), followed by assisted reproduction, including IVF (26%), and artificial insemination (14%).

Children who were conceived through MAR were 10% more likely to be born premature and had 9% greater odds of low birth weight compared to naturally conceived infants.

More invasive treatments -- such as IVF and artificial insemination -- were more strongly linked to adverse birth outcomes. Infants conceived using fertility drugs had outcomes more similar to those conceived naturally.

But differences in outcomes narrowed once the mothers' health, parents' social and economic background, and infants' birth characteristics were factored in.

Drawing from a statewide database, researchers zeroed in on a subgroup who had given birth to children using both MAR and natural conception during different pregnancies.

"By comparing births from the same mother we were able to better isolate the impact on these births of medically assisted technologies," said co-author Ken Smith, a professor of family studies and population science at the University of Utah.

The upshot: Once a mother's age, pre-pregnancy BMI and infants' birth characteristics were factored in, the siblings had similar pregnancy terms and birth weights.

That suggests that family circumstances and unobserved parental characteristics, such as genetic traits, are important when explaining the association between MAR and adverse birth outcomes.

"Obtaining similar results in highly diverse contexts -- in terms of demographics, fertility rates and access to the medically assisted reproduction treatments -- strengthens the argument that adverse birth outcomes among medically assisted reproduction conceived infants are unlikely to be driven by the reproductive technology itself," said co-author Alice Goisis, an associate professor at the UCL Center for Longitudinal Studies.

"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," she added.

The findings were published Jan. 6 in the journal Obstetrics & Gynecology.

More information

The National Library of Medicine has more on infertility.

SOURCE: University of Utah Health, news release, Jan. 6, 2022

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