Study: IVF Children Are Taller, Have Better Lipid Profiles


SAN DIEGO — New Zealand school-aged children who were conceived using in vitro fertilization were taller and had more favorable lipid profiles than those conceived naturally, a case-control study concluded.

Harriet Miles, M.D., and associates at the Liggins Institute of the University of Auckland studied 50 healthy children conceived via in vitro fertilization (IVF) with fresh embryos and 60 matched controls, when the children were 7–9 years old.

Participants were singletons, born at term, she said in an oral presentation at the annual meeting of the Endocrine Society.

After controlling for midparental height, members of the IVF group were considerably taller than the naturally conceived children. “This is surprising, as 15% of the IVF group were born small for gestational age, defined as weight below the 10th percentile,” said Dr. Miles, a pediatric endocrinologist.

According to standard growth prediction models, the IVF group would be up to half a standard deviation shorter than their naturally conceived peers, yet they were more than half a standard deviation taller.

“Another interesting finding is sexual dimorphism, with difference in height being more marked in females,” she said.

There were no differences in body composition between the two groups of children, yet IVF-conceived children had significantly higher insulin-like growth factor I (IGF-1), IGF-II, and insulin-like growth factor-binding protein 3 (IGFBP-3).

Their lipid profiles were more favorable, even when researchers controlled for age, sex, height, and percentage of body fat.

For example, the mean HDL cholesterol for IVF-conceived children was 1.61 mmol/L, compared with 1.51 mmol/L in naturally conceived controls.

There was a trend toward lower triglycerides and significantly lower LDL cholesterol in IVF-conceived children.

“Differences in growth and lipid metabolism in IVF children may be due to changes in genes influencing these factors, which are known to be imprinted,” Dr. Miles said.

She hypothesized that imprinting of these genes might be influenced by alterations in methylation patterns in the first few days after conception, as in the preimplantation period. A candidate gene to test this hypothesis has been found, and a future study will examine expression of this gene in IVF- and naturally conceived children.

In an interview, Dr. Miles explained that something as simple as the culture used during IVF may have an impact on methylation and expression of imprinted genes involved in growth and metabolism. The culture used in Australia and New Zealand contains glucose, for example.

Eric Surrey, M.D., president of the Society for Assisted Reproductive Technologies and a reproductive endocrinologist from Englewood, Colo., said in an interview after the conference that he found the study results “intriguing, but preliminary.”

Most studies of children conceived by IVF have focused on developmental issues and have found an occasional “blip,” but no significant, consistent differences between them and naturally conceived children. This may be the first study to address metabolic differences, he added.

“This is a small study, and I'm not sure any conclusions can be drawn from it. But anything suggesting differences in outcomes between children born using assisted reproductive techniques and those conceived naturally is very important to follow up on,” he said.

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