For kids conceived with assisted reproductive technology (ART), early life weight differences didn’t appear to linger long into adolescence, researchers reported.

Compared with those who were naturally conceived, children conceived via ART tended to be shorter and weigh less in early childhood, Ahmed Elhakeem, PhD, of the University of Bristol in England, and colleagues said.

However, as shown in their study in JAMA Network Open, these weight differences for kids conceived with ART were apparent only in infancy and then slowly dissipated throughout childhood. More specifically, adjusted mean weight differences were no longer significant by age 14:

• <3 months: -0.27 standard deviation units (95% CI -0.39 to -0.16)

• 17 to 23 months: -0.16 SD units (95% CI -0.22 to -0.09)

• 6 to 9 years: -0.07 SD units (95% CI -0.10 to -0.04)

• 14 to 17 years: -0.02 SD units (95% CI -0.15 to 0.12)

“Results appeared independent of multiple births and were at least partly mediated by birth weight and gestational age, particularly at younger ages,” the researchers pointed out.

They added that the findings should be “reassuring since differences in early growth were small, although there is a need for additional follow-up and studies with larger numbers into older ages to investigate the possibility of greater adiposity in adulthood.”

Not all children conceived via ART tended to be smaller babies, however. Elhakeem’s group found that this smaller size was seen only among those conceived by fresh — not frozen — embryo transfer versus natural conception. The difference in weight at ages 4 to 5 years was -0.14 (95% CI -0.20 to -0.07) SD units for fresh embryo transfer vs natural conception and 0.00 (95% CI -0.15 to 0.15) SD units for frozen embryo transfer versus natural conception.

This didn’t come as much of a surprise, as Elhakeem’s group said this finding aligned with prior research on the topic that’s linked smaller birth weight in offspring conceived via fresh embryo transfer versus natural conception, plus higher birth weight and large-for-gestational-age in offspring conceived via frozen-thawed embryo transfer compared with those conceived via fresh embryo transfer.

These early-life size differences also extended beyond just weight for children conceived via fresh embryo ART, the investigators reported. These children also tended to see smaller for waist circumference, total body fat percentage, and fat mass index. Though as with body weight, these differences tapered off by adolescence.

“There was little evidence that differences were driven by parental subfertility, given similar results when we compared offspring conceived via ART with those who were [naturally conceived] with parents who conceived after 12 months of trying and for whom conception occurred within a shorter period from the start of trying,” Elhakeem’s group noted.

A total of 26 study cohorts were included in the meta-analysis, which included data on 158,066 offspring — 4,329 of whom were conceived by ART. Cohorts stemmed from Europe, Asia-Pacific, and North America and mostly included kids born after 2002.

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