IMPORTANCE People conceived using assisted reproductive technology (ART) make up anincreasing proportion of the world’s population.OBJECTIVE To investigate the association of ART conception with offspring growth and adiposityfrom infancy to early adulthood in a large multicohort study.DESIGN, SETTING, AND PARTICIPANTS This cohort study used a prespecified coordinated analysisacross 26 European, Asia-Pacific, and North American population-based cohort studies that includedpeople born between 1984 and 2018, with mean ages at assessment of growth and adiposityoutcomes from 0.6 months to 27.4 years. Data were analyzed between November 2019 andFebruary 2022.EXPOSURES Conception by ART (mostly in vitro fertilization, intracytoplasmic sperm injection, andembryo transfer) vs natural conception (NC; without any medically assisted reproduction).MAIN OUTCOMES AND MEASURES The main outcomes were length / height, weight, and bodymass index (BMI; calculated as weight in kilograms divided by height in meters squared). Each cohortwas analyzed separately with adjustment for maternal BMI, age, smoking, education, parity, andethnicity and offspring sex and age. Results were combined in random effects meta-analysis for 13age groups.RESULTS Up to 158 066 offspring (4329 conceived by ART) were included in each age-group metaanalysis, with between 47.6% to 60.6% females in each cohort. Compared with offspring who wereNC, offspring conceived via ART were shorter, lighter, and thinner from infancy to early adolescence,with differences largest at the youngest ages and attenuating with older child age. For example,adjusted mean differences in offspring weight were −0.27 (95% CI, −0.39 to −0.16) SD units at ageyounger than 3 months, −0.16 (95% CI, −0.22 to −0.09) SD units at age 17 to 23 months, −0.07 (95%CI, −0.10 to −0.04) SD units at age 6 to 9 years, and −0.02 (95% CI, −0.15 to 0.12) SD units at age 14to 17 years. Smaller offspring size was limited to individuals conceived by fresh but not frozen embryotransfer compared with those who were NC (eg, difference in weight at age 4 to 5 years was −0.14[95% CI, −0.20 to −0.07] SD units for fresh embryo transfer vs NC and 0.00 [95% CI, −0.15 to 0.15SD units for frozen embryo transfer vs NC). More marked differences were seen for body fatmeasurements, and there was imprecise evidence that offspring conceived by ART developedgreater adiposity by early adulthood (eg, ART vs NC difference in fat mass index at age older than 17years: 0.23 [95% CI, −0.04 to 0.50] SD units).CONCLUSIONS AND RELEVANCE These findings suggest that people conceiving or conceived byART can be reassured that differences in early growth and adiposity are small and no longer evidentby late adolescenc
