Growing Up in New Zealand is this country’s largest contemporary longitudinal study of child development. The study has been designed to provide insight into the lives of children and young people growing up in the context of twenty-first century New Zealand. The Growing Up in New Zealand cohort recruited 6853 children representative of the current ethnic and socioeconomic diversity of births in Aotearoa, New Zealand in 2009 and 2010. The developmental wellbeing of the children has been tracked in detail over their first thousand days of life and every two to three years since. While the majority of the cohort are growing up healthy and happy, a significant proportion of children are growing up in families who have been persistently burdened with multiple stressors associated with economic, material and social hardship. This has created a disproportionate burden of poorer overall wellbeing outcomes and limited life course opportunities for these children from an early age. This paper will explore some of the evidence collected from the diverse cohort of New Zealand children and their families and whānau from before birth to middle childhood, highlighting the key findings and the utility of the evidence to improve wellbeing.

ABSTRACTImportancePeople conceived using assisted reproductive technology (ART) make up an increasing proportion of the world’s population, and their numbers are expected to continue rising.ObjectiveInvestigate association of ART conception with growth and adiposity outcomes from infancy to early adulthood in offspring from a large multinational multi-cohort study.Design26 population-based cohort studies.SettingEurope, Asia-Pacific, and North AmericaParticipantsInfants, children, adolescents, and young adults born from 1984 to 2018, with mean ages at assessment of growth/adiposity outcomes ranging from 0.6 month to 27.4 years.ExposuresConception by ART (conventional in vitro fertilisation and intracytoplasmic sperm injection) versus natural conception (NC).Main Outcomes and MeasuresLength/height, weight, and body mass index (BMI). Each cohort was analysed separately with adjustment for maternal BMI, age, smoking, education, parity, ethnicity, and offspring sex and age. Cohort results were combined in random effects meta-analysis for thirteen age groups.ResultsUp to 158,066 offspring (4,329 conceived by ART) were included in each age-group meta-analysis; 47.6% to 60.6% were female. Compared with NC, ART-conceived offspring were slightly shorter, lighter, and thinner from infancy to early adolescence. The differences in growth/adiposity outcomes were largest at the youngest ages and attenuated with older child age, e.g., adjusted standardised mean differences (95% confidence intervals) in offspring weight at age ‘<3 months’, ‘17 to 23 months’, ‘6 to 9 years’, and ‘14 to 17 years’ were -0.27 standard deviation (SD) units (−0.39 to -0.16), -0.16SD (−0.22 to -0.09), -0.07SD (−0.10 to -0.04), and -0.02SD (−0.15 to 0.12), respectively. There was no evidence that results were driven by parental subfertility or of difference between conventional in vitro fertilisation and intracytoplasmic sperm injection however, smaller offspring size appeared to be limited to offspring conceived by fresh but not frozen embryo transfer, compared with NC. More marked but less precise differences were observed for body fat measurements. There was imprecise evidence that offspring conceived by ART may develop greater adiposity by early adulthood.Conclusions and RelevancePeople conceiving or conceived by ART can be reassured that differences in early growth and adiposity are small and no longer evident by late adolescence.KEY POINTSQuestionIs conception by assisted reproductive technology associated with growth and adiposity from infancy to early adulthood?FindingsIn this multi-cohort study of up to 158,066 European, Asian-Pacific, and Canadian infants, children, adolescents, and young adults, those conceived using assisted reproductive technology were on average shorter, lighter, and thinner from infancy up to early adolescence when compared with their naturally conceived peers though differences were small across all ages and reduced with older age.MeaningParents conceiving or hoping to conceive through assisted reproductive technology and their offspring should be reassured that differences in early life growth and adiposity are small and no longer apparent by late adolescence.

Background: People conceived using assisted reproductive technology (ART) make up an increasing proportion of the world’s population. Our aim was to compare long-term growth and adiposity patterns between ART-conceived and naturally conceived (NC) offspring.Methods: We did two-stage sub-group meta-analyses of individual participant data from 26 European, Asia-Pacific, and Canadian cohorts with information on mode of conception and ≥1 postnatal growth/adiposity measurement in the offspring. Multivariable regression models (adjusted for maternal age, ethnicity, parity, body mass index (BMI), education, smoking, and offspring sex and age) were used to calculate differences in mean height, weight, BMI, waist circumference, body fat % and fat mass index (FMI). Cohort-specific results were combined using random-effects meta-analysis by age group.Findings Participants numbers in each meta-analysis varied from 152,833 (4,259 ART) to 3,111 (151 ART) offspring. Compared with NC, ART-conceived offspring were slightly shorter, lighter, and thinner from infancy to early adolescence, e.g., mean differences (95% confidence intervals) in height, weight, and BMI at age 6 to 9 years (ART minus NC) were -0.07 standard deviation (SD) units (-0.11 to -0.03), -0.07SD (-0.10 to -0.04), and -0.06SD (-0.12 to -0.01), respectively. Differences were largest at youngest ages and mostly attenuated with older age. Compared with NC, differences were clearer for fresh but not frozen-thawed embryo transfer. More pronounced but less precise differences were observed for waist circumference, body fat %, and FMI. There was some evidence that offspring conceived by ART may have greater adiposity in adulthood, e.g., difference in FMI at age >17 years was 0.23SD (-0.04 to 0.50). Interpretation Parents (and offspring) conceiving by ART can be reassured that differences in early growth and adiposity are small and no longer evident by late adolescence. However, studies with longer follow-up are needed to evaluate risk of increased adiposity in adulthood and potential associated co-morbidities.Funding Information: European Research Council, Horizon 2020, Medical Research Council, National Institute for Health Research, and the British Heart Foundation. Declaration of Interests: DAL has received support from Medtronic and Roche Diagnostics for research unrelated to that presented here. SMN has received support from Access Fertility, Ferring Pharmaceuticals, TFP, Modern Fertility, Ferring Pharmaceuticals, Roche Dignostics, and Merck for research unrelated to that presented here. All other authors declare no competing interests.Ethics Approval Statement: All the included cohorts had ethical approval from their relevant local or national ethics committees and all study participants gave informed consent or assent to participate in the Public respective cohorts and secondary data analyses.