STUDY QUESTION Are there growth differences between singleton children born after frozen embryo transfer (FET), fresh embryo transfer (ET), and natural conception (NC)? SUMMARY ANSWER Adolescent boys born after FET have a higher mean proportion and increased odds of overweight compared to those born after fresh ET. WHAT IS KNOWN ALREADY Children born after FET have higher mean birthweights and an increased risk of large-for-gestational-age compared to those born after fresh ET and even NC. This raises questions about possible growth differences later in childhood. Previous studies on child growth after FET report partly conflicting results and lack long-term data until adolescence. STUDY DESIGN, SIZE, DURATION This was a cohort study based on national population-based registers, the Finnish Medical Birth Register and the Register of Primary Health Care visits, including singletons born after FET (n = 1825), fresh ET (n = 2933), and NC (n = 31 136) in Finland between the years 1995 and 2006. PARTICIPANTS/MATERIALS, SETTING, METHODS The proportions of overweight (i.e. age- and sex-adjusted ISO-BMI for children ≥ 25) were compared between the groups. Odds ratios (ORs) and adjusted odds ratios (aORs) of overweight were calculated. Adjustments were made for birth year, preterm birth, maternal age, parity, and socioeconomic status. Mean heights, weights, and BMIs were compared between the groups each year between the ages of 7 and 18. MAIN RESULTS AND THE ROLE OF CHANCE FET boys had a higher mean proportion of overweight (28%) compared to fresh ET (22%, P < 0.001) and NC (26%, P = 0.014) boys. For all ages combined, the aOR of overweight was increased (1.14, 95% CI 1.02–1.27) for FET boys compared to fresh ET boys. For girls, the mean proportions of overweight were 18%, 19%, and 22% for those born after FET, fresh ET, and NC, respectively (P = 0.169 for FET vs fresh ET, P < 0.001 for FET vs NC). For all ages combined, FET girls had a decreased aOR of overweight (0.89, 95% CI 0.80–0.99) compared to NC girls. Growth measurements were available for 6.9% to 30.6% of FET boys and for 4.7% to 29.4% of FET girls at different ages. LIMITATIONS, REASONS FOR CAUTION Unfortunately, we were not able to adjust for parental anthropometric characteristics. The growth data were not available for the whole cohort, and the proportion of children with available measurements was limited at the start and end of the follow-up. During the study period, mainly cleavage stage embryos were transferred, and slow freezing was used for ART. WIDER IMPLICATIONS OF THE FINDINGS The risk of overweight among FET boys warrants further research. Future studies should aim to investigate the mechanisms that explain this sex-specific finding and combine growth data with long-term health data to explore the possible risks of overweight and cardiometabolic disease in adulthood. STUDY FUNDING/COMPETING INTEREST(S) Funding was obtained from the Päivikki and Sakari Sohlberg Foundation, the Alma and K.A. Snellman Foundation (personal grants to A.M.T.), and the Finnish Government Research Funding. The funding sources were not involved in the planning or execution of the study. The authors declare no conflicts of interest. TRIAL REGISTRATION NUMBER N/A.

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冷冻胚胎移植后出生直至成年早期的单胎生长情况：一项芬兰登记研究

研究问题 冷冻胚胎移植（FET）、新鲜胚胎移植（ET）和自然受孕（NC）后出生的单胎儿童之间是否存在生长差异？摘要答案 与新鲜 ET 后出生的男孩相比，FET 后出生的青春期男孩的平均比例更高，超重的几率也更高。已知信息 与新鲜 ET 甚至 NC 后出生的孩子相比，FET 后出生的孩子平均出生体重更高，且大于胎龄的风险也更高。这引发了关于童年后期可能存在的生长差异的问题。之前关于 FET 后儿童生长发育的研究报告了部分相互矛盾的结果，并且缺乏青春期之前的长期数据。研究设计、规模、持续时间 这是一项基于全国人口登记册、芬兰医学出生登记册和初级卫生保健就诊登记册的队列研究，包括 FET 后出生的单身人士 (n = 1825)、新鲜 ET (n = 2933) ) 和 NC (n = 31 136) 于 1995 年至 2006 年间在芬兰进行。 参与者/材料、环境、方法 比较了 25 岁以上儿童的超重比例（即年龄和性别调整后的 ISO-BMI ≥ 25）。组。计算超重的优势比（OR）和调整后的优势比（aOR）。对出生年份、早产、产妇年龄、胎次和社会经济地位进行了调整。每年对 7 至 18 岁各组之间的平均身高、体重和 BMI 进行比较。主要结果和机会的作用 与新鲜 ET（22%， P < 0.001) 和 NC (26%, P = 0.014) 男孩。对于所有年龄段的综合而言，与新 ET 男孩相比，FET 男孩的超重 aOR 有所增加（1.14，95% CI 1.02-1.27）。对于女孩来说，在 FET、新鲜 ET 和 NC 后出生的女孩的平均超重比例分别为 18%、19% 和 22%（FET 与新鲜 ET 的 P = 0.169，FET 与 NC 的 P < 0.001） 。对于所有年龄段的综合而言，与 NC 女孩相比，FET 女孩的超重 aOR 较低（0.89，95% CI 0.80-0.99）。在不同年龄段，6.9% 至 30.6% 的 FET 男孩和 4.7% 至 29.4% 的 FET 女孩可进行生长测量。局限性和注意原因不幸的是，我们无法根据父母的人体测量特征进行调整。没有整个队列的生长数据，并且在随访开始和结束时具有可用测量值的儿童比例有限。研究期间主要移植卵裂期胚胎，并采用慢速冷冻进行ART。研究结果的更广泛意义 FET 男孩超重的风险值得进一步研究。未来的研究应该旨在调查解释这一性别特异性发现的机制，并将生长数据与长期健康数据结合起来，以探讨成年期超重和心脏代谢疾病的可能风险。研究经费/竞争利益 经费来自 Päivikki 和 Sakari Sohlberg 基金会、Alma 和 KA Snellman 基金会（AMT 的个人赠款）以及芬兰政府研究经费。资金来源不参与研究的规划或执行。作者宣称没有利益冲突。试用注册号 不适用。