Cardiovascular autonomic nervous function in children conceived by assisted reproductive technology with frozen or fresh embryo transfer.

As a result of epigenetic changes, children conceived by assisted reproduction may be at risk of premature cardiovascular aging with notably increased blood pressures. Their cardiovascular autonomic nervous function is unknown. Therefore, this study investigated the cardiovascular autonomic nervous function in 8-12-yr-old children (51% girls) conceived naturally (n = 33) or by assisted reproduction with frozen (n = 34) or fresh (n = 38) embryo transfer by evaluating heart rate variability, during rest; from provocation maneuvers; and from baroreflex function. Heart rate and blood pressure response to provocation maneuvers and baroreflex function were comparable between children conceived naturally or by assisted reproduction. The mean RR-interval and high-frequency component of heart rate variability were lower in children conceived by assisted reproduction than in children conceived naturally. Children conceived by fresh embryo transfer had ∼17% lower heart rate-corrected standard deviation of normal-to-normal R-R intervals; ∼22% lower heart rate-corrected square root of the mean of the squared difference between successive R-R intervals; and ∼37% higher low-frequency/high-frequency ratio than naturally conceived children. Children conceived by assisted reproduction still had lower heart rate variability and vagal modulation than naturally conceived children after adjustment for confounders. Thus, these results raise the possibility of sympathetic predominance in children conceived by assisted reproduction. Therefore, it is important to reproduce these results in larger and older cohorts as sympathetic predominance relates with cardiovascular and metabolic diseases.NEW & NOTEWORTHY We observed that children conceived by assisted reproductive technology (both frozen and fresh embryo transfer) had lowered heart rate variability during rest as compared with children conceived naturally. During physiological stress maneuvers, however, the cardiovascular autonomic nervous regulation was comparable between children conceived by assisted reproductive technologies and naturally. Our findings highlight the potential that lowered heart rate variability during rest in children conceived by assisted reproductive technologies may precede premature hypertension.

Childhood BMI after ART with frozen embryo transfer.

STUDY QUESTION: Does BMI at 7-10 years of age differ in children conceived after frozen embryo transfer (FET) compared to children conceived after fresh embryo transfer (fresh-ET) or natural conception (NC)? SUMMARY ANSWER: BMI in childhood does not differ between children conceived after FET compared to children conceived after fresh-ET or NC. WHAT IS KNOWN ALREADY: High childhood BMI is strongly associated with obesity and cardiometabolic disease and mortality in adulthood. Children conceived after FET have a higher risk of being born large for gestational age (LGA) than children conceived after NC. It is well-documented that being born LGA is associated with an increased risk of obesity in childhood, and it has been hypothesized that ART induces epigenetic variations around fertilization, implantation, and early embryonic stages, which influence fetal size at birth as well as BMI and health later in life. STUDY DESIGN, SIZE, DURATION: The study 'Health in Childhood following Assisted Reproductive Technology' (HiCART) is a large retrospective cohort study with 606 singletons aged 7-10 years divided into three groups according to mode of conception: FET (n = 200), fresh-ET (n = 203), and NC (n = 203). All children were born in Eastern Denmark from 2009 to 2013 and the study was conducted from January 2019 to September 2021. PARTICIPANTS/MATERIALS, SETTING, METHODS: We anticipated that the participation rate would differ between the three study groups owing to variation in the motivation to engage. To reach the goal of 200 children in each group, we invited 478 in the FET-group, 661 in the fresh-ET-group, and 1175 in the NC-group. The children underwent clinical examinations including anthropometric measurements, whole-body dual-energy x-ray absorptiometry-scan, and pubertal staging. Standard deviation scores (SDS) were calculated for all anthropometric measurements using Danish reference values. Parents completed a questionnaire regarding the pregnancy and the current health of the child and themselves. Maternal, obstetric, and neonatal data were obtained from the Danish IVF Registry and Danish Medical Birth Registry. MAIN RESULTS AND THE ROLE OF CHANCE: As expected, children conceived after FET had a significantly higher birthweight (SDS) compared to both children born after fresh-ET (mean difference 0.42, 95% CI (0.21; 0.62)) and NC (mean difference 0.35, 95% CI (0.14; 0.57)). At follow-up (7-10 years), no differences were found in BMI (SDS) comparing FET to fresh-ET, FET to NC, and fresh-ET to NC. Similar results were also found regarding the secondary outcomes weight (SDS), height (SDS), sitting height, waist circumference, hip circumference, fat, and fat percentage. In the multivariate linear regression analyses, the effect of mode of conception remained non-significant after adjusting for multiple confounders. When stratified on sex, weight (SDS), and height (SDS) were significantly higher for girls born after FET compared to girls born after NC. Further, FET-girls also had significantly higher waist, hip, and fat measurements compared to girls born after fresh-ET. However, for the boys the differences remained insignificant after confounder adjustment. LIMITATIONS, REASONS FOR CAUTION: The sample size was decided in order to detect a difference of 0.3 SDS in childhood BMI (which corresponds to an adult cardiovascular mortality hazard ratio of 1.034). Thus, smaller differences in BMI SDS may be overlooked. As the overall participation rate was 26% (FET: 41%, fresh-ET: 31%, NC: 18%), selection bias cannot be excluded. Regarding the three study groups, many possible confounders have been included but there might be a small risk of selection bias as information regarding cause of infertility is not available in this study. WIDER IMPLICATIONS OF THE FINDINGS: The increased birthweight in children conceived after FET did not translate into differences in BMI, however, for the girls born after FET, we observed increased height (SDS) and weight (SDS) compared to the girls born after NC, while for the boys the results remained insignificant after confounder adjustment. Since body composition in childhood is a strong biomarker of cardiometabolic disease later in life, longitudinal studies of girls and boys born after FET are needed. STUDY FUNDING/COMPETING INTEREST(S): The study was funded by the Novo Nordisk Foundation (grant number: NNF18OC0034092, NFF19OC0054340) and Rigshospitalets Research Foundation. There were no competing interests. TRIAL REGISTRATION NUMBER: ClinicalTrials.gov identifier: NCT03719703.

Aortic distensibility is equal in prepubertal girls and boys and increases with puberty in girls.

Windkessel function is governed by conductance artery compliance that is associated with cardiovascular disease in adults independently of other risk factors. Sex-related differences in conductance artery compliance partly explain the sex-related differences in risk of cardiovascular disease. Studies on sex-related differences in conductance artery function in prepubertal children are few and inconclusive. This study determined the conductance artery compliance and cardiac function by magnetic resonance imaging in 150 healthy children (75 girls) aged 7-10 yr. Any sex-related difference in conductance artery function was determined with correction for other potential predictors in multivariable linear regression models. Our data showed that ascending [crude mean difference 1.11 95% confidence interval (CI) (0.22; 2.01)] and descending [crude mean difference 1.10 95% CI (0.09; 1.91)] aortic distensibility were higher in girls, but differences disappeared after adjustment for pubertal status and other identified potential predictors. Systolic and diastolic blood pressure, cardiac output, left ventricle (LV) systolic function, and total peripheral resistance did not differ between the sexes. In girls, heart rate was 7 beats/min higher, whereas pulse pressure (by 2 mmHg), LV end-diastolic volume index (by 7 mL), and stroke volume (by 5 mL) were lower. LV peak filling rate indexed to LV end-diastolic volume was 0.5 s-1 higher in girls. In conclusion, prepubertal girls and boys have equal conductance artery function. Thus, the well-known sex difference in adult conductance artery function seems to develop after the onset of puberty with girls initially increasing aortic distensibility.NEW & NOTEWORTHY Although it has been suggested that sex differences in conductance artery function may exist early in childhood, this study demonstrates that the well-known, sex-related difference in conductance artery stiffness (hence Windkessel function) in adulthood is not established before puberty. Thus, healthy prepubertal girls and boys have comparable conductance artery compliance. In contrast to previous studies, our study suggests that pubertal girls develop a more distensible aorta than prepubertal children.

Blood pressure and lipid profiles in children born after ART with frozen embryo transfer.

STUDY QUESTION: Are blood pressure (BP) and lipid profiles different between children conceived after ART with frozen embryo transfer (FET), fresh embryo transfer (fresh-ET), and natural conception (NC)? SUMMARY ANSWER: Girls conceived after FET had significantly higher systolic BP and heart rate compared with girls born after fresh-ET; boys conceived after FET had a slightly more favourable lipid profile compared with boys born after fresh-ET and NC. WHAT IS KNOWN ALREADY: Children conceived after ART with FET are more often born large for gestational age (LGA). LGA in general increases the risk of obesity, diabetes, and cardiovascular disease later in life. Studies on mice and humans on the whole ART population have raised concerns about premature vascular ageing and higher BP. The cardiovascular health of children born after FET is scarcely explored and the results are diverging. STUDY DESIGN SIZE DURATION: This study was part of the cohort study 'Health in Childhood following Assisted Reproductive Technology' (HiCART), which included 606 singletons (292 boys) born between December 2009 and December 2013: 200 children were conceived after FET; 203 children were conceived after fresh-ET; and 203 children were conceived naturally and matched for birth year and sex. The study period lasted from January 2019 to September 2021. PARTICIPANTS/MATERIALS SETTING METHODS: The included children were 7-10 years of age at examination and underwent a clinical examination with anthropometric measurements, pubertal staging, and BP measurement. Additionally, a fasting blood sample was collected and analysed for cholesterol, low-density lipoproteins (LDL), high-density lipoproteins (HDL), and triglycerides. Systolic and diastolic BP were converted to standard deviation scores (SDS) using an appropriate reference and accounting for height (SDS) of the child. The three study groups were compared pairwise using a univariate linear regression model. Mean differences were adjusted for confounders using multiple linear regression analyses. MAIN RESULTS AND THE ROLE OF CHANCE: Girls and boys conceived after FET had significantly higher birthweight (SDS) compared with naturally conceived peers (mean difference: girls: 0.35, 95% CI (0.06-0.64), boys: 0.35, 95% CI (0.03-0.68)). Girls conceived after FET had significantly higher systolic BP (SDS) and heart rate compared with girls conceived after fresh-ET (adjusted mean difference: systolic BP (SDS): 0.25 SDS, 95% CI (0.03-0.47), heart rate: 4.53, 95% CI (0.94-8.13)). Regarding lipid profile, no significant differences were found between the three groups of girls. For the boys, no significant differences were found for BP and heart rate. Lipid profiles were more favourable in boys born after FET compared with both boys conceived after fresh-ET and NC. All outcomes were adjusted for parity, maternal BMI at early pregnancy, smoking during pregnancy, educational level, birthweight, breastfeeding, child age at examination, and onset of puberty. LIMITATIONS REASONS FOR CAUTION: The participation rate varied from 18 to 42% in the three groups, and therefore selection bias cannot be excluded. However, extensive non-participant analyses were performed that showed almost no differences in background characteristics between participants and non-participants in the three groups, making selection bias less likely. WIDER IMPLICATIONS OF THE FINDINGS: The higher birthweight in children conceived after FET was associated with increased systolic BP (SDS) and heart rate in girls conceived after FET compared with fresh-ET. This may be an early indicator of compromised long-term cardiovascular health in this group. The study was not powered to investigate these outcomes and further studies are therefore warranted to confirm the findings. STUDY FUNDING/COMPETING INTERESTS: The study was funded by the Novo Nordisk Foundation (grant number: NNF18OC0034092, NFF19OC0054340) and Rigshospitalets Forskningsfond. The authors have no conflicts of interest to declare. TRIAL REGISTRATION NUMBER: ClinicalTrials.gov identifier: NCT03719703.