Abstract
Objective:
To evaluate whether children conceived by assisted reproductive technologies (ART) or ovulation induction (OI) have greater cardio-metabolic risk than children not conceived by treatment.
Design:
Clinical assessments in 2018–2019 in the Upstate KIDS cohort
Setting:
Clinical sites in New York
Patients:
333 singletons and 226 twins from 448 families
Interventions:
Mothers reported their use of fertility treatment and its specific type at baseline, around 4 months postpartum. High validity of self-reported ART use was previously confirmed. Children were followed from infancy through 8–10 years of age. A subgroup was invited to participate in clinic visits.
Main outcome measures:
Blood pressure (BP), arterial stiffness by pulse wave velocity (PWV), anthropometry, and body fat by bioelectrical impedance were measured (n=559). Plasma lipids, C-reactive protein (CRP), and hemoglobin A1c (HbA1c) were measured among 263 children with blood samples.
Results:
Children averaged 9.4 years old at clinic visits. About 39% were conceived by fertility treatment (18% ART and 21% OI). Singletons conceived by fertility treatment (any type or by ART or OI specifically) did not statistically differ in systolic or diastolic BP, heart rate or PWV. Singletons conceived by OI were smaller than singletons not conceived by treatment, but the latter averaged higher BMI (0.41 (SD 1.24) z-score) than national norms. Twins conceived with either treatment had lower BP than twins not conceived by treatment. However, OI twins had significantly higher arterial stiffness (0.59; 95% CI: 0.03, 1.15 m/s) which was attenuated after accounting of maternal blood pressure (0.29; 95% CI: −0.03, 0.46 m/s). Twins did not significantly differ across groups in size or fat measures. Mode of conception was not associated with lipids, CRP or HbA1c.
Conclusions:
Clinical measures at age 9 years did not indicate greater cardio-metabolic risk in children conceived by ART or OI compared to no treatment.
Clinical Trial Registration:
Keywords: assisted reproductive technology, ovulation induction, cardiovascular, singletons, twins
Capsule
Measures of blood pressure, arterial stiffness, anthropometry, and related biomarkers at age 9 years did not indicate greater cardio-metabolic risk in children conceived by fertility treatment compared to no treatment.
Introduction
Increasing numbers of children are conceived by fertility treatment, including assisted reproductive technologies (ART). As reported to the Centers for Disease Control and Prevention (CDC) in 2017, almost 200,000 ART procedures took place across the United States (U.S.), contributing to 1.9% of all births (1). This proportion is nearly double that of the 1% reported in 2001 (2). The increase can be attributed to trends in delayed childbearing (3), increased success rates, and the acceptance of using these technologies. Nationally, while singleton deliveries have increased, the percent of multiple births conceived by ART remain substantial, contributing to over 17% of all multiples born (1). Nevertheless, ART twins remain understudied, particularly with respect to life-course health outcomes.
One area of particular concern is cardio-metabolic outcomes in children conceived by ART (4). Much evidence has substantiated the Developmental Origins of Health and Disease hypothesis (5); that in response to a suboptimal environment in critical windows of development, permanent adaptations are made to the body which increase risks of later chronic disease including cardio-metabolic outcomes. Epigenetic changes are suspected to be the mechanism behind these adaptations (6). Nutrient deficiency in the extreme as shown in famine studies particularly draw attention to the periconception period as a window of importance for establishment of these epigenetic marks (7). Hence, embryo culture is suspect, as optimal culture remains elusive. For instance, a basic science experiment tested the addition of melatonin to culture to prevent vascular dysfunction in mice after ART (8). Apart from embryo culture, hormonal stimulation also has downstream impact on endometrial receptivity and oocyte development.(9) Moreover, nutrient competition may play a role with singletons resulting from double versus single embryo transfers experiencing more adverse perinatal outcomes (10).
A meta-analysis conducted in 2017 reported findings from 19 studies with over 2000 children conceived by in vitro fertilization or intracytoplasmic sperm injection (IVF/ICSI) and 4000 non-ART offspring (11). Increases in systolic (SBP) and diastolic blood pressure (DBP) were observed among children conceived by ART in 10 studies but stratifying cohorts by year they were conceived eliminated the association among children conceived after the year 2000. Multiple reasons could account for the period effect, including technological advances in ART techniques and young age of the children for assessing cardio-metabolic outcomes (studies of children conceived by IVF after 2000 included children who were 4–6 years of age). Studies have not observed differences in body mass index (BMI), and a limited number of studies (n=5) on lipid metabolism showed no difference; too few studies are available on more intensive assessments such as arterial stiffness or thickness.
Since this meta-analysis, additional studies have evaluated cardio-metabolic risks with mixed findings (12–20). Differences in findings may be attributed to small sample size, use of various comparison groups, limited adjustment for family history, and variation in measurement intensity. Almost all investigations were conducted outside the U.S., which may not be as widely representative of all assisted conceptions, as many countries currently mandate use of single embryo transfer (SET), which the U.S. does not, along with other technique differences.
In response to the limitations of existing studies, the current investigation examined differences in cardio-metabolic outcomes among 8–10 year old children from New York State by mode of conception (i.e., by ART including both IVF and ICSI, and by OI). We comprehensively measured anthropometrics, bioelectric impedance (BIA) for body fat, blood pressure, pulse wave velocity (PWV), plasma lipids, hemoglobin A1c (HbA1c) and C-reactive protein. We added to previous investigations by including both singletons and twins using population-based sampling, accounting for parental cardio-metabolic factors and having a non-ART treatment group. We hypothesized that children conceived by ART would have elevated blood pressure and arterial stiffness but would otherwise not differ in growth or body fat.
Methods
Study Design and Population
The Upstate KIDS Study was designed to examine the health of children conceived by fertility treatment (21). All women whose singletons were conceived using fertility treatment, as indicated on vital records, and delivered between 2008–2010 were recruited to participate in the study by letter sent approximately 2–4 months after delivery. For each successful recruit, 3 mothers of singletons not conceived with fertility treatment and living in the same perinatal region of New York State were also recruited. Random sampling with frequency matching on perinatal regions of birth was conducted. Mothers of all live twins, triplets, and other multiples, regardless of means of conception, were recruited to participate as well. Treatment exposure groups were not matched other than by region of birth and plurality. The study enrolled 5,034 mothers (27% of those approached) with their 6,171 newborns.
The current analysis is part of a second phase of follow-up which began in 2015 with invitation to mothers of 5529 children to complete a survey. This follow-up excluded triplets and quadruplets due to small numbers (n=134) and children who had withdrawn (n=486) or were lost to follow-up (n=22). Of those remaining, 4644 (84%) children living within 2 hours of one of four study sites across the state (i.e., University at Albany, University at Buffalo, University of Rochester, New York University Langone Health) were invited to attend a clinic visit. From 2017 to 2019, 559 (12%) children completed a visit when they were 8–10 years old (Supplemental Figure 1).
The New York State Department of Health and the University of Albany Institutional Review Board (IRB) (NYSDOH IRB #07–097; UAlbany #08–179 and #15E-122) approved the study and served as the IRB designated by the National Institutes of Health under a reliance agreement. Mothers provided written informed consent. Children also assented to clinic visits.
Fertility treatment ascertainment
Mothers completed a baseline questionnaire between 2008–2010 at approximately 4 months postpartum and were asked to select all medical services or medications used to assist them with conceiving this pregnancy. ART was defined as use of in vitro fertilization (with or without ICSI), assisted hatching, frozen embryo transfer, gamete intrafallopian transfer, and zygote intrafallopian transfer, with or without the use of donor eggs or embryos. Ovulation induction (OI) was defined as use of oral or injectable medications (e.g., Clomid® or gonadotropins) with or without intrauterine insemination (IUI) (21). We found high sensitivity (93%) and specificity (99%) for maternal report of ART use compared to ART use identified by linkage with the Society for Assisted Reproductive Technology Clinic Outcome Reporting System (22).
Anthropometric measures
Study clinic visits occurred between 2017 to 2019. Clinic staff measured both mothers and children with no knowledge of their fertility treatment status. Anthropometry measures included weight, height, and waist and hip circumferences. Height was measured in duplicate using a portable stadiometer and weight using an electronic scale. Children wore light clothing without shoes. Waist circumference over the iliac crest was measured twice to the nearest millimeter using a tape measure. Hip circumference was measured in duplicate by sliding the tape measure up and down to locate the widest circumference. Tolerances for measures were given such that if the differences exceeded a threshold (i.e., 0.5 cm for height and circumferences, 0.454kg for weight), a third measure was taken and the two closest measures of the three were averaged. Body mass index (BMI) was calculated as weight over height-squared (kg/m2). Children’s age and sex specific z-scores for weight, height and BMI were derived using the CDC growth charts (23). A cutoff of BMI>85th percentile was used to categorize children as overweight/obese (24). Body fat was measured twice using BIA from the Quantum V portable device (RJL Systems Inc., Clinton Township, MI, USA) while the child was supine. Data included total as well as segmental body fat. BIA data were checked for outliers and multiple records in the same clinic visit were averaged.
Cardio-metabolic measures
SBP, DBP, mean arterial pressure (MAP), and heart rate were measured using the Welch Allyn Connex® ProBP™ 3400 digital blood pressure device (Skaneateles Falls, NY, USA) prior to the blood draw. Cuffs were appropriately sized after measurement of arm circumference. Children rested in the sitting position for 10 minutes before blood pressure measurement was taken from the upper right arm. The first blood pressure measurement was voided and two others were taken with 5 minute resting periods in between. If the difference between the two measurements exceeded 5mmHg, a third measure was taken. Measures were averaged. Pediatric clinical cut-points at the 95th percentile for sex, age and height were used to assess hypertension by SBP and DBP (25).
A measure of arterial stiffness was conducted by carotid-femoral pulse wave velocity (PWV) using the SphygmoCor XCEL System (AtCor Medical Inc., Itasca, IL, USA) which has previously been validated in pediatric research, especially as a tonometer at the femoral artery may be perceived as too invasive (26). The system measured carotid to femoral wave by the use of a tonometer at the carotid and cuff wrapped around the upper thigh. The femoral pulse is detected using volumetric displacement detected with the thigh cuff. Following 10 minutes of rest, two measurements were taken while supine. A third measure was taken if the tolerance of 0.5m/s was exceeded. The device includes an internal quality control system but waveforms were also stored electronically and examined as necessary for data cleaning of discrepant measures. If two PWV measures differed by more than 0.5m/s, and a third measurement was available, the median of the three values was taken; otherwise, if the third measurement was unavailable, the average of the two values was taken. Twenty-five (4%) children required a third measure (with 5 [1%] not compliant to another attempt) and 45 (8%) only had a single measurement. As even 1 measurement would be better than missing data, sole measurements were kept in analyses (27). Interindividual coefficients of variations averaged 0.1% to 5.3% on all exam measures taken using the difference in measures taken on the same day.
A subgroup of 263 children – 155 children conceived without treatment, 64 children by OI and 44 children by ART – agreed to a blood draw. Blood was processed for plasma and packed red blood cells. Due to the distance some families traveled to attend clinic visits and the scheduling to accommodate after school hours, fasting samples were not attempted. Non-fasting cutoffs have been set by national guidelines on pediatric lipid screening. Samples were frozen in −80°C until analysis at University of Minnesota where one sample was lost during transfer. Plasma lipids (mg/dl) and high sensitivity C-reactive protein (CRP, mg/L) were measured using the Roche COBAS 8000 chemistry analyzer (Roche Diagnostics, Indianapolis, IN, USA). Analytic variation ranged from 2–6%. The limit of detection for CRP was 0.15mg/L with 95 (36% of 263) children measuring below this limit. Four values of CRP >10mg/L were excluded (3 no treatment, 1 OI) as outlying values potentially indicating infection. Packed red blood cells were used to measure HbA1c using Non-porous Ion Exchange High Performance Liquid Chromatography (HPLC) (Tosoh Automated Analyzer HLC-723G8, Tosoh Bioscience, Inc., South San Francisco, CA, USA). The coefficient of variation was 1.16%.
Covariates
Maternal race/ethnicity, education, marital status, and parental weight and height (from which maternal pre-pregnancy and paternal BMI were derived) were reported by mothers on the baseline questionnaire at about 4 months postpartum. Maternal age and insurance status at delivery and children’s plurality, sex, birthweight, and gestational age came from vital records. Small and large for gestational age were derived using a U.S. reference of births (28). Maternal SBP, DBP, and PWV were measured using a similar protocol at the clinic visit. Mothers also answered questions regarding medical diagnoses and medications for diabetes and hypertension at time of visit. Maternal hypertension was defined by blood pressure ≥130/80 mmHg SBP/DBP(29) or self-report of diagnosis at time of visit. Elevated maternal arterial stiffness was defined as ≥10m/s(30) and elevated HbA1c ≥5.7%(31) or a diabetes diagnosis. Hemoglobin variants were noted but had no material impact on classifications (32).
Statistical analysis
Baseline characteristics by fertility treatment status and by specific type of treatment (ART or OI/IUI) were compared by Kruskal-Wallis tests or chi-square tests. For consistency, the non-parametric tests were applied to comparisons of continuous baseline characteristics because some of their distributions are skewed and cannot be assumed normally distributed. Similarly, characteristics by agreement to clinic visit and by blood draw were compared. Analyses of covariance (ANCOVAs) were used for continuous dependent variables to estimate mean differences (95% CIs), and logistic regression was used for dichotomized outcomes to estimate Odds Ratios (95% CIs). For models that included twins, generalized estimating equations were used to account for within-family variance. Models predicting anthropometric and cardiovascular outcomes were adjusted for child age and sex, maternal age at delivery, race/ethnicity, education, insurance, pre-pregnancy BMI, and clinic site. Due to statistical interactions with blood pressure (p-interaction<0.05), models for clinical measures were stratified by plurality. Singletons conceived with treatment were compared with singletons not conceived by treatment, and twin specific comparisons were separately conducted. In supplemental analyses, paternal BMI was added to anthropometric models and maternal cardiovascular measures at the time of clinic visit were added to blood pressure models, to further control for familial risk. Tests for mean differences in lipids, CRP, and HbA1c were adjusted for child’s age at clinic visit, sex, plurality, clinic site, and maternal age, race/ethnicity, and education. Additional models adjusted for maternal dyslipidemia and hyperglycemia. Due to few missing data points (<5), complete case analysis was used. All analyses were conducted using SAS (v9.4).
Results
Mothers, who gave birth to children conceived by fertility treatment, were on average 4 years older than mothers who did not use treatment (Table 1). Other differences observed included that women with fertility treatment had higher education and were more likely to hold private insurance. Children were 8–10 years old at the time of examination. In the non-treatment group 220 (81%) children were singletons, while in the fertility treatment group 113 (64%) were singletons. When compared against family characteristics of those who did not participate in clinic visits, those who attended clinic visits had a higher proportion who were college or more educated and held private insurance, substantiating the observations that higher SES is associated with retention and justifying keeping these variables in adjusted models (Supplemental Table 1). However, birthweight and other characteristics were similar. Furthermore, no differences in clinical measures of children who agreed to a blood draw (n=214) compared to those of children who did not agree (n=234) were identified (data not shown).
Table 1.
Baseline characteristics by fertility treatment status, Upstate KIDS Study (2008–2010))
| No fertility Treatment | Any fertility Treatment | OI/IUI | ART | P-value comparing No treatment vs. Any treatment | P-value comparing OI/IUI vs. A | |
|---|---|---|---|---|---|---|
| N (%) | 271 (60.49) | 177 (39.51) | 95 (21.21) | 82 (18.30) | ||
| Maternal age at delivery(years)a,b | 29.80 (5.56) | 33.75 (5.23) | 32.61 (5.20) | 35.06 (4.97) | <.0001 | 0.0049 |
| Non-Hispanic Whiteb | 231 (85.24) | 156 (88.14) | 90 (94.74) | 66 (80.49) | 0.3823 | 0.0035 |
| College/Advanced degreea | 153 (56.46) | 135 (76.27) | 71 (74.74) | 64 (78.05) | <.0001 | 0.6050 |
| Private insurancea | 207 (76.38) | 171 (96.61) | 92 (96.84) | 79 (96.34) | <.0001 | 0.3127 |
| Married/living as married | 234 (87.64) | 164 (93.18) | 86 (91.49) | 78 (95.12) | 0.0589 | 0.3402 |
| Maternal hypertension (>120/80) | 105 (38.75) | 66 (37.29) | 37 (38.95) | 29 (35.37) | 0.7563 | 0.6232 |
| Maternal prediabetes | 34 (12.55) | 26 (14.69) | 13 (13.68) | 13 (15.85) | 0.5150 | 0.6843 |
| Maternal pre-pregnancy BMI (kg/m2) | 25.99 (22.14, 31.61) | 24.56 (22.14, 29.53) | 24.89 (22.21, 32.27) | 24.03 (21.92, 27.95) | 0.1862 | 0.4948 |
| Paternal BMI (kg/m2) | 26.69 (24.36, 31.19) | 27.34 (24.62, 31.44) | 27.32 (24.41, 30.51) | 27.70 (25.01, 32.32) | 0.3288 | 0.9812 |
| Pluralitya | <.0001 | 0.4609 | ||||
| Singleton | 220 (81.18) | 113 (63.84) | 63 (66.32) | 50 (60.98) | ||
| Twin | 51 (18.82) | 64 (36.16) | 32 (33.68) | 32 (39.02) | ||
| Male | 142 (52.40) | 93 (52.54) | 52 (54.74) | 41 (50.00) | 0.9762 | 0.5291 |
| Birthweight (grams)a | 3361 (2853, 3755) | 3085 (2585, 3524) | 3050 (2555, 3557) | 3150 (2665, 3487) | 0.0008 | 0.9352 |
| Gestational Age (weeks)a | 39 (38, 40) | 38 (37, 39) | 38 (37, 39) | 38 (37, 39) | 0.0001 | 0.9735 |
| Age at Visit (Years) | 9.40 (0.58) | 9.51 (0.57) | 9.48 (0.55) | 9.55 (0.59) | 0.0709 | 0.8453 |
| Clinic Site b | 0.0670 | 0.0019 | ||||
| Albany | 104 (38.38) | 61 (34.46) | 27 (28.42) | 34 (41.46) | ||
| Buffalo | 45 (16.61) | 30 (16.95) | 21 (22.11) | 9 (10.98) | ||
| New York City | 6 (2.21) | 13 (7.34) | 2 (2.11) | 11 (13.41) | ||
| Rochester | 116 (42.80) | 73 (41.24) | 45 (47.37) | 28 (34.15) | ||
| Size for gestational age | 0.3235 | 0.2407 | ||||
| Small | 37 (13.65) | 33 (18.64) | 19 (20.00) | 14 (17.07) | ||
| Appropriate | 211 (77.86) | 132 (74.58) | 67 (70.53) | 65 (79.27) | ||
| Large | 23 (8.49) | 12 (6.78) | 9 (9.47) | 3 (3.66) | ||
| Gestational diabetesa | 26 (9.59) | 29 (16.38) | 15 (15.79) | 14 (17.07) | 0.0323 | 0.8180 |
| Preeclampsiab | 32 (11.81) | 25 (14.12) | 8 (8.42) | 17 (20.73) | 0.4720 | 0.0190 |
| Childhood cardio-metabolic risk | ||||||
| N (%) | 319 (57.07) | 240 (42.93) | 126 (22.54) | 114 (20.39) | ||
| SBP (mmHg)a | 106.09 (10.12) | 103.90 (9.36) | 103.39 (10.25) | 104.49 (8.24) | 0.0391 | 0.5231 |
| DBP (mmHg) | 63.04 (6.65) | 62.12 (6.33) | 62.04 (6.96) | 62.20 (5.56) | 0.1467 | 0.9188 |
| Heart rate (beats/min) | 84.72 (11.88) | 84.27 (10.94) | 84.58 (10.38) | 83.92 (11.58) | 0.8962 | 0.7912 |
| MAP (mmHg) | 77.30 (7.33) | 76.07 (6.84) | 75.83 (7.58) | 76.33 (5.90) | 0.0865 | 0.6858 |
| PWV (m/s) | 4.42 (0.85) | 4.36 (0.94) | 4.45 (1.17) | 4.26 (0.62) | 0.3693 | 0.5200 |
| Hypertension by SBP | 72 (23.08) | 38 (16.24) | 20 (16.00) | 18 (16.51) | 0.1029 | 0.9778 |
| Hypertension by DBP | 19 (6.09) | 10 (4.27) | 6 (4.80) | 4 (3.67) | 0.3905 | 0.9108 |
| Weight (kg)a | 35.31 (10.07) | 33.01 (7.50) | 32.77 (7.70) | 33.26 (7.30) | 0.0041 | 0.8633 |
| Height (cm) | 137.32 (7.61) | 137.03 (7.19) | 136.46 (7.22) | 137.67 (7.13) | 0.4588 | 0.4956 |
| Waist (cm)a | 65.77 (10.19) | 63.95 (8.56) | 63.64 (8.79) | 64.30 (8.32) | 0.0394 | 0.8216 |
| BMI (kg/m2)a | 18.52 (4.05) | 17.45 (2.95) | 17.46 (3.08) | 17.43 (2.82) | 0.0010 | 0.9987 |
| Obesitya | 84 (26.42) | 40 (17.08) | 23 (18.25) | 18 (15.79) | 0.0156 | 0.9087 |
| Weight z-scoresa | 0.49 (1.14) | 0.19 (0.99) | 0.17 (1.02) | 0.22 (0.97) | 0.0023 | 0.9415 |
| Height z-scores | 0.31 (1.03) | 0.17 (0.98) | 0.11 (0.96) | 0.25 (1.00) | 0.0703 | 0.6088 |
| BMI z-scoresa | 0.43 (1.19) | 0.15 (1.03) | 0.15 (1.04) | 0.14 (1.03) | 0.0068 | 0.9833 |
| Fat(kg)a | 7.66 (5.43, 11.47) | 6.89 (4.95, 9.94) | 6.74 (5.08, 9.90) | 6.90 (4.87, 9.97) | 0.0271 | 0.9237 |
| Lean Dry Mass (kg) | 5.40 (1.80) | 5.17 (1.79) | 5.28 (1.69) | 5.04 (1.89) | 0.1670 | 0.6802 |
| Bone Mineral Content (kg)a | 1.62 (0.53) | 1.50 (0.45) | 1.54 (0.42) | 1.45 (0.47) | 0.0057 | 0.4721 |
| Lean Soft Tissue (kg)a | 23.53 (5.26) | 22.19 (5.25) | 22.87 (4.62) | 21.46 (5.79) | 0.0071 | 0.2353 |
| Fat-Free Mass (kg) | 25.66 (5.13) | 24.84 (4.39) | 24.84 (4.45) | 24.84 (4.34) | 0.0569 | 1.0000 |
| Fat Mass Index (kg/m2) | 4.17 (2.89, 5.87) | 3.74 (2.65, 5.38) | 3.85 (2.69, 5.38) | 3.57 (2.50, 5.37) | 0.1099 | 0.9120 |
| Fat Free Mass Index (kg/m2)a | 13.54 (1.60) | 13.20 (1.36) | 13.28 (1.40) | 13.11 (1.31) | 0.0140 | 0.6573 |
N (%) unless unit specified in which case mean (SD) or median (IQR) shown
Note: Statistics were derived from all singletons and one randomly selected twin of each pair.
P<0.05 between treatment (first 2 columns);
P<0.05 between OI/IUI and ART (last 2 columns);
Missing data: marital status (n=5), maternal hypertension by SBP (n=13), maternal hypertension by DBP (n=13), maternal arterial stiffness (n=44), paternal BMI (n=29), age at visit (n=1); Missing data of childhood cardio metabolic risk: SBP (n=13), DBP (n=13), heart rate (n=13), MAP (n=14), PWV (n=63), weight (n=1), height (n=1), waist (n=9), BMI (n=1), fat (n=33), lean dry mass (n=38), bone mineral content (n=38), lean soft tissue (n=33), fat-free mass (n=64), fat mass index (n=33), fat free mass index (n=64)
Cardiovascular and Anthropometric Measures Among Singletons
Mean BP or PWV were similar among singletons regardless of mode of conception (Figure 1). Compared to singletons born following no treatment, singletons conceived by ART had higher odds of hypertension defined by elevated SBP (adjusted OR 2.14; 95%CI: 0.93, 4.91) but not when defined by DBP (1.02; 0.18, 5.71) (Table 2). With respect to anthropometry, singletons conceived by OI weighed less at the clinic visit (−3.25kg; −5.80, −0.70) and were shorter (−2.45cm; −4.28, −0.62) compared to singletons not conceived by treatment. They also had lower fat-free mass (−1.73kg; −3.09, −0.37) and fat free mass index (−0.46; −0.89, −0.02) as measured by BIA but not fat mass or fat mass index. Singletons conceived by ART also tended to be smaller with respect to the same measures. However, these differences should be interpreted with respect to normative size for age and sex as presented by z-scores (see Table 1) and suggest that differences in size may be driven by the larger than normative size among the singletons not conceived by treatment rather than that the singletons conceived by treatment had poorer growth than normal. Specifically, singletons conceived by OI/ART were smaller than singletons not conceived by treatment but the latter averaged higher BMI than national norms (i.e., mean 0.41 (SD 1.24) z-score for no treatment vs. 0.22 (1.02) for OI/IUI and 0.16 (1.10) for ART). Odds of obesity among singletons also did not differ by specific type of treatment.
Figure 1.
Fertility treatment and childhood cardiovascular measures. Mean differences (95% confidence intervals) in SBP, DBP, and PWV are compared between the fertility treatment groups designated against a reference group of children conceived without treatment. Singletons conceived with ART (n=50) or OI (n=63) were compared with singletons not conceived by treatment (n=220). Twins conceived with ART (n=64) or OI (n=63) were compared against twins not conceived by treatment (n=99). Solid symbols represent singletons, open symbols represent twins. Circles represent OI/IUI and triangles represent ART. Twins conceived by treatment had lower blood pressure than those conceived without treatment. However, twins conceived by OI/IUI had higher PWV. The dotted line at 0 represents the reference group of singletons or twins not conceived with fertility treatment.
Table 2.
Childhood cardio-metabolic risk by infertility treatment status (OI/IUI or ART vs. none) stratified by plurality, Upstate KIDS Study
| Singletons (OI/IUI vs. no) | Singletons (ART vs. no) | Twins (OI/IUI vs. no) | Twins (ART vs. no) | |
|---|---|---|---|---|
| N¥ | 63 | 50 | 63 | 64 |
| SBP (mmHg) | −1.56 (−4.35, 1.22) | 1.50 (−1.73, 4.73) | −5.13 (−8.79, −1.48)** | −5.86 (−9.91, −1.80)*** |
| DBP (mmHg) | −0.32 (−2.19, 1.54) | 0.89 (−1.27, 3.05) | −1.02 (−3.34, 1.30) | −3.01 (−5.71, −0.30)* |
| Heart rate | 2.83 (−0.42, 6.07) | 1.60 (−2.16, 5.36) | −3.61 (−8.34, 1.12) | −3.16 (−8.02, 1.70) |
| MAP (mmHg) | −0.73 (−2.76, 1.31) | 1.12 (−1.23, 3.48) | −2.21 (−4.81, 0.40) | −3.66 (−6.72, −0.60)* |
| PWV (m/s) | −0.14 (−0.40, 0.11) | −0.11 (−0.40, 0.18) | 0.59 (0.03, 1.15)* | 0.16 (−0.13, 0.45) |
| Hypertension by SBP (y/n) | 1.09 (0.50, 2.36) | 2.14 (0.93, 4.91) | Too few | Too few |
| Hypertension by DBP (y/n) | 1.16 (0.28, 4.76) | 1.02 (0.18, 5.71) | Too few | Too few |
| Weight (kg) | −3.25 (−5.80, −0.70)* | −2.08 (−5.03, 0.87) | −0.93 (−3.87, 2.01) | −1.43 (−4.38, 1.52) |
| Height (cm) | −2.45 (−4.28, −0.62)** | −1.73 (−3.85, 0.39) | 0.31 (−2.54, 3.17) | 0.80 (−2.12, 3.72) |
| Waist (cm) | −2.38 (−5.14, 0.37) | −0.36 (−3.54, 2.82) | −2.13 (−5.34, 1.09) | −2.16 (−5.59, 1.26) |
| BMI (kg/m2) | −1.03 (−2.07, 0.01) | −0.65 (−1.86, 0.55) | −0.51 (−1.61, 0.58) | −0.78 (−1.96, 0.40) |
| Obesity (y/n) | 0.74 (0.35, 1.57) | 1.05 (0.46, 2.42) | Too few | Too few |
| Weight z-scores | −0.38 (−0.68, −0.07)* | −0.26 (−0.62, 0.09) | −0.14 (−0.54, 0.26) | −0.07 (−0.48, 0.34) |
| Height z-scores | −0.39 (−0.67, −0.10)** | −0.27 (−0.60, 0.06) | 0.07 (−0.37, 0.51) | 0.15 (−0.29, 0.60) |
| BMI z-scores | −0.21 (−0.53, 0.11) | −0.16 (−0.53, 0.21) | −0.23 (−0.58, 0.13) | −0.22 (−0.62, 0.19) |
| Fat(kg) | −1.51 (−3.16, 0.14) | −0.76 (−2.66, 1.13) | 0.14 (−1.67, 1.96) | −0.54 (−2.29, 1.21) |
| Lean Dry Mass (kg) | −0.27 (−0.71, 0.18) | −0.14 (−0.65, 0.38) | −0.17 (−0.86, 0.52) | −0.03 (−0.72, 0.65) |
| Bone Mineral Content (kg) | −0.14 (−0.28, 0.00) | −0.09 (−0.25, 0.08) | 0.00 (−0.16, 0.15) | −0.04 (−0.20, 0.11) |
| Lean Soft Tissue (kg) | −1.22 (−2.49, 0.06) | −0.72 (−2.19, 0.74) | −0.40 (−2.24, 1.44) | −0.26 (−1.89, 1.37) |
| Fat-Free Mass (kg) | −1.73 (−3.09, −0.37)* | −1.18 (−2.77, 0.42) | −0.04 (−1.94, 1.85) | −0.41 (−2.21, 1.40) |
| Fat Mass Index | −0.61 (−1.42, 0.20) | −0.29 (−1.22, 0.65) | 0.22 (−0.85, 1.29) | −0.11 (−1.15, 0.93) |
| Fat Free Mass Index | −0.46 (−0.89, −0.02)* | −0.41 (−0.92, 0.10) | −0.04 (−0.60, 0.52) | −0.15 (−0.64, 0.34) |
Adjusted for age at the visit, sex, maternal race, maternal education, plurality, maternal age, site, private insurance and pre-pregnancy BMI. Estimate (95% CI) presents betas for continuous outcomes and odds ratios for binary outcomes.
Singletons conceived with ART (n=50) or OI (n=63) were compared with singletons not conceived by treatment (n=220). Twins conceived with ART (n=64) or OI (n=63) were compared against twins not conceived by treatment (n=99).
P-value < 0.05.
P-value < 0.01.
P-value < 0.005.
Cardiovascular and Anthropometric Measures Among Twins
Twins conceived with fertility treatment had lower blood pressure compared to twins conceived using no treatment (e.g., adjusted SBP difference for OI twins: −5.13mmHg (−8.79, −1.48) and for ART twins: −5.86mmHg (−9.91, −1.80)). However, OI twins had significantly higher arterial stiffness (0.59; 0.03, 1.15 m/s) with no significant difference observed among ART twins (0.16m/s; −0.13, 0.45) (Table 2). Adjustment for maternal PWV attenuated the differences in child PWV (among OI: 0.29m/s; −0.03, 0.60). Otherwise, findings were similar regardless of model covariates including additional adjustment for paternal BMI and maternal cardiovascular measures (Supplemental Table 2). There was a tendency for twins born following fertility treatment to be smaller by weight and thinner by waist circumference and BMI than twins born following no treatment, but differences were minimal (Table 2).
Cardio-metabolic Biomarkers
Distributions of biomarkers are provided in Supplemental Table 3. No statistically significant differences in mean levels of lipids, HbA1c, and CRP measures were observed by mode of conception (Table 3). Results were also similar after stratifying on plurality (data not shown). By national guidelines on pediatric dyslipidemia, there were 10 children with non-HDL cholesterol ≥ 145 mg/dl, 17 with HDL<40 mg/dl and 24 children by either cutoff. The incidence of dyslipidemia was nearly identical across groups: (14 [9%] no treatment, 4 [9%] ART, 5 [8%] OI).
Table 3.
Mean differences (95% confidence Intervals) of childhood cardio-metabolic biomarkers by mode of conception, Upstate KIDS Study
| Infertility treatment (any) | p-value | ART | p-value | OI | p-value | |
|---|---|---|---|---|---|---|
| N | 108 | 44 | 64 | |||
| Total cholesterol (mg/dl) | 2.25 (−3.95, 8.45) | 0.48 | 4.75 (−2.82, 12.31) | 0.22 | 0.60 (−7.02, 8.23) | 0.88 |
| HDL cholesterol (mg/dl) | 0.25 (−3.27, 3.78) | 0.89 | 1.94 (−3.19, 7.07) | 0.46 | −0.87 (−4.41, 2.68) | 0.63 |
| LDL cholesterol (mg/dl) | 1.94 (−3.53, 7.41) | 0.49 | 4.59 (−2.72, 11.89) | 0.22 | 0.16 (−6.41, 6.74) | 0.96 |
| Non-HDL cholesterol (mg/dl) | 1.87 (−4.37, 8.12) | 0.56 | 2.82 (−5.10, 10.74) | 0.49 | 1.25 (−6.48, 8.98) | 0.75 |
| CRP (mg/L) | −0.05 (−0.59, 0.48) | 0.84 | 0.10 (−0.75, 0.94) | 0.82 | −0.18 (−0.73, 0.38) | 0.53 |
| HbA1c (%) | 0.01 (−0.06, 0.07) | 0.87 | −0.02 (−0.12, 0.07) | 0.61 | 0.02 (−0.05, 0.10) | 0.53 |
Reference group included 155 children conceived without treatment.
Adjusted for age at the visit, sex, maternal race, maternal education, plurality, maternal age, site, private insurance and pre-pregnancy BMI. HbA1c models additionally adjusted for maternal HbA1c.
Discussion
In this first U.S. population-based study to evaluate blood pressure differences in both singletons and twins conceived by fertility treatment, we found no evidence of a link between conception via ART and blood pressure elevation in middle childhood. Differences observed in children conceived by OI also suggest no consistent detrimental cardiovascular impact of fertility treatment. Analyses of cardio-metabolic biomarkers (e.g., CRP) were consistent with the general lack of differences between children by mode of conception.
ART and Cardio-metabolic Risk
Most studies published since the 2017 meta-analysis of cardiovascular health in ART in children (11) found no differences in blood pressure or PWV (20) and only selected differences in other cardio-metabolic risk factors whether in middle childhood (12, 13) or older age (14–18). However, a recent study of 6–10 year old singletons (n=382 ART and 382 no treatment) observed substantially higher adjusted mean SBP (2.0 mmHg; 95%CI: 0.9 to 3.0) and DBP (5.0 mmHg; 95%CI: 4.1 to 5.8) by ART even though their children were conceived between 2007–2013.(19) Differences were also noted in measures not made in the current study (e.g., left ventricular mass and function, higher fasting glucose, insulin resistance, and carotid intima-media thickness). Blood pressure findings seemed unrelated to perinatal differences between their two groups, as they observed no differences in gestational age or proportion born preterm, and if anything birthweight was 80g higher among children conceived by ART than not. While the authors acknowledged that the differences observed may have limited clinical significance given that blood pressure levels were still in the normal range, such large shifts in population mean differences of blood pressure could still translate to substantial cardiovascular outcomes in adulthood. Their finding, which runs counter to most studies including ours, require replication. However, some indication that ART practices substantially differ depending on country/practice was suggested, as their use of ICSI was 34% compared to the much higher proportion in the US (1, 33).
Heterogeneity of findings between studies, including period differences in outcomes noted by the previous meta-analysis (11), may be explained by technological practices in ART. Historically, the first in vitro fertilization successes in 1978 and 1980 by Edwards and Steptoe were completed under natural cycle and had <1% success due to the inability to overcome the issue of uterine receptivity after hormonal stimulation (34). Records kept at that time reveal varying “recipes” of nutrients were tested for embryo culture including maternal sera and paternal seminal plasma, along with changes in osmolarity and pH (35). Later on, sequential media came to be used after the struggles in the 1990s with embryo culture which may explain these period effects (36). Hence, more recent IVF may not be comparable to earlier IVF (especially when also considering the introduction of ICSI). Under the Developmental Origins hypothesis, all of these practices have potential to affect long-term health. Hence, suboptimal conditions around the periconception period in ART remain a struggle, bolstering the need to continue to evaluate technologies and ongoing practices.
OI and Cardio-metabolic Risk
Studies on cardio-metabolic risk among children conceived by fertility drugs without IVF/ICSI are few. One randomized trial from the Netherlands followed children conceived with controlled ovarian hyperstimulation with IUI (n=63), modified IVF (n=53) or “regular” IVF with SET (n=70) to test the impact of hormonal stimulation with or without embryo culture (37). BMI, body fat, blood pressure, PWV, lipids and glucose/insulin did not differ among the 3 groups. As a randomized trial, this study was less subject to confounding, although selection in terms of live-birth success by the three methods cannot be ruled out. The Groningen ART cohort also observed no differences by ovarian hyperstimulation on measures (12). Our findings showing no difference among singletons are in line with these observations. However, one study of 5–6 year old children found that OI was associated with higher blood pressure (i.e., 2.7; 0.2, 5.2 mmHg SBP, and 3.1; 1.0, 5.2 mmHg DBP) and triglycerides (0.1; 0, 0.3 mmol/l) but no differences in anthropometry (38). Hence, of the four studies including our own, the majority have not found a difference in cardio-metabolic health indicators, but more could be done with larger sample sizes to tease apart the impact by the type of ovarian stimulation.
Strengths & Limitations
Our study was strengthened by the comprehensive evaluation of cardio-metabolic risk, objectively assessed by trained examiners and was able to account for important confounders including maternal BMI and blood pressure. PWV and BIA measures and serum biomarkers provided a particularly robust assessment of cardio-metabolic risk. We were able to account for important confounders including parental BMI and blood pressure. Nevertheless, pediatric assessments of blood pressure are not trivial. While we observed elevated PWV in OI twins, this observation is incongruous with having lower blood pressure. One rationale could be that the OI twins were more able to comply with the supine measure of PWV than with sitting still for lengthy periods especially while the sibling is around. However, it’s not clear why that would not be so with ART twins. The study was also limited by the number of families living in proximity to the study sites, willingness of families to participate in general, and agreement of children to participate in a blood draw. Tracing suggested very few families were lost to follow-up and that the majority passively did not respond to the clinic invitation. While the children were still relatively young, pubertal status was not captured and accounted for. Specifically, for girls, pubertal onset may begin from 8 years of age and for boys from 9–10 years of age (39). Lastly, the cohort is predominantly non-Hispanic White and the age of the children meant that we were assessing early-onset (and therefore likely more severe) cardio-metabolic risk which may limit generalizability.
In conclusion, conception by ART or OI did not increase cardio-metabolic risk indicators in middle childhood age groups. While risks may reveal themselves after puberty ensues, these findings are reassuring considering the early reports of elevated blood pressure and subclinical CVD measures. The specific underlying causes of infertility (e.g., polycystic ovarian syndrome) that led to the need for treatment deserve further investigation. Ongoing studies may be necessary to tease apart differences in ever evolving ART techniques.
Supplementary Material
Supplemental Figure 1. Study participant sample size flowchart, Upstate KIDS
Acknowledgements
The authors thank the Upstate KIDS participants and staff for their important contributions. The authors also thank all the members of SART for providing clinical information to the SART Clinic Outcome Reporting System database for use by patients and researchers.
Funding Source:
Supported by the Intramural Research Program of the Eunice Kennedy Shriver National Institute of Child Health and Human Development (NICHD; contracts #HHSN275201200005C, #HHSN267200700019C, #HHSN275201400013C, #HHSN275201300026I/27500004, #HHSN275201300023I/27500017).
Footnotes
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Associated Data
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Supplementary Materials
Supplemental Figure 1. Study participant sample size flowchart, Upstate KIDS