The growth of twins between the ages of 2 and 9 years

Growth of twins conceived using assisted reproductive treatments up to 5 years old: a national growth cohort

STUDY QUESTION

Do twins conceived through assisted reproductive treatments (ART) grow differently from naturally conceived (NC) twins in early life?

SUMMARY ANSWER

Assessments at 6-8 weeks old and at school entry show that ART twins conceived from frozen embryo transfer (FET) grow faster than both NC twins and ART twins conceived from fresh embryo transfer (ET).

WHAT IS KNOWN ALREADY

Singletons born from fresh ET grow more slowly in utero and in the first few weeks of life but then show postnatal catch-up growth by school age, compared to NC and FET babies. Evidence on early child growth of ART twins relative to NC twins is inconsistent; most studies are small and do not distinguish FET from fresh ET cycles.

STUDY DESIGN, SIZE, DURATION

This cohort study included 13 528 live-born twin babies conceived by ART (fresh ET: 2792, FET: 556) and NC (10 180) between 1991 and 2009 in Scotland. The data were obtained by linking Human Fertilisation and Embryology Authority ART register data to the Scottish Morbidity Record (SMR02) and Scottish child health programme datasets. Outcome data were collected at birth, 6-8 weeks (first assessment), and school entry (4-7 years old) assessments. The primary outcome was growth, measured by weight at the three assessment points. Secondary outcomes were length (at birth and 6-8 weeks) or height (at school entry), BMI, occipital circumference, gestational age at birth, newborn intensive care unit admission, and growth rates (between birth and 6-8 weeks and between 6-8 weeks and school entry).

PARTICIPANTS/MATERIALS, SETTING, METHODS

All twins in the linked dataset (born between 1991 and 2009) with growth data were included in the analysis. To determine outcome differences between fresh ET, FET, and NC twins, linear mixed models (or analogous logistic regression models) were used to explore the outcomes of interest. All models were adjusted for available confounders: gestational age/child age, gender, maternal age and smoking, Scottish Index of Multiple Deprivation, year of treatment, parity, ICSI, and ET stage.

MAIN RESULTS AND THE ROLE OF CHANCE

In the primary birth weight models, the average birth weight of fresh ET twins was lower [-35 g; 95% CI: (-53, -16)g] than NC controls, while FET twins were heavier [71 g; 95% CI (33, 110) g] than NC controls and heavier [106 g; 95% CI (65, 146) g] than fresh ET twins. However, the difference between FET and NC twins was not significant when considering only full-term twins (≥37 weeks gestation) [26 g; 95% CI (-30, 82) g], while it was significantly higher in preterm twins [126 g; 95% CI (73, 179) g]. Growth rates did not differ significantly for the three groups from birth to 6-8 weeks. However, FET twins grew significantly faster from 6 to 8 weeks than NC (by 2.2 g/week) and fresh ET twins (by 2.1 g/week). By school entry, FET twins were 614 g [95% CI (158, 1070) g] and 581 g [95% CI (100, 1063) g] heavier than NC and fresh ET twins, respectively. Length/height and occipital frontal circumference did not differ significantly at any time point.

LIMITATIONS, REASONS FOR CAUTION

Although the differences between ART and NC reflect the true ART effects, these effects are likely to be mediated partly through the different prevalence of mono/dizygotic twins in the two groups. We could not explore the mediating effect of zygosity due to the unavailability of data. The confounding variables included in the study were limited to those available in the datasets.

WIDER IMPLICATIONS OF THE FINDINGS

Live-born twins from FET cycles are heavier at birth, grow faster than their fresh ET and NC counterparts, and are still heavier at school entry. This differs from that observed in singletons from the same cohort, where babies in the three conception groups had similar weights by school entry age. The results are reassuring on known differences in FET versus fresh ET and NC twin outcomes. However, FET twins grow faster and are consistently larger, and more ART twins depict catch-up growth. These may lead to an increased risk profile for non-communicable diseases in later life. As such, these twin outcomes require careful evaluation using more recent and comprehensive cohorts.

STUDY FUNDING/COMPETING INTEREST(S)

This study was funded by the EU H2020 Marie Sklodowska-Curie Innovative Training Networks (ITN) grant Dohartnet (H2020-MSCA-ITN-2018-812660). The authors have no competing interests to declare.

TRIAL REGISTRATION NUMBER

N/A.

Developmental origins of cardiometabolic health outcomes in twins: A systematic review and meta-analysis

BACKGROUND AND AIMS

Studies of twins can reduce confounding and provide additional evidence about the causes of disease, due to within-pair matching for measured and unmeasured factors. Although findings from twin studies are typically applicable to the general population, few studies have taken full advantage of the twin design to explore the developmental origins of cardiometabolic health outcomes. We aimed to systematically review the evidence from twin studies and generate pooled estimates for the effects of early-life risk factors on later-life cardiometabolic health.

METHODS AND RESULTS

An initial search was conducted in March 2018, with 55 studies of twins included in the review. Risk of bias was assessed using the Newcastle-Ottawa Scale, and eligible studies were included in a meta-analysis, where pooled estimates were calculated. Twenty-six studies analysed twins as individuals, and found that higher birthweight was associated with lower SBP (β = -2.02 mmHg, 95%CI: -3.07, -0.97), higher BMI (β = 0.52 kg/m², 95%CI: 0.20, 0.84) and lower total cholesterol (β = -0.07 mmol/L, 95%CI: -0.11, -0.04). However, no associations were reported in studies which adjusted for gestational age. Few of the included studies separated their analyses into within-pair and between-pair associations.

CONCLUSIONS

Early-life risk factors were associated with cardiometabolic health outcomes in twin studies. However, many estimates from studies in this review were likely to have been confounded by gestational age, and few fully exploited the twin design to assess the developmental origins of cardiometabolic health outcomes.

Different levels of cardiometabolic indicators in multiple vs. singleton children

BACKGROUND

We aimed to compare cardiometabolic indicators in singletons and multiples at age 7 and explore the birthweight mediation effect.

METHODS

We studied 5431 singletons and 103 sets of multiples from Generation XXI birth cohort. Anthropometric measurements, body composition, and fasting blood samples were obtained. Age- and sex-specific z-scores were calculated (additionally height-specific for blood pressure). Adjusted regression coefficients and respective 95% confidence intervals [β (95%CI)] were computed using path analysis.

RESULTS

Multiples had lower weight [- 0.419 (- 0.616;-0.223)], height [- 0.404 (- 0.594;-0.213)], BMI [- 0.470 (- 0.705;-0.234)], fat mass index [- 0.359 (- 0.565;-0.152)], waist circumference [- 0.342 (- 0.537;-0.147)], and waist-to-height ratio [- 0.165 (- 0.326;-0.003)] z-scores. These results were explained by the indirect effect via birthweight, which was also negative and significant for all the aforementioned cardiometabolic indicators, while no direct effect was present. There were also significant indirect effects regarding fat-free mass index, glucose, insulin, and blood pressure, though the total effects were not significant, due to the balance between direct and indirect effects. The only significant direct effect was regarding diastolic blood pressure [- 0.165 (- 0.302;-0.028)].

CONCLUSIONS

At age 7, multiples presented better cardiometabolic indicators explained by lower weight at birth, except for the lower blood pressure which was independent of an effect via birthweight.

Twin's Birth-Order Differences in Height and Body Mass Index From Birth to Old Age: A Pooled Study of 26 Twin Cohorts Participating in the CODATwins Project

We analyzed birth order differences in means and variances of height and body mass index (BMI) in monozygotic (MZ) and dizygotic (DZ) twins from infancy to old age. The data were derived from the international CODATwins database. The total number of height and BMI measures from 0.5 to 79.5 years of age was 397,466. As expected, first-born twins had greater birth weight than second-born twins. With respect to height, first-born twins were slightly taller than second-born twins in childhood. After adjusting the results for birth weight, the birth order differences decreased and were no longer statistically significant. First-born twins had greater BMI than the second-born twins over childhood and adolescence. After adjusting the results for birth weight, birth order was still associated with BMI until 12 years of age. No interaction effect between birth order and zygosity was found. Only limited evidence was found that birth order influenced variances of height or BMI. The results were similar among boys and girls and also in MZ and DZ twins. Overall, the differences in height and BMI between first- and second-born twins were modest even in early childhood, while adjustment for birth weight reduced the birth order differences but did not remove them for BMI.

Longitudinal growth and body composition of twins versus singletons in the first month of life

Background. Although twin gestation is well recognized to be associated with impaired fetal and postnatal growth, specific data about body composition of twins in the first month of life are scarce. Objective. The aim of this study was to compare the body composition of twins, evaluated with air-displacement plethysmography, to that of singletons of similar gestational age and adequacy of growth, during the first month of life. We tested the hypothesis that the quality of growth would be similar. Methods. Anthropometric and air-displacement plethysmography measurements were performed in 18 pairs of twins and in 36 singleton neonates, longitudinally, from birth to the 30th day of life. Each twin was matched to a singleton infant of similar gestational age and birth weight z-score. Results. With regard to anthropometric measures, the only difference was a lower weight in twins versus singletons on the 15th day of life. With regard to body composition, we did not find any difference between groups at any time point. Fat mass increased significantly from day 1 to day 30 in both twins and singletons. Conclusion. In terms of body composition, twins do not differ from singletons of similar gestational age and weight, either at birth or in early postnatal life.

Adult body height of twins compared with that of singletons: a register-based birth cohort study of Norwegian males

In the present study, we evaluated whether childhood differences in body height between singletons and twins persist into adulthood. Data from the Medical Birth Register of Norway were linked with data from the Norwegian National Conscript Service. This study used data on the 457,999 males who were born alive and without physical anomalies in single or twin births in Norway during 1967-1984 and who were examined at the mandatory military conscription (age 18-20 years; 1985-2003). For sibling comparisons, the authors selected the 1,721 sibships of full brothers that included at least 1 male born in a single birth and at least 1 male born in a twin birth (4,520 persons, including 2,493 twins and 2,027 singletons). An analysis of the total study population using generalized estimating equations showed that the twins were 0.6 cm (95% confidence interval: 0.4, 0.7) shorter than were the singletons after adjustment for a series of background factors. The fixed-effects regression analysis of the sibships that included both twins and singletons showed that the twins were 0.9 cm (95% confidence interval: 0.6, 1.2) shorter than were their singleton brothers. The study suggests that male twins born in Norway during 1967-1984 were slightly shorter in early adulthood than were singletons.

Weight growth of triplet infants from birth to twelve years of age

We analyzed the characteristics associated with the growth in weight of Japanese triplets from birth to 12 years of age. The study included 376 mothers and their 1,128 triplet children, who were born between 1978 and 2006. Data were collected through a mailed questionnaire sent to the mothers asking for information recorded in medical records. For these births, data on triplets' weight growth, gestational age, sex, parity, maternal age at delivery, maternal height, and maternal body mass index were obtained from records in the Maternal and Child Health Handbooks and records in the school where children receive health check-ups. The weight deficit of the triplets compared to the general population of Japan remained between 10% and 17% until 12 years of age. Moreover, at 12 years of age, the differences of weight between the general population and triplets were approximately -4.75 kg for boys and -6.00 kg for girls. Very low birth weight had the strongest contribution to body weight until 8 years of age. After 8 years of age, maternal body mass index was a significant factor affecting the weight of triplets until 12 years of age.

Lactase persistence and milk consumption are associated with body height in Swedish preadolescents and adolescents

BACKGROUND

Body height is a classic polygenic trait. About 80%-90% of height is inherited and 10%-20% owed to environmental factors, of which the most important ones are nutrition and diseases in preadolescents and adolescents.

OBJECTIVE

The aim of this study was to explore potential relations between the LCT (lactase) C>T-13910 polymorphism, milk consumption, and body height in a sample of Swedish preadolescents and adolescents.

DESIGN

In a cross-sectional study, using a random sample of preadolescents and adolescents (n = 597), dietary intakes were determined. Anthropometric measurements including sexual maturity (Tanner stage) and birth weight were assessed. Parental body height and socio-economic status (SES) were obtained by questionnaires. Genotyping for the LCT C>T-13910 polymorphism that renders individuals lactase persistent (LP) or lactase non-persistent (LNP) was performed by DNA sequencing. Stepwise backward multivariate linear regression was used.

RESULTS

Milk consumption was significantly and positively associated with body height (β = 0.45; 95% CI: 0.040, 0.87, p = 0.032). Adjustments were performed for sex, parental height, birth weight, body mass index (BMI), SES, and Tanner stage. This model explains 90% of the observed variance of body height (adjusted R(2) = 0.89). The presence of the -13910 T allele was positively associated with body height (β = 2.05; 95% CI: 0.18, 3.92, p = 0.032).

CONCLUSIONS

Milk consumption is positively associated with body height in preadolescents and adolescents. We show for the first time that a nutrigenetic variant might be able to explain in part phenotypic variation of body height in preadolescents and adolescents. Due to the small sample size further studies are needed.

Birth weight discordance of twin pairs and their subsequent growth patterns

BACKGROUND

Few studies have compared the growth of a twin with its co-twin and particularly in relation to birth weight discordance.

AIM

The study investigated how the degree of birth weight discordance affected subsequent growth.

METHODS

Birth weight discordance of 762 twin pairs was determined. Subsequent weight, height and occipital-frontal head circumference (OFC) measurements were obtained between the ages of 2-9 years. Corresponding standard deviations scores (SDS) were analysed according to birth weight discordance, sex and zygosity. Weight status was taken into account by assigning twins into sub-groups according to whether they were the heavier twin at birth and remained heavier, became the lighter of the twin pair or had the same weight, for subsequent measurements.

RESULTS AND CONCLUSIONS

The degree of birth weight discordance had little effect on subsequent growth except in monozygotic (MZ) twins with >20% discordance. Severe low birth weight ( < 1.95 kg) is more significant in suppressing subsequent growth than the degree of discordance per se. A surprisingly high proportion of twins reversed their weight status when reviewed at an older age.

Parental mental health and child development from six to thirty-six months in a birth cohort study in Taiwan

This study investigated the reciprocity between parental mental health and the different stages of child development at 6, 18, and 36 months. As the pilot of a birth cohort study, this study comprised 2048 children and their parents who were randomly selected and invited to participate. The development of these children and the mental health of their parents were followed at 6, 18, and 36 months postpartum. Child development was assessed using the Taiwan Birth Cohort Study instrument, and parental health was assessed using the Taiwanese version of the 36-Item Short Form Health Survey. Complete responses for all three stages were received from 844 families. Our results showed that parental mental health had a direct effect on language and social development; however, this effect did not become significant until 36 months. The reciprocity between child development and parental mental health and proper intervention are vital.

Health care supervision for twin pairs

Twins are at increased risk for congenital anomalies and have particular health care needs, but twin management guidelines do not exist. This review attempts to integrate the latest research findings and evidence-based medicine on twins into basic clinical recommendations for general pediatricians.

Twin-singleton influence on infant development: a national birth cohort study

BACKGROUND

While studying the development of twins, gestational age and birthweight were suggested as two of the major mediators to be considered. In addition, maternal age, maternal education, parental income and assisted reproductive technologies (ART) also should be considered as moderators. Thus the purpose of this study was to investigate the mediators and moderators of twin and singleton development.

METHODS

Being a national birth cohort study, 21 648 infants were randomly selected and developmental measures were assessed at 6 and 18 months post partum. Children's development at 6 and 18 months were measured using the high reliable Taiwan Birth Cohort Study instrument, which measures children's development in four domains of gross motor, fine motor, language and social development. Additionally, maternal sociodemographics including maternal age, maternal education and parental income; children's characteristics including gender, birthweight, gestational age, single or multiple births, ART or natural conception information were also collected. These data were analysed using a three-step multiple linear regression analysis and further validated using structural equation modelling.

RESULTS

Parental sociodemographics, children characteristics and being twin all had effect on children's development. Additionally, ART and twin were mediators between maternal age and children's development. Mothers aged over 40 were more likely to choose ART, thus increases their likelihood of having twins. Additionally, mothers aged over 40 were more likely to give birth to premature or low-birthweight babies, regardless if they were twin or not. Twins had a higher prevalence of prematurity or low birthweight, which also affected their development in all four domains at 6 and 18 months. Thus prematurity and low birthweight were mediating factors between twin and children's development; with these two mediating factors controlled, there were no difference between twin and singleton development.

CONCLUSIONS

The conceptual construct of structural equation modelling showed these factors interacted and influenced children's development through multiple pathways. Medical intervention may facilitate children's development through prenatal growth and premature care.