Growth and development in premature twins

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.

Pre- and Perinatal Characteristics Associated with Apgar Scores in a Review and in a New Study of Dutch Twins

A literature review was carried out to identify pre and perinatal characteristics associated with variation in Apgar scores in population-based studies. The parameters identified in the literature search were included in the classical twin design study to estimate effects of pre and perinatal factors shared and nonshared by twins and to test for a contribution of genetic factors in 1- and 5-min Apgar scores in a large sample of Dutch monozygotic (MZ) and dizygotic (DZ) twins. The sample included MZ and DZ twins (N = 5181 pairs) recruited by the Netherlands Twin Register shortly after birth, with data on prenatal characteristics and Apgar scores at first and/or fifth minutes. The ordinal regression and structural equation modeling were used to analyze the effects of characteristics identified in the literature review and to estimate genetic and nongenetic variance components. The literature review identified 63 papers. Consistent with the review, we observed statistically significant effects of birth order, zygosity and gestational age (GA) for 1- and 5-min Apgar scores of both twins. Apgar scores are higher in first-born versus second-born twins and DZ first-born versus MZ first-born twins. Birth weight had an effect on the 5-min Apgar of the first born. Fetal presentation and mode of delivery had different effects on Apgar scores of first- and second-born twins. Parental characteristics and chorionicity did not have significant main effects on Apgar scores. The MZ twins' Apgar correlations equaled the DZ Apgar correlations. Our analyses suggest that individual differences in 1- and 5-min Apgar scores are attributable to shared and nonshared pre and perinatal factors, but not to genotypic factors of the newborns. The main predictors of Apgar scores are birth order, zygosity, GA, birth weight, mode of delivery and fetal presentation.

Influences on Achieving Motor Milestones: A Twin–Singleton Study

In order to determine if twinning impacted achievement of motor milestones the attainment of early motor milestones in twins was examined and compared to published data from singletons of the same age from the same culture and birth years. We examined the influence of twinning, sex, zygosity and birth cohort (1987–2001) on the motor development of twins aged 0 to 24 months. Data on the attainment of motor milestones (turn, sit, crawl, stand and walk) of twins were collected from maternal reports. All data were corrected for gestational age. Data from the twin sample were compared to normative data from singletons, which were available from Child Health Clinics (CHC). Analyses across twin data and the CHC singleton data revealed no differences between twins and singletons in achievement of motor milestones. Girls were able to sit without support slightly earlier than boys, otherwise there were no other sex differences. Birth-order analyses revealed minimal but significant differences in turning over from back to belly and for sitting without support between the first- and second-born. Dizygotic (DZ) twins were faster than monozygotic (MZ) twins in achieving the moment of sit, crawl, stand and walk. Twins born in earlier cohorts were faster in reaching the moment of crawl, sit and walk. It is concluded that there are no differences in time of reaching motor milestones between twins and singletons within the normal range. Sex has minimal to no effect on motor development in early childhood. DZ twins achieve motor milestones sooner than MZ twins. Attainment of gross motor milestones (crawl, stand and walk) is delayed in later birth cohorts.

Comparison of motor development between twins and singletons in Japan: a population-based study

This study was performed using population-based data to analyze whether motor development in early life is different between singletons and twins in Japan. For better comparison and investigation, we divided the 2 groups into a group with a birthweight of 2.5 kg or greater (subgroup A) and a group with a birthweight of less than 2.5 kg (subgroup B), respectively. We analyzed the database of medical check-ups for children aged 3 years between April 2001 and July 2004. They received medical checkups at 4 months, 1.5, and 3 years of age. Children who were suspected of having neurological abnormality or disability were referred to specialists and excluded from the database. The data of 14,132 children were analyzed. Among these, 13,040 (92.3%) children were singletons in subgroup A, 75 (0.5%) were twins in subgroup A, 866 (6.1%) were singletons in subgroup B and 151 (1.1%) were twins in subgroup B. The mean age at achieving milestones was slower in twins of subgroup A for each developmental outcome than singletons of subgroup A, and the difference between twins and singletons was significant after adjustment for rolling over. On the contrary, after adjusting for a confounding factor (gestational age), singletons of subgroup B attained motor development facilitating walking independently slower than twins of subgroup B. There were different tendencies in the results regarding the motor development of subjects of subgroup A and that of subjects of subgroup B.

Two methods for estimating age of newborns in catch-up growth studies

Catch-up growth has been the subject of many studies, but whether and when infants born preterm and with low birth weight achieve normal size is controversial. One of the reasons for diverse results is likely to be the difference in how the infants' ages are calculated. The aim of this work is to analyse the occurrence and chronological distribution of compensational events of 163 infants born preterm conducted according to both chronological and corrected age. Catch-up growth was defined as the compensation of body weight values to those included between +/-1 SD in the reference system. Data were analysed using the survival analysis. Catch-up growth events were observed in greater amount for gestation-adjusted age. The correction of age allows the indication of the age, corresponding to the correct time of birth, as the time of the most rapid growth velocity. Chronological age does not allow any particular time to be distinguished as the most characteristic moment for achievement of constitutional growth. Within the whole studied period there is a similar probability of growth equalisation. A description of the morphological development of preterm infants should not be made in comparison to the postnatal reference system without correction of age, but analyses considering chronological age are necessary when the influence of gestational age is considered.

Physical and mental development of Turkish twins

BACKGROUND

Multiple gestations are known to bring some risks in the prenatal and natal period, but whether it is a risk for development in childhood is a matter of debate. The aim of the present study was to evaluate physical and mental development of Turkish twins and then to assess whether being a twin poses risks for their development.

METHODS

Fifty-two twin pairs (104 children) aged between 1 and 5 years were enrolled in the study. The control group consisted of 91 singletons, who were matched according to age, sex, gestational week and maternal educational level. The Denver Developmental Screening Test (DDST) was administered to assess cognitive development. Student t-test and chi2 test were used to compare the two groups.

RESULTS

The mean age of the mothers of twins did not differ from that of singleton mothers (P > 0.05). Twins were more frequently born in cases of assisted fertilization and were more often born via cesarean section. The birthweights of twins were lower and they were more frequently hospitalized after birth. The breast feeding period was shorter in twins and they had more chronic diseases than singletons (P < 0.05). Mothers of twins needed more help while caring for their infants. Physical development of twins and singletons did not differ statistically (P > 0.05). Twins had more suspect and delayed results in the DDST, especially in the language section of the test.

CONCLUSION

Physical and mental development of twins does not differ significantly from singletons except that twins might have a tendency towards slow language acquisition.

Developmental outcome of discordant premature twins at 3 years

BACKGROUND

There are numerous known or unknown maternal, fetal and intrauterine conditions that may lead to growth restriction. In addition to prematurity and growth restriction, developmental outcome may also be influenced by many genetic and environmental factors.

AIM

To examine the impact of intrauterine growth restriction on development in premature discordant twins.

STUDY DESIGN

Intra-pair control comparison.

METHODS

Developmental outcome at age 3 years was examined in 21 pairs of discordant (>15% birth weight discordance) very low birth weight (VLBW) premature twins.

RESULTS

None of the smaller twins had cerebral palsy and one larger twin had a mild diplegia. In paired comparisons, the smaller twins were somatically smaller and had a slight lower Griffiths' developmental quotient (GQ) than the co-twins without cerebral palsy [mean+/-S.D. 100+/-13, range 73-117, versus 104+/-12, 80-124, p=0.002]. The largest difference was in the locomotor subscale. There was a greater intra-pair GQ difference in the 12 twin pairs who had a discordance of greater than 30% (mean GQ=98 versus 105, p<0.001). The intra-pair GQ correlated well (r=0.90), a finding similar to that of a comparative group of 26 nondiscordant VLBW twin pairs (r=0.87). A multivariate analysis confirmed that gestation and percentage discordance were the important factors influencing GQ.

CONCLUSION

There exists a strong influence of common intrauterine, genetic and environmental factors on developmental outcome. Despite an overall lack of adverse outcome in smaller twins, results indicated a small but significant influence of growth restriction.

Neuromaturation of multiples

Etiology of preterm birth and degree of maturation are the primary determinants of a preterm infant's survival and complications. Multiple gestation increases the likelihood of preterm birth but its influence on rate of maturation or complications of prematurity has been controversial, primarily because of confounding variables (e.g. race, aetiology of preterm delivery, degree of prematurity and pregnancy complications). Very low birthweight preterm multiples have virtually the same rates of neonatal mortality, complications and neuromaturation as preterm singletons of the same gestational age. There is no advantage of delivering twins or higher order multiples before 30 weeks gestation, unless a fetus decompensates in utero. Survival improves for near term intermediate-size preterm multiples while intrauterine growth decelerates and placental and fetal neuromaturation accelerate. These data and the high fetal death rate at term support delivery of multiples as soon as there is fetal lung maturity, and consideration of elective delivery of twins at 35-38 weeks gestation and triplets at 33-35 weeks gestation.

Cognitive development and behaviour in very low birthweight twins at four years

This study included two groups of 37 children, one of twins and the other singletons at 4 years of age. All subjects has birthweights under 1500 grams and individuals in the groups were matched for birth date, gender and birthweight. Except when parental socio-economic status was taken into account, no significant differences between twins and singletons were observed on any of the results of The Stanford-Binet Intelligence Scale, nor were there any when the twins and singletons were divided into groups with birthweights < 1000 grams and 1000 to 1499 grams. When cognitive scores were analysed in relation to socio-economic status, there were significant differences in the whole population between subjects in the high and low socioeconomic status groups, with higher mean scores for the former. Comparison of the twins and singletons with parents in the lower socio-economic status group did not produce any significant differences but in the case of the upper socio-economic status group the singletons scored significantly better than the twins in Quantitative Reasoning and on the Composite Score. No significant differences were demonstrated in the clinical assessment of speech, language or behaviour. So far as general life considerations and health were concerned only one significant difference was found and this was for the number of siblings born subsequently, with more born in the singleton families. This study did not provide support for the view that singletons and twins differ significantly in the areas considered.