The relationship between maternal birthweight and gestational age in twins and singletons and those of their offspring in Norway

In order to elucidate whether maternal plurality affects offspring intrauterine growth, the relationship between birthweight and gestational age of twins and singletons and those of their first singleton liveborn children in Norway was studied using data from the Medical Birth Registry. The population-based sample consisted of 49 698 mother–offspring pairs (48 842 with singleton and 856 with twin-mothers). In bivariate analyses, no significant differences in mean birthweight and gestational age of offspring of twin and singleton mothers were found, although the mean birthweight and gestational age of the twin-mothers themselves were significantly lower than those of singletons (819 g and 14 days respectively). In multiple regression analysis, the expected birthweight of offspring was 230.3 g (95% CI: 193.2–267.4 g) higher when the mother was a twin than when the mother was a singleton, when controlling for non-standardised maternal birthweight. When adjusting for relative maternal birthweight ( z -score), the association between maternal plurality and offspring birthweight was not statistically significant. The results suggest that being born as a twin has no substantial consequences on offspring growth in utero and show that mean differences in birthweight between twins and singletons should be standardised when both groups are included in multivariate studies.     

Fetal programming: the perspective of single and twin pregnancies

Multiple pregnancy is associated with increased risk of adverse consequences for both mother and fetus(es), including increased rates of maternal hypertension and pre-eclampsia, spontaneous abortion, Caesarean delivery, low birthweight, birth prematurity, perinatal mortality, admission to neonatal intensive care and extended length of care, respiratory distress, cerebral palsy, developmental delay, contact with disability services and mortality to age 5 years. Premature birth, which affects 97% of triplets and 53.3% of twins in Australia, is not the sole factor involved. The rate of multiple pregnancy in Australia is 1.7%. This compares to 22.1% for pregnancies resulting from assisted reproduction technology (ART). As a result, 21.8% of babies born from ART are from a multiple pregnancy, in comparison to the USA where the majority of babies born from ART are from a multiple pregnancy. Additionally, the population rate of multiple births is rising due to the more frequent use of ART and continued multi-embryo transfers, which is operating against a background of rising implantation rates within ART clinics. Twins have been of interest from a programming perspective. However, analysis of associations between crude birthweight and subsequent metabolic risk factors or mortality in adulthood from chronic disease indicate that adaptations in pregnancy to support multi-fetal growth are not identical to fetal growth restriction in singleton pregnancies. Indeed, the process of 'maternal constraint' is incompletely understood and confounds such comparisons. From a programming perspective, it is a challenge to identify in twin pregnancies the transition from physiological adaptation to pathological growth restriction. Growth disparity between twins has been more illuminating of subtle adverse effects for the smaller of twin pairs in both blood pressure and insulin resistance in adulthood. Interestingly, these effects can be observed in both dizygotic and to a lesser degree in monozygotic twins, which indicates a role for both genetic and environmental factors in these measures. This suggests that, consistent with experimental studies in other species, the relationship between impaired growth in utero and chronic disease in later life is not simply mediated by a common genetic pathway.     

Maternal birthweight and outcome of twin pregnancy

There is evidence from singletons that maternal birthweight is positively related to offspring gestational length and birthweight, and some evidence of an inverse relationship with preterm birth. Among twins very preterm birth is the major cause of neonatal mortality and of immediate and later morbidity, including neurodevelopmental impairment. We hypothesised that the relationship between maternal birthweight and gestational length would be more evident in twin than in singleton pregnancies, as there is more variation in gestation in the former. Among 131 singleton mothers carrying twins, there was weak evidence of a positive relationship between maternal birthweight and twin gestational length (+0.6 weeks [95% CI -0.05, +1.3] per kg increase in maternal birthweight, but stronger evidence among 56 of these who went into labour spontaneously (+1.9 weeks [+0.7, +3.1], P = 0.003 for interaction). In the latter group we estimated that the odds of very preterm birth (at <32 weeks) were reduced by 50% [95% CI 10%, 82%] per 250 g increase in maternal birthweight. In the whole cohort, and in this subgroup, maternal birthweight was strongly positively related to both twin offspring total birthweight and total placental weight. Our data, consistent with intergenerational programming of early development, suggest the possibility of a stronger and more clinically relevant association among twins than among singletons. Nevertheless, our sample size was modest and this finding needs to be confirmed in a larger cohort.     

活产双胎低出生体重儿影响因素分析

目的探讨活产双胎低出生体重与相关因素关系。方法将657对活产双胎按出生体重分为体重均低组、单低体重组和体重正常组,配对分析双胎性别、出生次序与低出生体重的关系;分析母亲因素（孕龄、孕周、孕次、产次、血压、血红蛋白等）与出生体重的关系。结果双胎中第2个出生胎儿为低体重者明显多于第1个出生胎儿,女婴显著多于男婴。各体重组母亲孕周、产次比较差异有统计学意义;低体重组母亲孕初舒张压显著低于正常组,血红蛋白值始终高于体重正常组。结论双胎低出生体重与胎儿性别、出生顺序、母亲孕周、产次有关。双胎母亲孕期血压、血红蛋白与胎儿低出生体重间的关系是否属于对双胎妊娠的一种适应,有待进一步探讨。     

The cost of prematurity: a case-control study of twins vs singletons.

OBJECTIVES: This study evaluated the extent to which morbidity and costs at birth were associated with plurality, gestational age, and birth-weight with a sample of twins from a large urban hospital. METHODS: Each twin infant was matched to two singleton infants (control [ctrl]-singletons) for payor status and race, and to one singleton infant (gestation [ga]-singleton) for payor status, race, and gestational age; after exclusion of infants who were transferred, the study population included 111 twins, 242 ctrl-singletons, and 106 ga-singletons. Data were stratified by five gestational categories and compared across study groups. Outcomes included birthweight, neonatal diagnoses, infant length of stay, infant costs per day, and total infant and total birth costs. RESULTS: Total birth costs ranged from $280,146 at 25 to 27 weeks to $9,803 at 39 to 42 weeks, decreasing with advancing gestation to means of $88,891 (twins), $43,041 (ga-singletons), and $9,326 (ctrl-singletons). Twins did not differ from either group of singletons in prematurity-related diagnoses, length of stay, or costs until after 34 weeks' gestation. CONCLUSIONS: In this sample, prematurity, not plurality, was the predominant cost factor at birth. Compared with singletons, twins experienced increased morbidity and associated costs after 38 weeks' gestation.     

Maternal mental health and childrearing context in the development of children at 6, 18 and 36 months: a Taiwan birth cohort pilot study

Background This study investigated a possible pathway of the childrearing context and maternal mental health at 6 months, and how these factors influence children's development at 6, 18 and 36 months. Methods Using random sampling, 2048 children and mothers were selected. The mother's health status was evaluated using the Taiwanese version of the 36‐Item Short Form Health Survey (SF‐36), and infant development was assessed using the high reliable Taiwan birth cohort study instrument. All data were collected using parental self‐report, and were analysed using multiple linear regression analysis and further pathway using structural equation modelling. Results This study showed that 12 factors effected children's development at 6 months, and some dissipated with growth. Of these, maternal education had an enduring effect on different domains of child development, and this effect intensified as the child grew older. Children who grew up in a family with more siblings would show a delay in language development at 6 months; they have a delay in motor and social development at 18 and 36 months. Additionally, maternal mental health effected the children's fine motor development at 6 months. However, this effect disappeared at 18 months, and influenced children's social development at 36 months. Conclusions This study demonstrated that the development of children at as young as 6 months is affected by various factors. These factors may dissipate, continue to influence child development up to 3 years of age, turn from being disadvantageous to beneficial, or affect different domains of child development. Also, parental self‐report instrument might be has its limitation and could be contributed by several confounding factors. Thus, continuous longitudinal follow‐up on changes in maternal conditions, family factors, and environmental factors is vital to understand how these early infantile factors affect each other and influence the developmental trajectories of children into early childhood.     

Trends in twin and triplet births: 1980-97.

This report presents data from U.S. birth certificates on the numbers and rates of twin and triplet and other higher order multiple births for 1980-97. Over the study period, the number of twin births rose 52 percent (from 68,339 to 104,137) and triplet and other higher order multiple births (heretofore referred to as "triplet/+") climbed 404 percent (from 1,337 to 6,737 births). Comparable but less pronounced rises were observed in twin and triplet/+ birth rates. Growth in twin and triplet/+ birth rates was most marked among women aged 30 years and over. Between 1980-82 and 1995-97, the twin rate rose 63 percent for women aged 40-44 years, and soared nearly 1,000 percent for women 45-49 years. (As one result, there were more twins born to women 45-49 years of age in 1997, than during the entire decade of the 1980's.) The triplet/+ birth rate rose nearly 400 percent for women in their thirties and exploded by more than 1,000 percent for women in their forties. The extraordinary rise in multiple births resulted in a shift in age-specific patterns, and the highest twin and triplet/+ birth rates now are for women 45-49 years of age. Historical differences in twinning rates between non-Hispanic white and black mothers have been largely eliminated (28.8 per 1,000 non-Hispanic white compared with 30.0 for black women). Non-Hispanic white women were more than twice as likely as non-Hispanic black or Hispanic women to have a triplet/+ birth. Rates of low birthweight, very low birthweight, and infant mortality were 4 to 33 times higher for twins and triplet/+ compared with singleton births. The risk for these adverse outcomes was lowest for twins and triplet/+ born to women 35-44 years of age. Twin birth rates for Massachusetts and Connecticut were at least 25 percent higher than the U.S. rate; triplet/+ rates for Nebraska and New Jersey were twice the national level.     

Birth Weight Effects on Children’s Mental, Motor, and Physical Development: Evidence from Twins Data

Objective To determine the effect of very low birth weight (VLBW; <1500 g) and moderately low birth weight (MLBW; 1500–2499 g) on children’s mental and motor development and physical growth during the first 2 years of life and whether VLBW and MLBW babies catch up to normal birth weight (NBW; ≥2500 g) children by age 2. Methods We use data on dizygotic (DZ) and monozygotic (MZ) twins and singleton births from the first two waves of the Early Childhood Longitudinal Study—Birth Cohort (ECLS-B), a nationally representative dataset of children born in the US in 2001. We estimate the effects of VLBW and MLBW on children’s mental and motor development scores, weight-for-age, weight-for-length, weight-for-height, and length-for-age z-scores at 9 months and 2 years. We examine whether differences in outcomes within twin pairs are related to differences in their birth weights. The within-twins analysis is conducted on samples of DZ and MZ twins. For comparison, we also estimate birth weight effects on child outcomes from multivariate linear regression models using the full singleton and twins’ sample. We also estimate the effect of being small-for-gestational age (SGA; birth weight <10th percentile for gestation) using the same set of models in order to separate out the effects of fetal growth restriction from prematurity. Results Evaluation of all births showed that VLBW and MLBW have large negative effects on mental development, motor development, and growth at 9 months and 2 years of age. However, results from within-twin models with DZ twins that control for shared maternal and environmental factors showed much less effect of birth weight on mental or motor development, but continued large effects on growth for the VLBW group. Within-twin models with MZ twins that control for shared maternal, environmental, and genetic factors showed statistically insignificant effects of birth weight on mental and motor development, but continued effects on growth. Similar patterns were found when examining the effects of SGA. Conclusions After controlling for the influence of maternal, environmental, and genetic factors, low birth weight has at most a small negative effect on children’s mental and motor development in their first 2 years of life. However, low birth weight is a major risk factor for children’s physical growth in the early years and there is no evidence of catch-up by age 2.     

The epidemiology of perinatal mortality in multiple births.

The epidemiology of perinatal mortality in multiple pregnancies was investigated from data on 16,831 multiple births from New York City''s computerized vital records for 1978-1984. Twins had a sixfold higher rate of neonatal death and a threefold higher rate of fetal death during labor than had singleton infants. Much of this excess mortality can be explained by the lower birthweight distribution in twins: between 1,001 and 2,500 grams twins had birthweight-specific death rates equivalent to or substantially less than singletons. However, in infants of normal birthweights, twins had more than three times the mortality risk of singletons. For twins in vertex presentation between 1,001 and 3,000 grams, cesarean section did not appreciably reduce neonatal mortality risk. For twins in vertex presentation who weighted more than 3,000 grams the neonatal mortality rate was more than four times higher in vaginal deliveries than in cesarean sections (exact p = 0.034). Efforts to prevent intrapartum and neonatal mortality in multiple births should aim at reducing the incidence of low birthweight twins. More research is needed on the etiology of perinatal problems in normal birthweight twins (greater than or equal to 2,501 grams), especially on the effects of different modes of delivery.     

The influence of maternal age on very preterm birth of twins: differential effects by parity

For singleton births, parity can modify the effect of maternal age on birth outcomes such as low birthweight and preterm birth; however, it is unknown whether this relationship exists for twin births. As the rate of twin births increases among older women, it is important to understand how parity may influence the relationship between maternal age and adverse birth outcomes. The NCHS Matched Multiple Birth Data Set, which contains all twin births in the USA from 1995 to 1998, was analysed. Parity was grouped into two levels (primiparous--no prior live births, and multiparous--at least one prior live birth), and maternal age was divided into the following groups: 20-24, 25-29, 30-34, 35-39, and 40 years or more. Very preterm birth was defined as births occurring before 33 weeks. Logistic regression was used to obtain odds ratios (OR) to estimate the risk of very preterm birth, and to determine the relationships between parity, maternal age, and very preterm birth. Among primiparae, women 40 years and older had a reduced risk of very preterm birth compared with women of 25-29 years (OR 0.74 [95% CI=0.66, 0.84]). Among multiparae, women 40 years and older had the same risk of very preterm birth compared with women of 25-29 years (OR 1.00 [95% CI=0.90, 1.12]). However, stratification by education revealed that the age gradient was limited to women with >12 years education among primiparae. The effect of maternal age on very preterm birth of twins differs according to parity. To some extent, that effect is further modified by education. Therefore, future analyses of maternal age and twin birth outcomes should account for measures of obstetric history and other factors, which may influence these results.     

Fetal growth and neonatal mortality in Korea

The fetal growth curve and neonatal mortality rate, based on gestational age and birthweight, are important for identifying groups of high-risk neonates and developing appropriate medical services and health-care programmes. The purpose of this study was to develop a national fetal growth curve for neonates in Korea, and examine the Korean national references for fetal growth and death according to their characteristics. Data of Korean vital statistics linked National Infant Mortality Survey conducted on births in 1999 were used in this study. The total livebirths were 621,764 in 1999, which were grouped into singletons (n = 609,643) and twins (n = 9805) for analysis. Birthweight/gestational age-specific fetal growth curves and neonatal mortality rates were based on 250 g of birthweight and weekly gestational age intervals for each characteristic of the birth. The features of high-risk neonates such as small-for-gestational-age and the limit of viability in Korea were different from those of Western countries. Difference in fetal growth and death was also detected in other characteristics of the fetus (gender and plurality of birth) besides race. The fetal growth curve of males was higher than that of females, and was higher in singleton than in twins. The neonatal mortality rate was higher in males (singleton, 2.6; twin, 23.5) than females (singleton, 2.1; twin, 15.9), and higher in twins (19.8/1000) than in singletons (2.4/1000). However, in neonates with gestational age >29 weeks and birthweight >1000 g, the neonatal mortality rate was lower in twins than in singletons. The limit of viability was gestational age 27 weeks and birthweight 1000 g, which was similar in singletons and twins regardless of gender. To improve the health of neonates in a country, it is imperative to investigate the characteristics of fetal growth and death under the particular circumstances of the country. When risk is defined for neonates account must be taken of differences in race, gender and plurality of birth, as the neonatal mortality rate varies depending on those factors.     

Infant mortality rates in single, twin and triplet births, and influencing factors in Japan, 1995–98

The infant mortality rate (IMR) was analysed among single, twin and triplet births during the period from 1995 to 1998 using Japanese Vital Statistics. This study also investigated the effects of order of multiple births and of birthweight on the IMR. Proportions of neonatal deaths among total infant deaths were about 1/2 for singletons and 3/4 for both twins and triplets. Thus, to reduce the IMR, intensive care of multiple births is likely to be very important during the first month of life. The IMR was higher in males than females for both singletons and twins, but not in triplets. Relative risks of the IMR in multiples relative to singletons were 5-fold in twins and 12-fold in triplets. The IMR was higher in the second-born (18 per 1000 live births) than the first-born (16) twin and higher in the third-born (51) than the first-born (31) and the second-born (34) triplet. The higher risk in the second-born than the first-born twin may be related to delivery complications. The IMR decreased rapidly as birthweight increased in singletons, twins, and triplets. IMRs for < or =1500 g were 2.4 per 1000 live births in singletons, 5.9 in twins and 6.1 in triplets. The corresponding proportions of infant deaths were 75%, 33% and 10% respectively. The higher relative risks of multiple births are almost entirely the result of the lower birthweight distribution among twins and triplets. To reduce the IMR, birthweight is an important factor in twins, triplets and singletons. The overall early neonatal death rate decreased as gestational age rose in singletons, twins and triplets. For birthweights <1000 g, higher IMRs were related to gestational ages of <28 weeks.     

Maternal stress and young children's behavioural development: a prospective pilot study from 8 to 36 months in a Finnish sample

The relationship between maternal parenting stress and infant/toddler behavioural development was examined in a longitudinal pilot study. Fifty mothers reported parenting stress via the Parenting Stress Index – Short Form when their infants were eight months old. Parents subsequently rated their children's emotional and behavioural problems with the Child Behaviour Checklist at both 18 and 36 months of age. Preliminary results suggest that mothers reporting higher stress levels in their infant's first eight months also reported greater emotional and behavioural problems in their children at 18-and 36-month follow-up assessment. Parent report of children's total and externalising problematic behaviours decreased over time, regardless of the maternal stress level. In contrast, parent report of internalising problem behaviours remained stable over time; however, at both 18-and 36-month follow-up assessments, high-stress mothers reported higher levels of internalising problems in their children than did low-stress mothers.     

Congenital malformations in twins in England and Wales.

STUDY OBJECTIVE--The aim was to compare congenital malformation rates in twin births with those in singleton births. DESIGN--The study was an analysis of malformation rates in singleton and twin births using data from the Office of Population Censuses and Survey's Congenital Malformation Notification Scheme. SETTING--This was a national survey of births in England and Wales in 1979-1980 and 1982-1985. PARTICIPANTS--The data comprised 95,510 reported malformations in 3.7 million singleton births, and 1925 reported malformations in 76,000 twin births. MEASUREMENTS AND MAIN RESULTS--Twin malformation ratios were calculated using maternal age specific singleton rates as standard. In comparison with singleton births, twins have significantly higher reported frequencies of indeterminate sex and pseudohermaphroditism; anencephaly; patent ductus arteriosis; exomphalos; hydrocephalus; anomalies of the umbilical vessels; atresia or stenosis of the large intestine or anus; and tracheo-oesophageal fistula, atresia or stenosis. Twins also have significant reported deficits of polydactyly and syndactyly; congenital dislocation of the hip; anomalies of the tongue, branchial cleft and auricular sinus; post-anal dimple; and Down's syndrome. CONCLUSIONS--Several major malformations were significantly more common in twins than in singletons. The excess of indeterminate sex and pseudohermaphroditism has not been described before and may be analogous to freemartinism in cattle. Most of the conditions less common in twins are minor, and the reported deficits may be due to underascertainment of the less serious conditions in twins. Down's syndrome is an exception, and the deficit may well be real.     

Reference birthweight for multiple births in Japan

PURPOSE: Intrauterine growth curves of twins, that is, birth weights according to gestational age, were calculated from birth certificate data. METHODS: Multiple births were identified by birthplace, ages of the parents, gestational age, and year and month of birth. There were 49,240 twin births in Japan between 1988 and 1991. Of these, 32,232 livebirth-livebirth pairs, 679 livebirth-stillbirth pairs, and 278 stillbirth-livebirth pairs were included in this analysis. There were also 1894 triplet live births from 744 sets of triplets and 206 quadruplet live births analyzed. For all, access was made to the database of birth certificates in the form of magnetic tapes giving birthweights in hundred gram categories. RESULTS: For all gestational ages, median birthweights of males were ca. 0.05 kg-0.1 kg larger than female values. Compared to singleton births in Japan, median birthweights of twins remained ca. 0.15 kg smaller until gestational age of 34 weeks, the difference then increasing to ca. 0.5 kg at 42 weeks of gestation. As for birth order, mean birthweight of the first twin was larger than that of the second and the standard deviation was larger for the second. Birthweights of twins from multiparous mothers were greater than those from primiparous mothers. Among the multiple births, median birthweight for gestational age was found to be greatest in twins, lower in triplets and lowest in quadruplets. In triplets, the 50th centile for boys was 0.08 kg larger than for girls. DISCUSSION: With regard to perinatal growth, the fetus is affected more or less by the limitation of uterine expansion in the late gestational weeks. Reference birthweights for exclusive use for multiple births are different from that for singletons.     

The recognition and significance of the vanishing twin

With the advent of sonography, a twin pregnancy may be diagnosed in early gestation. Serial sonographic examinations can show the disappearance of one of two twins. We offer evidence of an early twin pregnancy with a "vanishing twin," resulting in a liveborn singleton plus a fetus papyraceus. There is an increasing body of information about explanations, management, and complications associated with a multiple gestation and fetal death. The distinction between monochorionic and dichorionic twins is important in their management and for both maternal and fetal prognosis. Identification of dizygotic twins through chromosomal or sonographic studies, revealing separate placentas, separate membranes, or different sexes, theoretically allows the physician to predict a favorable outcome for the live twin and the mother.     

Expressive vocabulary in 18-month-old children in relation to demographic factors, mother and child characteristics, communication style and shared reading

Background Previous research has elucidated the associations between children's language development and reading habits, and maternal education, communication style, gender and birth order. Research including maternal age and child temperament is more scarce. We studied the associations of all these factors with children's expressive vocabulary and reading habits. We also analysed the relationships of reading with expressive vocabulary, and effect sizes associated with frequent reading. Methods Questionnaires were completed by mothers of 1091 children aged 17–19 months visiting the Swedish Child Health Services. Expressive vocabulary was assessed by the Swedish Communication Screening at 18 months, a screening version of McArthur‐Bates Communicative Development Inventories. Mother's perception of ability to communicate was measured by a scale constructed ad hoc from the International Child Development Programmes, a parent education curriculum. Bates' ‘difficultness’ scale was used to assess temperament. Results Good communication, low maternal age, female gender and frequent reading were significantly associated with expressive vocabulary. High maternal education, good communication, higher maternal age, female gender and being a first‐born child were significantly associated with frequent reading. Reading at least 6 times/week added more than 0.3 SD in vocabulary regardless of gender and communication. Conclusions The findings support the importance of reading and communication quality to early language development. Knowledge of the relationship between children's vocabulary and book reading in a context of joint attention is both theoretically and practically valuable to speech and language pathologists, pre‐school teachers, child health workers and other professionals.     

Maternal general health and children's cognitive development and behaviour in the early years: findings from the Millennium Cohort Study

Background Mothers often experience physical and psychological difficulties during the post‐natal period and these may continue through the early years of raising children and have negative effects on engagement and caregiving. Pathways between maternal depression, parental engagement and caregiving and children's subsequent development have been described in longitudinal studies; yet, less is known about how other aspects of maternal health may influence children's development. Methods A longitudinal analysis within the Millennium Cohort Study was conducted including 7906 families from England. Maternal general health and psychological well‐being were assessed when their children were 9 months and 3 years old, socio‐demographic characteristics were assessed at 9 months, and engagement and caregiving were assessed at 3 years. These were examined as predictors of children's learning and development and behaviour at age 5. Results There are clear associations between maternal general health and children's development with regard to both learning and development and behaviour. These effects are reduced if psychological distress is taken into account; yet, maternal general health maintains importance as a predictor for children's subsequent development. There is evidence of an association via engagement and caregiving which links maternal health to children's development and evidence of the influence of underlying socio‐demographic disadvantage. Conclusion General maternal health as well as psychological well‐being during the early years of raising children may be influential for children's development. This study suggests the need for a broader recognition of maternal health as well as psychological well‐being as a foundation for family well‐being, and speaks to support for mothers in maintaining engagement and caregiving for their children during periods of ill health.     

Twinship as a protective factor against behavioural and emotional problems at preschool age

Early attachment has both protective and risk factors as regards later mental health. In Finland, insecure-avoidant-type attachment is overrepresented. Does this indicate a risk for emotional and behavioural problems at preschool age? In this study, we examined and compared the association between attachment and mental health in Finnish singletons and twins. The attachment of 27 singletons and 58 twins with both parents had previously been examined at the age of 18 months using Preschool Assessment of Attachment criteria. At the age of 4, the children's emotional and behavioural symptoms were assessed using Child Behavior Checklist questionnaires reported by parents. The mothers and fathers reported significantly more behavioural and emotional problems at preschool age in singletons than in twins. Insecure-avoidant-type attachment to the mother was significantly associated with higher scores concerning withdrawal, somatic problems and total internalising symptoms among singleton preschoolers, whereas among twins, no such correlations were observed. The results thus suggest that twinship is a protective factor in the trajectory from toddler avoidant attachment to internalising problems at preschool age.     

Assisted reproductive technologies and birth outcomes: overview of recent systematic reviews

Several systematic reviews have been published recently on birth outcomes of infants conceived through assisted reproductive technologies (ART), compared with infants conceived spontaneously. These outcomes include perinatal mortality, preterm birth, low birthweight and birth defects. Methodological limitations of many of the individual studies (including small sample size, potential for bias in ascertainment of outcomes and considering singletons and multiples together) were obviated in these reviews by excluding studies where methods were considered inadequate, by conducting meta-analyses using data from all methodologically sound studies (small and large) and by examining singletons separately. Overall, the reviews indicate few differences between outcomes in ART twins compared with twins conceived spontaneously. However, in singleton ART infants, there are around two-fold increases in risk of perinatal mortality, low birthweight and preterm birth, about a 50% increase in small for gestational age and a 30-35% increase in birth defects, compared with singletons conceived spontaneously. Couples considering ART should be counselled about the increased risk of adverse outcomes. Epidemiologists, in conjunction with clinical and laboratory colleagues, should now focus on large, methodologically sound studies with long-term follow up that seek to identify the reasons for these increased risks and their long-term consequences, whether they are associated with particular technologies and causes of infertility, and how they might be reduced.