Is there a consequence for fetal growth of having an unlike-sexed cohabitant in utero?

Pituitary gland height evaluated with magnetic resonance imaging in premature twins: the impact of growth and sex

BACKGROUND

Pituitary gland height reflects secretory activity of the hypothalamo-pituitary axis.

OBJECTIVE

To assess the cumulative impact of fetal growth and sex on pituitary gland height in premature twins, dissociated from prematurity.

MATERIALS AND METHODS

A retrospective study was conducted, assessing the pituitary gland height in 63 pairs of preterm twins, measured from T1-weighted magnetic resonance imaging (MRI). Auxological parameters, including body weight, body length, and head circumference, at birth and at the time of MRI, were used as proxies for fetal and postnatal growth, respectively. The study population was divided into two groups, using corrected age at around term equivalent as the cutoff point. Statistical analysis was performed using mixed-effects linear regression models.

RESULTS

When pituitary gland height was evaluated at around term equivalent, a greater pituitary gland height, suggesting a more immature hypothamo-pituitary axis, was associated with the twin exhibiting lower auxological data at birth. The same association was observed when body weight and length at MRI were used as covariants. In the group evaluated after term equivalent, a smaller pituitary gland height, suggesting a more mature hypothamo-pituitary axis, was associated with male sex. This difference was observed in twin pairs with higher average body weight at birth, and in babies exhibiting higher auxological data at MRI.

CONCLUSION

After isolating the effect of prematurity, at around term equivalent, pituitary gland height reflects the cumulative impact of fetal growth on the hypothalamo-pituitary axis. Subsequently, pituitary gland height shows effects of sex and of fetal and postnatal growth.

Sibling rivalry between twins in utero and childhood: Evidence from birthweight and survival of 95 919 twin pairs in 72 low- and middle-income countries

BACKGROUND

This study explores the magnitude and timing of sex and gender disparities in child development by describing differences in health outcomes for male and female siblings, comparing twins to control for all aspects of life circumstances other than sex and gender.

METHODS

We construct a repeat cross-sectional dataset of 191 838 twins among 1.7 million births recorded in 214 nationally representative household surveys for 72 countries between 1990 and 2016. To test for biological or social mechanisms that might favor the health of male or female infants, we describe differences in birthweights, attained heights, weights, and survival to distinguish gestational health from care practices after each child is born.

RESULTS

We find that male fetuses grow at the expense of their co-twin, significantly reducing their sibling's birthweight and survival probabilities, but only if the other fetus is male. Female fetuses are born significantly heavier when they share the uterus with a male co-twin and have no significant difference in survival probability whether they happen to draw a male or a female co-twin. These findings demonstrate that sex-specific sibling rivalry and male frailty begin in utero, prior to gender bias after birth that typically favors male children.

CONCLUSIONS

Sex differences in child health may have competing effects with gender bias that occurs during childhood. Worse health outcomes for males with a male co-twin could be linked to hormone levels or male frailty, and could lead to underestimates of the effect sizes of later gender bias against girls. Gender bias favoring surviving male children may explain the lack of differences in height and weight observed for twins with either male or female co-twins.

The association of sex of co-twin and birth size in twins born in Yucatan, Mexico between 2008 and 2017

Background: Birth measures of twins are potentially influenced by sex of co-twin.Aim: To analyse the association between sex of co-twin and birth weight, length and ponderal index in twin infants from Yucatan, Mexico.Subjects and methods: A total of 2057 twin pairs born during 2008-2017 were analysed. Female-female (F-F), male-male (M-M) and male-female (M-F) twin pair types were defined. Multiple linear regression models were used to analyse the association of (1) being female from M-F pairs and birth measures among overall female infants (M-F and F-F), and (2) being male from M-F pairs and birth measures among overall male infants (M-F and M-M). The length of gestation and mothers' age and level of education were used as covariates.Results: Models showed that being male from M-F pairs was associated with increases of 81 g in birth weight and 0.61 cm in length, compared to males from M-M pairs, and being female from opposite-sex pairs was associated with increases of 0.36 cm in length, compared to females from same-sex pairs.Conclusions: Males from M-F pairs show greater birth size than males from same-sex pairs, which supports the hypothesis that birth measures of twins are influenced by sex of the co-twin.

Birth size and gestational age in opposite-sex twins as compared to same-sex twins: An individual-based pooled analysis of 21 cohorts

It is well established that boys are born heavier and longer than girls, but it remains unclear whether birth size in twins is affected by the sex of their co-twin. We conducted an individual-based pooled analysis of 21 twin cohorts in 15 countries derived from the COllaborative project of Development of Anthropometrical measures in Twins (CODATwins), including 67,850 dizygotic twin individuals. Linear regression analyses showed that boys having a co-twin sister were, on average, 31 g (95% CI 18 to 45) heavier and 0.16 cm (95% CI 0.045 to 0.274) longer than those with a co-twin brother. In girls, birth size was not associated (5 g birth weight; 95% CI −8 to −18 and −0.089 cm birth length; 95% CI −0.202 to 0.025) with the sex of the co-twin. Gestational age was slightly shorter in boy-boy pairs than in boy-girl and girl-girl pairs. When birth size was standardized by gestational age, the magnitude of the associations was attenuated in boys, particularly for birth weight. In conclusion, boys with a co-twin sister are heavier and longer at birth than those with a co-twin brother. However, these differences are modest and partly explained by a longer gestation in the presence of a co-twin sister.

Does the sex of one's co-twin affect height and BMI in adulthood? A study of dizygotic adult twins from 31 cohorts

Background

The comparison of traits in twins from opposite-sex (OS) and same-sex (SS) dizygotic twin pairs is considered a proxy measure of prenatal hormone exposure. To examine possible prenatal hormonal influences on anthropometric traits, we compared mean height, body mass index (BMI), and the prevalence of being overweight or obese between men and women from OS and SS dizygotic twin pairs.

Methods

The data were derived from the COllaborative project of Development of Anthropometrical measures in Twins (CODATwins) database, and included 68,494 SS and 53,808 OS dizygotic twin individuals above the age of 20 years from 31 twin cohorts representing 19 countries. Zygosity was determined by questionnaires or DNA genotyping depending on the study. Multiple regression and logistic regression models adjusted for cohort, age, and birth year with the twin type as a predictor were carried out to compare height and BMI in twins from OS pairs with those from SS pairs and to calculate the adjusted odds ratios and 95% confidence intervals for being overweight or obese.

Results

OS females were, on average, 0.31 cm (95% confidence interval (CI) 0.20, 0.41) taller than SS females. OS males were also, on average, taller than SS males, but this difference was only 0.14 cm (95% CI 0.02, 0.27). Mean BMI and the prevalence of overweight or obesity did not differ between males and females from SS and OS twin pairs. The statistically significant differences between OS and SS twins for height were small and appeared to reflect our large sample size rather than meaningful differences of public health relevance.

Conclusions

We found no evidence to support the hypothesis that prenatal hormonal exposure or postnatal socialization (i.e., having grown up with a twin of the opposite sex) has a major impact on height and BMI in adulthood.

Electronic supplementary material

The online version of this article (doi:10.1186/s13293-017-0134-x) contains supplementary material, which is available to authorized users.

The Impact of Gender on Anthropometric Measures of Twins

INTRODUCTION

Literature suggests that male hormones influence fetal growth in singleton pregnancies. We hypothesized that the same phenomenon is seen in twin gestations.

OBJECTIVES

(1) to identify the impact of gender associated with fetal birth weight, head circumference, and birth length for twins; (2) to examine the effect of gender on standardized fetal growth at birth, according to gestational age and birth order; (3) to examine the effect of gender on placenta weight and dimensions.

METHODOLOGY

This was a population-based retrospective cohort study of twins (4,368 twins, 2,184 pairs) born in British Columbia, Canada from 2000-2010. We excluded twins with stillbirth, congenital anomalies, and those delivered with cesarean section. We also controlled for confounding factors, including birth order, gestational age, maternal anthropometric measures, maternal smoking habits, and obstetric history. A subsample of this population was analyzed from Children and Women Hospital to obtain chorionicity information.

RESULTS

Male-male twins were heavier than male-females and female-female twin pairs (p=.01). Within sex-discordant twin pairs, males were also heavier than females (p=.01). Regression analysis suggested that gender affects birth weight independent of birth order and gestational age. Other newborn anthropometric measures were not found to be dependent on gender. In analyzing a subsample with chorionicity data, birth weight was the only anthropometric measure that was both statistically and clinically affected by sex, even after adjustment for gestational age, chorionicity, birth order, and maternal age.

CONCLUSION

Birth weight was affected by gender while head circumference and birth length were not.

Academic performance of opposite-sex and same-sex twins in adolescence: A Danish national cohort study

Testosterone is an important hormone in the sexual differentiation of the brain, contributing to differences in cognitive abilities between males and females. For instance, studies in clinical populations such as females with congenital adrenal hyperplasia (CAH) who are exposed to high levels of androgens in utero support arguments for prenatal testosterone effects on characteristics such as visuospatial cognition and behaviour. The comparison of opposite-sex (OS) and same-sex (SS) twin pairs can be used to help establish the role of prenatal testosterone. However, although some twin studies confirm a masculinizing effect of a male co-twin regarding for instance perception and cognition it remains unclear whether intra-uterine hormone transfer exists in humans. Our aim was to test the potential influences of testosterone on academic performance in OS twins. We compared ninth-grade test scores and teacher ratings of OS (n=1812) and SS (n=4054) twins as well as of twins and singletons (n=13,900) in mathematics, physics/chemistry, Danish, and English. We found that males had significantly higher test scores in mathematics than females (.06-.15 SD), whereas females performed better in Danish (.33-.49 SD), English (.20 SD), and neatness (.45-.64 SD). However, we did not find that OS females performed better in mathematics than SS and singleton females, nor did they perform worse either in Danish or English. Scores for OS and SS males were similar in all topics. In conclusion, this study did not provide evidence for a masculinization of female twins with male co-twins with regard to academic performance in adolescence.

ADHD and overweight in boys: cross-sectional study with birth weight as a controlled factor

Population studies indicate a strong relationship between birth weight (BW) and body size in later life. However, BW as a variable was never accounted for in studies on the relationship between attention-deficit/hyperactivity disorder (ADHD) and overweight. This study aims to assess the relationship between ADHD and overweight with control of birth weight and other confounding factors. Prevalence of overweight was compared in clinical sample of 219 boys with ADHD and 396 boys without ADHD, aged 6-18 years. The following factors were controlled: BW, parents income and education level, place of residence, ADHD type, selected comorbid disorders and stimulant treatment. Overweight and obesity were diagnosed according to the criteria proposed by the International Obesity Task Force. Logistic regression analysis was used to estimate the association between ADHD and the prevalence of overweight and obesity. Boys with ADHD differed significantly from the control group in distribution of low BW (8.2 vs. 3.0 %, χ (2) = 8.23, p = 0.02). Low BW was associated with a lower prevalence of overweight than normal and high BW (0 vs. 12.14 %, χ (2) = 4.12, p = 0.04). Overweight was observed significantly more often in boys with ADHD (17.3 vs. 8.3 %, χ (2) = 11.23, p < 0.001) even after adjustment for BW and other variables (OR = 2.44, 95 % CI 1.38-4.29, p = 0.002) and after controlling for ADHD type, stimulant treatment and selected comorbid disorders. Independently to applied analysis, obesity was not associated with ADHD. Lower birth weight is over twice more often observed in boys with ADHD than in control group. Although this phenomenon may reduce the rate of overweight in the studied group, ADHD remains strongly associated with increased prevalence of overweight.

Impact of sex on perinatal mortality and morbidity in twins

OBJECTIVE

Twin studies offer opportunities to investigate mechanisms underlying sex-associated differences in perinatal outcomes. The objective of the study was to investigate sex-related differences in perinatal complications.

STUDY DESIGN

A cohort of 16,045 twin pregnancies - 32,090 twins - was explored for obstetric complications, perinatal and infant mortality, and neonatal morbidities.

RESULTS

Twin pregnancies with a female fetus had an increased risk for preeclampsia, but otherwise there were no pregnancy complications associated with fetal sex. After birth, female-female twins had lower early neonatal and infant mortality, and lower risk for respiratory morbidities than male-male twins at all gestational ages. In unlike-sexed twin pairs, very preterm males had higher respiratory morbidity than females and, females were at higher risk for being growth restricted.

CONCLUSION

Male-male twins have higher respiratory morbidity and neonatal mortality than female-female twins. In unliked-sexed twin pairs, the males seem to be protected by having a female co-twin.

Hormones and endocrine-disrupting chemicals: low-dose effects and nonmonotonic dose responses

For decades, studies of endocrine-disrupting chemicals (EDCs) have challenged traditional concepts in toxicology, in particular the dogma of "the dose makes the poison," because EDCs can have effects at low doses that are not predicted by effects at higher doses. Here, we review two major concepts in EDC studies: low dose and nonmonotonicity. Low-dose effects were defined by the National Toxicology Program as those that occur in the range of human exposures or effects observed at doses below those used for traditional toxicological studies. We review the mechanistic data for low-dose effects and use a weight-of-evidence approach to analyze five examples from the EDC literature. Additionally, we explore nonmonotonic dose-response curves, defined as a nonlinear relationship between dose and effect where the slope of the curve changes sign somewhere within the range of doses examined. We provide a detailed discussion of the mechanisms responsible for generating these phenomena, plus hundreds of examples from the cell culture, animal, and epidemiology literature. We illustrate that nonmonotonic responses and low-dose effects are remarkably common in studies of natural hormones and EDCs. Whether low doses of EDCs influence certain human disorders is no longer conjecture, because epidemiological studies show that environmental exposures to EDCs are associated with human diseases and disabilities. We conclude that when nonmonotonic dose-response curves occur, the effects of low doses cannot be predicted by the effects observed at high doses. Thus, fundamental changes in chemical testing and safety determination are needed to protect human health.

The Natural Course of Monochorionic and Dichorionic Twin Pregnancies: A Historical Cohort

Current early diagnosis, surveillance and intervention options make it hard to determine the natural course of twin pregnancies, especially regarding spontaneous preterm delivery and perinatal mortality. We studied the natural course in monochorionic (MC) and dichorionic (DC) twin pregnancies in a historical cohort. Twin pregnancies were studied in a unique database of 651 twin pairs born in the period 1907 to 1938. We examined the effect of chorionicity on gestational age, birthweight, peri-natal mortality, intertwin birthweight differences, the incidence of preeclampsia and maternal mortality. Perinatal mortality was 27.7% for MC and 15.8% for DC twins (p < .001). Gestational age and birthweight were stronger predictors of perinatal mortality than chorionicity. Perinatal outcome was poorer for the second twin, especially in DC twins. Delivery before 37 weeks of gestation occurred more often in MC twin pregnancies (48.8% compared to 33.3% in DC twin pregnancies). DC twins were on average 288 g (95% confidence interval 201–376) heavier than MC twins. Severe birthweight discordancy occurred equally in MC and DC twins (18.1%). However, if present, mortality was only increased in MC twins. The birthweight of girls was not affected by the presence of a male co-twin. In this historical cohort MC twin pregnancies had a higher perinatal mortality, caused by a high incidence of low birthweight mainly due to preterm delivery. Mortality did not differ in deliveries after 31 weeks of gestation, which is in contrast to recent data. Apparently, modern obstetrics is more effective in reducing mortality in DC twins.

Sexual orientation and the auditory system

The auditory system exhibits differences by sex and by sexual orientation, and the implication is that relevant auditory structures are altered during prenatal development, possibly by exposure to androgens. The otoacoustic emissions (OAEs) of newborn male infants are weaker than those of newborn females, and these sex differences persist through the lifespan. The OAEs of nonheterosexual females also are weaker than those of heterosexual females, suggesting an atypically strong exposure to androgens some time early in development. Auditory evoked potentials (AEPs) also exhibit sex differences beginning early in life. Some AEPs are different for heterosexual and nonheterosexual females, and other AEPs are different for heterosexual and nonheterosexual males. Research on non-humans treated with androgenic or anti-androgenic agents also suggests that OAEs are masculinized by prenatal exposure to androgens late in gestation. Collectively, the evidence suggests that prenatal androgens, acting globally or locally, affect both nonheterosexuality and the auditory system.

Differences in anthropometric measurements between Sudanese newborn twins and singletons

Twin pregnancies are associated with disturbed fetal growth and a higher risk of low birthweight (LBW), which is one of the most important determinants of perinatal morbidity and mortality in Africa. In this study, we compare anthropometric measurements in Sudanese twins and their mothers with singletons.

METHODS

In 1000 Sudanese mothers with singleton births and 30 mothers with twins, maternal (weight, height, mid-arm circumference) and 11 newborn anthropometric measurements were taken within 24 hours of delivery. Maternal education and socio-economic status were additionally recorded.

RESULTS

Mothers of twins had a significantly higher body weight (p = .045) and lean body mass (p = .02) after delivery, and were from higher social classes in general (p = .014). In addition to gestational age, twins displayed a statistically significant reduction in all anthropometric data, compared to singletons, mainly in terms of birth-weight, chest and head circumference, whereas differences in triceps and subscapular skin fold thickness and ponderal index were distinctly lower. The LBW rate in twins was markedly higher than that in singletons (43.3% vs. 8.3%, p < .001). In 20 out of 30 twins (66.7%), Twin A weighed more than Twin B (difference (SD) of 443 (335) g), and in the remaining 10 cases (33.7%), the weight of Twin B was equal to or more than that of twin A (difference (SD) of 211 (240) g, p = .039). In unlike-sex pairs, the mean (SD) difference between Twins A and B in birthweight was 459 (481) g, which was distinctly higher, compared to same-sex pairs (boys, 180 (325) g and girls, 36 (413) g).

CONCLUSIONS

Sudanese twins displayed significantly reduced anthropometric measurements compared to singletons, but to different degrees. Gender had a higher impact on birthweight in twins than in singletons.

Birth weight discordance in multiple gestations: Occurrence and outcomes

This paper reviews the patterns of occurrence, measurement and the effect of birth weight discordance on fetal and neonatal mortality in multiple pregnancies (twins and triplets). Birth weight discordance is fairly common among multiple pregnancies, and about one-quarter of the twin deliveries are affected by a birth weight discordance of 15%, while nearly 5% of twin gestations experience severe discordance (>or= 35%). Factors influencing birth weight discordance are exaggerated in triplet deliveries. Approximately 20% of triplet sets experience a birth weight discordance of 25 - 35% and nearly 10% experience severe forms of discordance. Frequencies of discordant sets at >25% discordance along the range of birth weight deciles show an inverse logarithmic relationship in twins, while the best-fit function in triplets is polynomial. Birth weight discordance is significantly associated with both fetal and neonatal mortality. Neonatal demise among the severely discordant smaller twin is significantly more frequent than in a non-discordant smaller twin. The magnitude of the effect is greater when one or both of the discordant twins are concomitantly small for gestational age.

Traces of embryogenesis are the same in monozygotic and dizygotic twins: not compatible with double ovulation

Common knowledge of over a century has it that monozygotic and dizygotic twinning events occur by unrelated mechanisms: monozygotic twinning 'splits' embryos, producing anomalously re-arranged embryogenic asymmetries; dizygotic twinning begins with independent ovulations yielding undisturbed parallel embryogeneses with no expectation of departures from singleton outcomes. The anomalies statistically associated with twin births are due to the re-arranged embryos of the monozygotics. Common knowledge further requires that dizygotic pairs are dichorionic; monochorionicity is exclusive to monozygotic pairs. These are fundamental certainties in the literature of twin biology. Multiple observations contradict those common knowledge understandings. The double ovulation hypothesis of dizygotic twinning is untenable. Girl-boy twins differ subtly from all other humans of either sex, absolutely not representative of all dizygotics. Embryogenesis of dizygotic twins differs from singleton development at least as much as monozygotic embryogenesis does, and in the same ways, and the differences between singletons and twins of both zygosities represent a coherent system of re-arranged embryogenic asymmetries. Dizygotic twinning and monozygotic twinning have the same list of consequences of anomalous embryogenesis. Those include an unignorable fraction of dizygotic pairs that are in fact monochorionic, plus many more sharing co-twins' cells in tissues other than a common chorion. The idea that monozygotic and dizygotic twinning events arise from the same embryogenic mechanism is the only plausible hypothesis that might explain all of the observations.

Masculinization of the mammalian cochlea

Otoacoustic emissions (OAEs) differ between the sexes in humans, rhesus and marmoset monkeys, and sheep. OAEs also are different in a number of special populations of humans. Those basic findings are reviewed and discussed in the context of possible prenatal-androgen effects on the auditory system. A parsimonious explanation for several outcomes is that prenatal exposure to high levels of androgens can weaken the cochlear amplifiers and thereby weaken otoacoustic emissions (OAEs). Prenatal androgen exposure apparently also can alter auditory evoked potentials (AEPs). Some non-hormonal factors possibly capable of producing sex and group differences are discussed, and some speculations are offered about specific cochlear structures that might differ between the two sexes.

What Do Sex, Twins, Spotted Hyenas, ADHD, and Sexual Orientation Have in Common?

The otoacoustic emissions (OAEs) measured in a collection of special populations of humans and certain nonhuman species suggest that OAEs may provide a window into some processes of human prenatal development and sexual differentiation. For reasons that are unclear, OAEs appear to be highly sensitive to events occurring during prenatal development that seem to be related to the degree of exposure to androgens a fetus receives. The (largely circumstantial) evidence for a relationship between androgen exposure and OAE strength comes from a series of studies of twins, children with attention-deficit/hyperactivity disorder, people of differing sexual orientations, and spotted hyenas, among others. Some conclusions are bolstered by parallel studies using auditory evoked potentials (AEPs). OAEs and AEPs are simple, objective, noninvasive measures that appear to have potential as tools of value to researchers working on a wide variety of basic and applied topics beyond audition.

Male twins reduce fitness of female co-twins in humans

In mammals, including humans, female fetuses that are exposed to testosterone from adjacent male fetuses in utero can have masculinized anatomy and behavior. However, the reproductive consequences of such prebirth sex-ratio effects for offspring and their implications for maternal fitness remain unexplored. Here we investigate the effects of being gestated with a male co-twin for daughter lifetime reproductive success, and the fitness consequences for mothers of producing mixed-sex twins in preindustrial (1734-1888) Finns. We show that daughters born with a male co-twin have reduced lifetime reproductive success compared to those born with a female co-twin. This reduction arises because such daughters have decreased probabilities of marrying as well as reduced fecundity. Mothers who produce opposite-sex twins consequently have fewer grandchildren (and hence lower fitness) than mothers who produce same-sex twins. Our results are unlikely to be a consequence of females born with male co-twins receiving less nutrition because such females do not have reduced survival and increases in food availability fail to improve their reproductive success. Nor are our results explained by after-birth social factors (females growing up with similarly aged brothers) because females born with a male co-twin have reduced success even when their co-twin dies shortly after birth and are raised as singletons after birth. Our findings suggest that hormonal interactions between opposite-sex fetuses known to influence female morphology and behavior can also have negative effects on daughter fecundity and, hence, maternal fitness, and bear significant implications for adaptive sex allocation in mammals.

[Fetal growth in multiple pregnancy]

A close surveillance of fetal growth in multiple pregnancies is mandatory for the prevention and/or reduction of neonatal morbidity and mortality. Multiples have the same genetically determined growth potential as singletons. However, this growth potential is restricted by the functional capacity of the placenta and uterus. Multiples show a specific growth pattern compared to singletons. Nevertheless, for clinical surveillance, the 10th percentile of singleton growth charts may be used, because significant differences, which may define normally grown multiples as small for gestational age or growth restricted, can only be detected at higher gestational ages, when most of the multiples may have already been delivered. At higher gestational ages, obstetricians should take into account the specific growth pattern for multiples. In multiples with growth discordance, it is necessary to consider or exclude the various causes, and if necessary the clinical follow-up has to be intensified.

Twin differences in birth weight: the effects of genotype and prenatal environment on neonatal and post-neonatal mortality

There is much evidence to suggest that both genes and prenatal environment influence life chances. However, recent within-twin estimates also raise questions about how the influence of genes and prenatal environment may vary across different subgroups of a population and over time. This paper explores such potential variation within the 1st year of life. Using data on twin births from the 1995-1997 Matched Multiple Birth Database and an analytic strategy based on the Weinberg assumption, this paper considers how associations between birth weight and infant mortality vary across identical and fraternal twins, gestational age, and time. Results suggest that the influence of genes and prenatal environment vary most significantly by gestational age. In pregnancies that lasted less than 37 weeks, within-twin variation in prenatal environment is able to account for negative associations between birth weight and infant mortality. However, in pregnancies that lasted 37 weeks or longer, underlying genetic variation across fraternal twins appears to be largely responsible for birth weight-mortality associations. Such distinct findings by gestation suggest that genes and prenatal environment may play varying roles in birth weight-mortality associations across different situations.

Physical and socioeconomic predictors of birthweight in Japan

BACKGROUND

The purpose of this study was to characterize physical and socioeconomic factors associated with birthweight in Tokyo, Japan.

METHODS

In a cohort of obstetric outpatients from the Tokyo Metropolitan Maternity and Child Health Institute, Tokyo, and The Jikei University School of Medicine, Chiba, Japan, 553 eligible women in their third trimester of pregnancy were given a survey investigating physical and socioeconomic backgrounds.

RESULTS

Infants tended to be small for gestational age when maternal pre-pregnancy weight was lower, and low income and female infant gender were significantly associated with a low birthweight infant. Further, birthweight compared with predicted birthweight was lower in the case of a female infant gender, low income, low maternal pre-pregnancy weight and low parity.

CONCLUSION

Income is a novel parameter that is associated with birthweight in Japan.

Gender mix in twins and fetal growth, length of gestation and adult cancer risk

This study evaluated the effect of gender mix (the gender combinations of twin pairs) on fetal growth and length of gestation, and reviewed the literature on the long-term effects of this altered fetal milieu on cancer risk. In singletons, it is well established that females weigh less than males at all gestations, averaging 125-135 g less at full term. This gender difference is generally believed to be the result of the effect of androgens on fetal growth. The gender difference in fetal growth is greater before the third trimester and less towards term, with males growing not only more, but also earlier than females. Plurality is a known risk factor for reduced fetal growth and birthweight. Compared with singletons, the mean birthweight percentiles of twins fall substantially (by 10% or more) below the singleton 10th percentile by 28 weeks, below the singleton 50th percentile by 30 weeks, and below the singleton 90th percentile by 34 weeks. In unlike-gender twin pairs, it has been reported that the female prolongs gestation for her brother, resulting in a higher birthweight for the male twin than that of like-gender male twins. Other researchers have demonstrated that females in unlike-gender pairs had higher birthweights than females in like-gender pairs. Analyses from our consortium on 2491 twin pregnancies with known chorionicity showed longer gestations and faster rates of fetal growth in both males and females in unlike-gender pairs compared with like-gender male or female pairs, although these differences were not statistically significant. The post-natal effects for females growing in an androgenic-anabolic environment include increased sensation-seeking behaviour and aggression, lowered visual acuity, more masculine attitudes and masculinising effects of the auditory system and craniofacial growth. In contrast, there is no evidence to suggest that there might be a similar feminising effect on males from unlike-gender pairs. This hormonal exposure in utero may influence adult body size and susceptability to breast cancer.

Gender mix: does it modify birthweight--outcome association?

Gender mix, especially the supposed hormone transfer in utero of the male fetus to his female co-twin, is a highly debated controversial subject. It occurs in animals (free-martin syndrome in the cow) but its existence in man has not been convincingly demonstrated. Two aspects of gender mix effects in man, birthweight and cognitive development, were studied in the Belgian East Flanders Prospective Twin Survey, a large population-based registry of multiple maternities, characterised by accurate data on pregnancy, placental structure and zygosity. The birthweight of the female member of the pair is not influenced by the male co-twin but, unexpectedly, the female twin enhances to a slight degree the birthweight of her male co-twin by prolonging the gestation for a few days. Also unexpectedly, in an opposite direction, the cognitive development, as measured by the IQ (WISC-R) of the female twin rises as compared with controls if her birthweight exceeds that of her male co-twin.

Growth discordance and the effect of a male twin on birth weight of its female co-twin: a population-based study

There is an ongoing controversy whether the presence of a male twin affects the birth weight of its female co-twin, and if affected, whether birth weights of females are lower or higher in the presence of a male co-twin. The purpose of this study was to study this controversy in a large population of 12,639 twin pairs born in Israel between 1993-1998. Comparison of 7566 females in same-sex (FF) pairs with 4900 females in unlike-sex (FM) pairs, adjusted for the lighter and heavier twin in the pair, showed significantly higher birth weights of females in FM pairs. The same trend was found when concordant pairs and discordant pairs (birth weight difference > 25%) were compared separately. No significant difference was found when 7912 males in same-sex (MM) pairs were compared with 4900 males in FM pairs, adjusted for the lighter and heavier sib. Our study supports a definite intrauterine effect of the male twin on birth weight of its female co-twin. This consequence may potentially be associated with fetal programming of adult disease.

Normal and abnormal growth of multiples

Growth curves of twins and triplets do not support a growth restriction patterns seen in singletons. At the same time that individual members of a twin or a triplet set may be smaller than singletons of the same gestational age, only a minority are indeed SGA by singleton standards. When comparing the entire 'fetal mass' of a multiple pregnancy to that of singletons, multiple gestations are in fact growth promoted, and their individual smaller size are better described as growth adaptation. Data from large twin and triplet series suggest that significant birth weight discordance result from the inability of the uterine milieu to equally nurture twins. In order to promote maturity - gestational age - mild compensation in the form of size discordance begins after mid-gestation. When the uterine environment competently nurtures multiples, total birth weight increases and discordance decreases. Failed adaptation, however, may result in significant growth discordance and restriction.

Strength and anthropometric measures in identical and fraternal twins: no evidence of masculinization of females with male co-twins

Sharing of intrauterine environment in twins of opposite sex has been hypothesized to result in masculinization of the female twin. We tested this hypothesis by comparing strength (maximum hand-grip pressure) and various anthropometric measures in a newly established survey panel comprising 4,314 middle-aged twins identified through a Danish population-based twin registry. Sex- and zygosity-specific mean values of handgrip strength, height, weight, body mass index, and waist circumference were highly comparable between fraternal twins of opposite sex and fraternal twins of same sex. Our results provide no support for the hypothesis of masculinization of female twins from opposite sex twin pairs.