Unlike-sex Pairs Research Articles

Hypertensive disorders during monozygotic and dizygotic twin gestations: A population-based study

ABSTRACTObjective: To determine whether the incidence of hypertensive disorders is different in monozygotic compared to dizygotic twin pregnancies. Methods: A registry-based survey of twin pregnancies delivered during 2003 to 2012. We used the best clinical estimate of zygosity based on the concept that all monochorionic twins are monozygotic and all unlike-sex pairs are dizygotic, thus excluding same-sex dichorionic twin gestations for which zygosity cannot be ascertained on clinical grounds. Study cohorts were twin pregnancies with or without preeclampsia and gestational hypertension. Results: A total of 3419 twin gestations met the inclusion criteria, of which 442 (12.9%) were monochorionic and 1255 (36.7%) were unlike-sex twins, excluding 1722 same-sex dichorionic twin gestations (50.4%). There was no significant difference in the incidence of preeclampsia (OR: 0.9; 95% CI: 0.4–2.0 for monozygotic males and OR: 0.6; 95% CI: 0.3–1.4 for monozygotic females) and gestational hypertension (OR: 0.7; 95% CI: 0.2–2.5 for monozygotic males, and OR: 0.7; 95% CI: 0.2–2.3 for monozygotic females) between monochorionic and unlike-sex pairs. Maternal prepregnancy obesity and nulliparity were the only significant associated factors of preeclampsia (OR: 3.8; 95% CI: 2.0–7.0, and OR: 2.5; 95% CI: 1.4–4.4, respectively). Maternal prepregnancy obesity (OR: 5.5; 95% CI: 2.5–12.2), maternal age ≥36 years (OR: 2.5; 95% CI: 1.1–6.1), and family history of hypertension (OR: 2.6; 95% CI: 1.3–5.1) were significantly associated with gestational hypertension. Conclusion: Based on a large population-based dataset and on the best clinical estimate of twin zygosity, it appears that zygosity is not associated with hypertensive disorders in twin gestations.

Behavioral correlates of depressive symptoms in older unlike-sex twin pairs

This study examines gender-specific behavioral correlates of depressive symptoms using a secondary data analysis of a cross-sectional, population-based sample of older unlike-sex twins. Unlike-sex twins aged 69-88 were identified through a national Swedish registry and sent a survey about health, including depressive symptoms (CES-D) and the frequency of engaging in physical, social and mental activities. A total of 605 complete twin pairs responded. Depressive symptom scores were associated with frequency of engagement in physical and mental activities, but only in men. No statistically significant associations with depressive symptom scores for any of the three types of activities were found in women. The results suggest that engaging in physical and mental activities may protect older men from developing depressive symptoms, but longitudinal data are needed to offer more conclusive findings on the role that physical, mental, and social activities play in the maintenance of psychological health in older men and women.

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. 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. 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). 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.

Gestation and Birthweight in Dizygotic Twins: Girls Call the Tune

AbstractUnlike-sex twins provide a unique natural experiment to investigate the influence of sex on gestation. Our data showed that length of gestation of unlike-sex pairs is similar to that of female same-sex pairs, and significantly (0.4 wks,p= .02) longer than that of male same-sex pairs. Birthweight of female unlike-sex twins was similar to female same-sex twins, but male unlike-sex twins weighed 78 g more than male same-sex twins (p= .001). These data show that in unlikesex pairs it is the girl that prolongs gestation for her brother, resulting in a higher birthweight than that of same-sex boys.

“Masculinizing” Effect on Respiratory Morbidity in Girls From Unlike-Sex Preterm Twins: A Possible Transchorionic Paracrine Effect

Preterm male infants are at a disadvantage when compared with female infants regarding the incidence of respiratory and neurologic morbidity and mortality. At term, female infants from unlike-sex twin pairs have birth weights that are closer to their male co-twins than to girls from like-sex twin pairs. We hypothesized that if the male disadvantage is mediated via factors that affect fetal lung development, there may be a potential effect on the incidence of respiratory distress syndrome and its complications in female infants from unlike-sex pairs. In this population-based study we used data from the Israel Neonatal Network, which included data from 8858 very low birth weight (500-1500 g) infants of 24 to 34 weeks' gestation. The incidence of morbidity and mortality was compared in male and female infants from singletons and like-sex and unlike-sex twin pairs. Multivariable analyses were used, accounting for relevant confounding variables. Male singletons and like-sex twins were at increased risk for mortality, respiratory distress syndrome, pneumothorax, bronchopulmonary dysplasia, periventricular-intraventricular hemorrhage, and periventricular leukomalacia. However, in unlike-sex twin pairs, no difference was seen in the incidence of respiratory morbidity between male and female twins. The male disadvantage was maintained for mortality and periventricular-intraventricular hemorrhage. These findings suggest that the difference in morbidity and mortality between male and female premature infants represents a male disadvantage as opposed to a female advantage and that this disadvantage may be transferred from boys to girls in unlike-sex twin pairs, perhaps via an intrauterine paracrine effect.

A note on cluster headache in a population-based twin register.

Evidence of a familial risk factor in cluster headache is accumulating and studies of twin concordance may resolve family resemblance into genetic and environmental influences. The past literature on cluster headache in twins comprises a few case reports of concordant monozygotic pairs. Swedish twin pairs with a diagnosis of cluster headache were selected through a cross-match of national registers of twin births and hospitalizations. Seventeen discordant twin pairs were found, in which it was possible to verify cluster headache status in 11 complete pairs (two monozygotic, four dizygotic, and five unlike-sexed pairs). In both members of a female monozygotic pair, migraine without aura developed after birth of the first child and remitted by menopause, whereas post-menopausal development of chronic cluster headache occurred in only one of them. The importance of individual specific factors for cluster headache was demonstrated. However, to explain familial aggregation a larger sample of affected twin pairs is necessary.

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.

Fetal or infant death in twin pregnancy: neurodevelopmental consequence for the survivor

Aim: To determine the neurodevelopmental morbidity in the surviving twin after fetal or infant death of the co-twin. Methods: Twin pregnancies with an antepartum or infant death delivered between 1981...

Length of gestation and birthweight in dizygotic twins

Despite the longer gestation of girls, their birthweight is less than that of boys. Because unlike-sex twins provide a natural situation in which to investigate the influence of sex on gestation, we compared birthweight and gestation of 1929 same-sex and unlike-sex dizygotic pairs. Length of gestation in unlike-sex pairs was similar to that of female same-sex pairs, and significantly (0.4 weeks; p=0.02) longer than that of male same-sex pairs. Birthweight of girls from unlike-sex pairs was similar to that of girls from same-sex pairs, but boys from unlike-sex pairs weighed 78 g more than boys from same-sex pairs (p=0.001). These data show that in unlike-sex pairs it is the girl that prolongs gestation for her brother, resulting in a higher birthweight than that of same-sex boys.

Adaptive Growth Restriction as a Pattern of Birth Weight Discordance in Twin Gestations

In Brief Objective To challenge the hypothesis that discordant growth is a normal variation by relating birth weight discordance to total twin birth weight. Method Among 12,565 Israeli live-born twin pairs (1993–98), we compared total twin birth weight decile, the frequencies of three levels of discordance in the general population, over 25% discordance between like- versus unlike-sex pairs, and over 25% discordance between pairs delivered by primiparas versus multiparas. Results We found a marked change in the best-fit correlation function with increased discordance: level 15–24.9% was inversely linear whereas levels 25–34.9% and over 34.9% were inversely logarithmic (R2 = .47, .88, and .9, respectively). The best-fit correlation of frequencies of more than 25% discordance was inversely logarithmic and similar in like-and unlike-sexed twins across deciles functions (P = .7, odds ratio [OR] 1.0, 95% confidence interval [CI] 0.9, 1.2). The overall frequencies of discordance were also similar (9.3% versus 10.2%, P = .11, OR 0.9, 95% CI 0.8, 1.0). The frequencies of primiparas decreased linearly (R2 = .98) and the frequencies of more than 25% discordant pairs in multiparas and primiparas across the deciles had similar inversely logarithmic patterns (P = .55, OR 1.0, 95% CI 0.9, 1.2). Discordance over 25% was significantly more frequent among primiparas (P < .001, OR 1.45, 95% CI 1.3, 1.6). Conclusion The observed patterns of birth weight discordance did not substantiate normal variation but an adaptive growth restriction that might explain why the likelihood of discordant growth decreases as total twin birth weight increases. Intertwin birth weight discordance patterns suggest an adaptive growth restriction whereby the larger the total twin birth weight, the smaller the likelihood of discordant growth.

Adaptive growth restriction as a pattern of birth weight discordance in twin gestations

Objective: To challenge the hypothesis that discordant growth is a normal variation by relating birth weight discordance to total twin birth weight. Method: Among 12,565 Israeli live-born twin pairs (1993–98), we compared total twin birth weight decile, the frequencies of three levels of discordance in the general population, over 25% discordance between like- versus unlike-sex pairs, and over 25% discordance between pairs delivered by primiparas versus multiparas. Results: We found a marked change in the best-fit correlation function with increased discordance: level 15–24.9% was inversely linear whereas levels 25–34.9% and over 34.9% were inversely logarithmic ( R 2 = .47, .88, and .9, respectively). The best-fit correlation of frequencies of more than 25% discordance was inversely logarithmic and similar in like- and unlike-sexed twins across deciles functions ( P = .7, odds ratio [OR] 1.0, 95% confidence interval [CI] 0.9, 1.2). The overall frequencies of discordance were also similar (9.3% versus 10.2%, P = .11, OR 0.9, 95% CI 0.8, 1.0). The frequencies of primiparas decreased linearly ( R 2 = .98) and the frequencies of more than 25% discordant pairs in multiparas and primiparas across the deciles had similar inversely logarithmic patterns ( P = .55, OR 1.0, 95% CI 0.9, 1.2). Discordance over 25% was significantly more frequent among primiparas ( P < .001, OR 1.45, 95% CI 1.3, 1.6). Conclusion: The observed patterns of birth weight discordance did not substantiate normal variation but an adaptive growth restriction that might explain why the likelihood of discordant growth decreases as total twin birth weight increases.

Epidemiology of familial sarcoidosis in the UK.

The last comprehensive epidemiological studies on familial sarcoidosis in the UK were more than 25 years ago, reporting another affected family member in 1.7% of index cases. A significant proportion of like-sex over unlike-sex pairs, an excess of mother-child over father-child associations, and a preponderance of monozygous over dizygous twins was noted. Another study reported ethnic heterogeneity in familial disease. This study was undertaken to identify the risk ratio (lambda(S)) for siblings of familial sarcoidosis in the UK, to determine if the previous epidemiological findings have persisted, and to reassess whether ethnic heterogeneity prevails in familial disease. Questionnaires were sent to 406 index patients. Two hundred and sixty eight replies (66%) were received. Twenty four of the original 406 index patients (5.91%) were found to have at least one other relative (first, second or third degree) with biopsy proven sarcoidosis. A lambda(S) value of 36-73 was calculated indicating significant familial clustering of the disease. Ethnically the families comprised 62.5% Caucasian, 29.2% Afro-Caribbean, and 8.3% Asian. Mean age at diagnosis was 39.8 years for women and 40.9 years for men with a male to female ratio of 1:1.7. This differed for the Asian families in which all the affected members were male. Three sets of female twins (two monozygous and one dizygous) were included. There was an equal distribution of like-sex (primarily female) and unlike-sex families as well as mother-child and father-child pairs. Pulmonary involvement was predominant irrespective of ethnicity, as was the need for corticosteroid treatment. These results support the theory that a shared determinant (either genetic or environmental) is operating in familial sarcoidosis and suggest that this determinant is similar for all ethnic groups.

The uterine capacity measured by the total twin birth weight and duration of twin pregnancy.

The objective of this study was to answer the question whether there is the relation between the uterine capacity, estimated by the total birth weight of fetuses, and the duration of twin gestation. The material for researches contains data received from the books of births and case records concerning the pregnant who gave births to twins in the Institute of Obstetrics and Gynecology of the Medical University in Lódź between 1970-1998. The final analysis concerned only gestations lasting more than 29 weeks, without any complications (excluding prematurity and the growth-discordant twins), and when gestational age was exactly known. The selected group was finally composed of 188 pairs of twins. The analyses considered relations between total birth weight of twins, the sex of newborn babies, parity, and the duration of gestation. The duration of the analyzed twin pregnancies was 35.6 weeks, including primiparous with 35.8 weeks, and multiparous--35.1 weeks. In the group of male-male twin pairs the average duration of pregnancy was 35.7 weeks, in unlike-sexed pairs--35.6 weeks, and in female-female pairs--35.5. In the group of the primiparous having male-male twin pairs the average duration of pregnancy was 35.1 weeks, unlike-sexed pairs--36.4 weeks and female female pairs--36.6 weeks, while in the group of multiparous relatively: 36.4, 35.4, 35.0 weeks. The total birth weight of the specific pairs of twins was from 2270 g to 6900 g (average 4794 g), while in 92% < 5500 g. In the primiparous group it was 4908.1 g. and in the multiparous group--4663.1 g. Analyzing the total twins' weight according to the fetal gender and parity it was found that in primiparous with male-male twins--4715.3, unlike-sexed--5271.6 and female-female--4967.5, whereas in multiparous relatively: 4961.5, 4692.6, 4414.0. The shortening of twin pregnancies was caused by the following factors: total body mass achieved by fetuses was > 5500 g, presence of male sex in twin pregnancies (only in primiparous), and also the multiparity.

Time trends in twin perinatal mortality in northern England, 1982–94

AbstractThe dynamics of perinatal mortality rates (PNMR) and causes of death in twin pregnancies over 13 years in the Northern Region of the National Health Service in England is described. All twin perinatal deaths occurring between 1982–1994 were identified from the Northern Region Perinatal Mortality Survey. The twinning rate increased from 9.9 per 1000 maternities in 1982 to 12.0 in 1994. There was a total of 10734 twin pregnancies and of these 421 resulted in 530 perinatal deaths. The perinatal mortality rate in twins significantly decreased over time (1982–87, 55.4 per 1000; 1988–94, 44.4 per 1000; P = 0.01). The PNMR was significantly higher for twins from like-sexed than from unlike-sexed pairs (53.5 and 34.4 per 1000 respectively, P &lt; 0.001). Despite no improvement in birthweight distribution in the twin population, birthweight-specific perinatal mortality rates for both like and unlike-sexed twins decreased for each birthweight category in 1988–94 compared with 1982–87. Twins with very low birthweight ( &lt; 1500 g) comprised 69%, and preterm twins ( &lt; 37 completed weeks of gestation) 74.9% of all twin perinatal deaths. The major immediate cause of early neonatal death was pulmonary immaturity (63%); antepartum anoxia caused 76.9% of antenatal deaths. Unexplained preterm labour and intrauterine death were the leading obstetric factors underlying death in twins. Despite a decrease over the 13 years, the perinatal mortality rate in twins in the Northern Region remains high. Continued monitoring of trends in twinning and mortality rates is needed to inform health care planning.

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

There is evidence to suggest a masculinizing effect on female intrauterine development in unlike-sexed twins. The purpose of the present report was to examine the possible effects of male presence on fetal growth in females by comparing mean birthweights in members from dizygotic unlike-sexed (DZU) pairs with those from dizygotic like-sexed (DZL) pairs. The sample consisted of 1087 DZU and 1089 DZL twin pairs from the New Norwegian Twin Panel, which was established by identifying all twin births from 1967 to 1974 through the population-based Medical Birth Registry. The mean birthweight of females from DZU pairs was 2684+/-15 g (+/-SEM), as opposed to 2647+/-19 g in females from DZL pairs (P = 0.06). For males, the mean birthweight was 2812+/-16 g in DZU pairs and 2805+/-20 g in DZL pairs (P= 0.78). We found a tendency for the birthweight in females to be influenced by the presence of a male co-twin. This observation may have a biological significance and should lead to a close follow-up of DZU and DZL females with respect to hormone-sensitive disorders and reproductive ability.

Birth weight discordancy in twins: New definition and standard

Objective. The aim of this study was to improve the definition of birth weight discordancy based on its distribution in the population after a correction in the unlike sex pairs. Study Design. The analysis was conducted on 849 Italian twin pairs. Male's birth weight in the unlike sex pairs was corrected by the physiological birth weight difference estimated on 21.595 Italian twins data. Birth weight discordancy was computed as a percentage of the larger twin's birth weight and it was compared by sex pairs and by gestational ages (Kruskal–Wallis test). Kolmogorov–Smirnov test was used to fit a normal distribution to the square-root transformed birth weight discordancy. Results. The estimated physiological birth weight difference between males and females was 4.39%, without any difference among gestational ages. The 90th centile of birth weight discordancy was 23.9% and the 95th centile was 29.2%. Conclusions. Ninetieth and 95th centiles of the fitted distribution are proposed as cut-off values for the definition of mild and severe birth weight discordancy.

Influence of gender on susceptibility to multiple sclerosis and age of onset in concordant sibships.

Research has produced conflicting findings about whether there is an excess of like-sexed pairs among concordant multiple sclerosis (MS) sibships. Although a positive correlation in onset age among sibling pairs overall has been reported, no data have been published describing age at onset correlations for like-sexed versus unlike-sexed pairs. The purpose of this study was to provide additional information on both issues. Patients with an MS sibling were sought through the files of the University of Alberta MS clinic (Edmonton, Canada). The clinic neurologist either reviewed clinical/autopsy material or assessed relatives of index cases prior to accepting the relative as having MS. Pairs of siblings (excluding twins) were divided into (1) male-male pairs, (2) female-female pairs, and (3) female-male pairs. A total of 62 concordant sibling pairs were identified. There were 33 like-sexed pairs (6 male-male/27 female-female) and 29 unlike-sexed pairs. The observed number of like-sexed pairs was not significantly different from the expected frequency using 2 x 2 chi2 analysis, where expected values represent the binomial distribution predicted from the frequency of each sex as determined by total number of males and females. The age at onset intraclass correlation coefficient was -0.09 for sibling pairs overall, -0.22 for like-sexed pairs and +0.02 for unlike-sexed pairs. This study does not provide evidence for an association between disease susceptibility and gender in siblings concordant for MS; nor does it suggest that genetics plays a role in onset age.

Childhood neurological disorders in twins.

In order to examine neurological outcome in twins, a multi-centre prospective cohort study of infants was used. Women entered at the first prenatal visit, with follow-up of offspring to the age of 7 years. Outcome measures were death, cerebral palsy, seizure disorders including neonatal, febrile or nonfebrile, and intelligence quotient. Among a total of 52,364 livebirths, there were 1079 twins. Overall, rates of fetal or neonatal death and cerebral palsy were higher in twins. Neonatal and febrile seizures occurred with similar frequency in twins as in singletons. Although twins were much more likely than singletons to be low in birthweight, twins < 2500 g were not at higher risk for cerebral palsy than low birthweight singletons. The risk of cerebral palsy and of nonfebrile seizure disorders was similar in monozygous and dizygous pairs, and in like-sex and unlike-sex pairs. Death of one twin was associated with higher rates of cerebral palsy and of nonfebrile seizure disorders in survivors, but not with lowered intelligence. Data from this cohort suggest that low birthweight and survival status of the co-twin are dominant predictors of childhood neurological morbidity in twins.

Some perinatal characteristics of monozygotic twins who are dichorionic

Zygosity testing of all multiple births allowed the identification of a subgroup of 42 monozygotic twin pairs who have dichorionic placentas, fused and separate. Perinatal outcomes of this group were compared with 110 pairs of monochorionic monozygotic twins and 148 pairs of dizygotic twins. Dichorionic monozygotic twins had the lowest incidence of preterm birth, perinatal mortality, and birth weight discordance. There was an excess of like-sexed over unlike-sexed pairs among the dizygotic twins.

Sex-specific causal factors and effects of common environment for symptoms of anxiety and depression in twins.

Two thousand five hundred seventy intact pairs and 724 single responders from Norwegian twins aged 18-25 years completed questionnaires with information about anxiety and depression and perceived cotwin closeness. The aim of the study was the univariate estimation of sex-specific genetic and environmental effects on an index tapping symptoms of anxiety and depression. An index of social closeness between cotwins was significantly related to the cotwin correlation for anxiety/depression scores. MZ pairs were reported to be closer than DZ pairs, and like-sexed DZ pairs were closer than unlike-sexed pairs. The symptom data were adjusted for this apparent violation of the "equal-environment" assumption in twin studies, but the adjustment did not dramatically affect the parameter estimates of genetic and environmental effects on anxiety/depression. A model specifying male (aM) and female (aF) genetic additive effects, shared environment for males (cM), and individual environmental effects (eM and eF) fitted the adjusted data very well. An alternative model, specifying aM = aF, cM = cF, and eM = eF, and no correlation between those environmental factors shared by brothers and those shared by sisters, fitted equally well. Estimated proportions of total variance from the first model were aM2 = .30, aF2 = .52, and cM2 = .21. The estimates from the second model were aM2 = aF2 = .43 and cM2 = cF2 = .11.