Mothers Of Twins Research Articles

The prevalence of cobedding and SIDS-related child care practices in twins

Sudden unexplained and unexpected death in twins has not been well studied, particularly in relation to the common practice of sleeping twin infants together in the same cot (cobedding). Postal surveys of 109 mothers of twins were undertaken when the infants were 6 weeks, 4 months, and 8 months of age to determine the prevalence of cobedding, infant care practices related to sudden infant death syndrome (SIDS), and the mother's knowledge of SIDS risk factors. SIDS risk factor knowledge was similar to an earlier survey of singletons in 2005. At 6 weeks, 76% of infants usually slept on the back; this changed to 86% at 4 months and 73% at 8 months. At 6 weeks, 52% usually cobedded with their twin all or part of the time. At 4 and 8 months, this had reduced to 31% and 10%, respectively. Side-by-side cobedding configurations were predominant at 6 weeks, with feet-to-feet configurations increasing as the infants grew older. Breastfeeding was reported in 83%, 61% and 31% of infants at 6 weeks, 4 months and 8 months, respectively. Pacifier use was reported in 38%, 50% and 33% at the respective surveys. As the age of the twins increased, mothers were significantly more likely to be concerned about deformational plagiocephaly in Twin 1 than in Twin 2. Despite a lack of evidence of the risks or benefits of cobedding, this practice was very popular, especially in the younger infants. More research is needed to establish the safety of cobedding in relation to the risk of SIDS.

Impaired production of BMP-15 and GDF-9 mature proteins derived from proproteins WITH mutations in the proregion

Mutations in the bone morphogenetic protein-15 (BMP-15) and growth and differentiation factor-9 (GDF-9) genes have been identified in women with primary ovarian insufficiency (POI) and mothers of dizygotic twins. Here, we show that biological activities of the conditioned media from human embryonic kidney 293F cells transfected with two representative BMP-15 and GDF-9 mutants identified in the affected women have significantly reduced biological activities compared with the corresponding wild-type. Moreover, this difference is due to decreased production of the mature proteins, attributed most likely to impaired posttranslational processing of the proprotein. As genetic studies of the BMP-15 and/or GDF-9 genes in ewes established that a reduction of these proteins is associated with an increased ovulation rate, it is conceivable that women affected with these mutations may have an increased probability of bearing dizygotic twins during active reproductive ages before diagnosis with POI at later ages due to an earlier exhaustion of ovarian reserve.

Body Composition, Smoking, and Spontaneous Dizygotic Twinning

Unlike monozygotic (MZ) twinning, dizygotic (DZ) twinning is influenced by genetic, maternal, and environmental factors. As a result, there are regional and time-dependent differences in its incidence. Established risk factors such as fertility treatments and maternal age do not explain all variation in DZ twinning, and additional factors likely to be involved may include body composition and smoking. In some studies, increasing height and body mass index (BMI) seems to be associated with increased risk of spontaneous DZ twinning, whereas some (but not all) studies report significantly higher multiple birth rates among mothers who smoke. This retrospective cohort study evaluated body composition and smoking before the twin pregnancy among mothers with spontaneous DZ twins; because the rate of MZ twinning is fixed throughout the world, women with MZ twins served as controls. The participants were 19,357 mothers who completed a postal questionnaire as part of the Netherlands Twins Registry, which provided the survey data. The average time between the postal survey and the birth of the twins was 10.4 years. The final study sample was comprised 8515 mothers of spontaneous DZ twins and 5663 mothers of spontaneous MZ twins. Binary logistic regression was used to determine the odds of having spontaneous DZ twins compared to the odds of having MZ twins, after adjusting for independent variables including height, BMI, and smoking before pregnancy, as well as age, gravidity, and educational attainment. Mothers in the tallest quartile for height were 1.6 times more likely than mothers in the shortest height quartile to have DZ twins rather than MZ twins (odds ratio [OR] = 1.6; 95% confidence interval [CI] = 1.5–1.8). Compared to mothers with a normal BMI, overweight or obese mothers were 1.3 times more likely to have DZ twins (OR = 1.3; 95% CI = 1.1–1.4). Twin mothers who had smoked before the twin pregnancy also had an increased likelihood of being a DZ twin mother (OR = 1.4; 95% CI = 1.3–1.5 for smoker vs. nonsmoker). Maternal age and gravidity were associated with spontaneous DZ twinning, but educational attainment was not. These findings are consistent with previous studies showing that spontaneous DZ twinning is associated with maternal body composition and smoking history.

A genome wide linkage scan for dizygotic twinning in 525 families of mothers of dizygotic twins

The tendency to conceive dizygotic (DZ) twins is a complex trait influenced by genetic and environmental factors. To search for new candidate loci for twinning, we conducted a genome-wide linkage scan in 525 families using microsatellite and single nucleotide polymorphism marker panels. Non-parametric linkage analyses, including 523 families containing a total of 1115 mothers of DZ twins (MODZT) from Australia and New Zealand (ANZ) and The Netherlands (NL), produced four linkage peaks above the threshold for suggestive linkage, including a highly suggestive peak at the extreme telomeric end of chromosome 6 with an exponential logarithm of odds [(exp)LOD] score of 2.813 (P = 0.0002). Since the DZ twinning rate increases steeply with maternal age independent of genetic effects, we also investigated linkage including only families where at least one MODZT gave birth to her first set of twins before the age of 30. These analyses produced a maximum expLOD score of 2.718 (P = 0.0002), largely due to linkage signal from the ANZ cohort, however, ordered subset analyses indicated this result is most likely a chance finding in the combined dataset. Linkage analyses were also performed for two large DZ twinning families from the USA, one of which produced a peak on chromosome 2 in the region of two potential candidate genes. Sequencing of FSHR and FIGLA, along with INHBB in MODZTs from two large NL families with family specific linkage peaks directly over this gene, revealed a potentially functional variant in the 5' untranslated region of FSHR that segregated with the DZ twinning phenotype in the Utah family. Our data provide further evidence for complex inheritance of familial DZ twinning.

Mothers of IVF and spontaneously conceived twins: a comparison of prenatal maternal expectations, coping resources and maternal stress

This study explores the differences in prenatal maternal expectations, coping resources and maternal stress between first time mothers of IVF twins and first time mothers of spontaneously conceived twins. The role of prenatal maternal expectations in the prediction of maternal stress was examined, as well as the mediating and moderating effect of coping resources on the association between pregnancy-type group and maternal stress. Mothers of twins from various regions in Israel were included in this prospective and cross-sectional study in which 88 mothers of IVF-conceived twins and 98 mothers of spontaneously conceived twins were interviewed twice. First, at 33-36 weeks of their pregnancy they completed a socio-demographic questionnaire and the maternal expectations questionnaire; then at 6 months after birth they completed a questionnaire regarding the delivery and medical condition of the infants, and their coping resources and maternal stress. Compared with mothers who conceived spontaneously, IVF mothers had more positive prenatal maternal expectations, but poorer coping resources and higher levels of maternal stress 6 months after birth. Maternal expectations had no predictive power regarding maternal stress, although the mother's coping resources were significantly related to maternal stress and mediated the association between pregnancy type and maternal stress. IVF-pregnant women bearing twins should be considered a high-risk group. Early identification of these mothers is essential for timely psychosocial interventions in order to enhance their resources and decrease maternal stress. Further longitudinal studies are required to determine causality in more ethnically-diverse mothers of twins.

Breastfeeding in Preterm and Term Twins—Maternal Factors Associated With Early Cessation: A Population-Based Study

To investigate the duration of breastfeeding and the impact of maternal factors for cessation of breastfeeding in twin infants, the authors undertook a population-based cohort study. Breastfeeding data obtained from Child Health Centres were matched with data on infant and maternal demographics from Swedish national registers. A total of 1.657 twins were included, of whom 695 were born preterm. Breastfeeding frequencies in preterm twins were 79% at 2 months, 58% at 4 months, 39% at 6 months, 14% at 9 months, and 6% at 12 months. In term twins, the corresponding frequencies were 84%, 63%, 45%, 18%, and 6%, respectively. In both preterm and term mothers, mothers who had a lower educational level or smoked at first antenatal care visit were subject to earlier cessation of breastfeeding by 6 months of age. In addition, in mothers of term infants, mothers who were < 23 years old or primiparous had a higher risk for cessation of breastfeeding before 6 months. Thus, mothers of twins have a good potential to breastfeed, but additional support is needed for those more susceptible to early cessation of breastfeeding.

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.

Personal Growth in the Wake of Stress: The Case of Mothers of Preterm Twins

ABSTRACT In a longitudinal study conducted in Israel, the authors compared mothers of preterm twins (n = 64) with mothers of full-term single babies (n = 75) and twins (n = 72). The authors examined the contributions of internal resources (mother's attachment style, mental health, sociodemographic characteristics), external resources (perceived maternal grandmother's support, mother's marital adaptation), and features of the event itself (infant temperament, additional stressful life events, mother's feelings toward her baby or babies) in proximity to the birth, to personal growth 1 year following the birth. Although mothers of preterm twins reported the highest level of negative feelings toward their infants and the lowest level of mental health, they also experienced the greatest personal growth. Younger age and lower level of education, along with higher perceived support from maternal grandmothers contributed to higher personal growth. It seems that in the wake of stress, even mothers who display lower personal resources can rely on their environmental resources and experience personal growth.

128. STRUCTURAL ANALYSIS OF GDF-9 MUTATIONS ASSOCIATED WITH PREMATURE OVARIAN FAILURE AND TWINNING

Premature Ovarian Failure (POF) is a disorder associated with female infertility affecting 1% of women under the age of 40 years [1]. It is characterised by amenorrhea associated with an increase in plasma gonadotrophins and decreased estrogen [2, 3]. The major consequence of POF is the loss of fertility, however women also have increased risk of osteoporosis [4] and cardiovascular disease [5]. The causes of POF are unknown; in recent times genetic factors have been considered as etiological components. Genetic screening of women with POF has identified three mutations in Growth and Differentiation Factor-9 (GDF-9), an oocyte-secreted factor critical for folliculogenesis. These are S186Y, V216M and T238A, which are all located within the GDF-9 prodomain [2]. Mutations in GDF-9 may also contribute to the earlier menopause observed in mothers of dizygotic twins, suggestive of a direct relationship to women with POF [6]. The GDF-9 mutations associated with dizygote twinning (DZ) are; P103S located in the prodomain, and P374L and R454C located within the mature domain [6, 7]. The aim of this study is to understand the consequence of these mutations on the synthesis, secretion and biological activity of GDF-9. Utilising site-directed mutagenesis, all six mutations were individually introduced into GDF-9 cDNA and the impact on protein synthesis and secretion was assessed following transfection in HEK293T cells. Mutants S186Y and T238A appeared to have no affect on mature GDF-9 secretion; mutant R454C resulted in misfolded GDF-9; while mutants V216M, P103S and P374L resulted in a significant decrease of mature GDF-9. As the prodomain is necessary for correct folding, dimerisation and secretion of the biologically active mature protein [8], this decrease is most likely due to the impaired posttranslational processing of the prodomain. In vitro biological activity of these mutants is currently being assessed using a HEK293T cell luciferase reporter assay. Preliminary data suggests that mutants V216M and T238A lead to increased biological activity. It is concluded that GDF9 mutations associated with POF and DZ alter synthesis, secretion and bioactivity of GDF-9. It is anticipated that this study will provide structural basis for the impact of heterozygous GDF-9 mutations on ovarian insufficiency in humans. (1) Dixit, H., et al., Menopause, 2005. 12(6): 749–754.(2) Laissue, P., et al., European Journal of Endocrinology, 2006. 154: 739–744.(3) Pasquale, E.D., et al., The Journal of Endocrinology and Metabolism, 2006. 91(5): 1976–1979.(4) Chand, A.L., et al., Fertility and Sterility, 2006. 86(4): 1009–1012.(5) Chand, A.L., C.A. Harrison, and A.N. Shelling, Human Reproduction Update, 2009: 1–12.(6) Hoekstra, C., et al., Human Reproduction Update, 2008. 14(1): 37–47.(7) Palmer, J.S., et al., The Journal of Clinical Endocrinology and Metabolism, 2006. 91: 4713–4716.(8) Walton, K.L., et al., The Journal of Biological Chemistry, 2010. 285(22): 17 029–17 037.

The Genetics of Preterm Birth: Using What We Know to Design Better Association Studies

Women delivering preterm are at greatly increased risk of another preterm birth in subsequent pregnancies, reflecting effects of the environment, genetics, or both. Recent literature tells an increasingly coherent story about genetic susceptibility. Women who change partners after delivering preterm retain their elevated risk, whereas fathers who change partners do not. Women who themselves were preterm are at increased risk, an association not seen in fathers. Women with a half-sister who delivered preterm are at increased risk only if the shared parent was the mother. Concordance for preterm delivery is elevated in monozygotic compared with dizygotic twin mothers but not in monozygotic twin fathers. Several mechanisms could be operating: mitochondrial genes, maternal genes, or fetal genes expressing only the maternally derived copy. The authors compare 3 study designs for their ability to detect variants and to distinguish among mechanisms underlying heritability of this common outcome. The case-parent triad design offers robustness against self-selection and genetic population stratification, providing for estimation of genetic effects that are fetal, maternal, or that depend on the parent of origin. A case-base approach compares case-mothers with randomly sampled baby-mother pairs and permits estimation of the same relative risk parameters. Both designs offer important advantages over the commonly applied case-mother/control-mother design.

Can an educational DVD improve the acceptability of elective single embryo transfer? A randomized controlled study

To assess whether provision of an educational DVD was more effective in increasing the uptake of elective single embryo transfers (eSET) than an educational brochure in an IVF population. Randomized controlled trial. Private IVF clinic. One hundred thirty-one couples starting their first cycle of IVF were randomized to receive either an educational DVD or brochure. Sixty-four couples received the DVD and 67 couples received the brochure. Both provided identical factual information on outcomes and risks of twin pregnancies. The DVD also included two short interviews with mothers of twins. Preference for eSET after the intervention. There were no significant differences in fertility history or demographics. After the interventions, both groups demonstrated significantly improved knowledge. Patients in the DVD group were significantly more likely to prefer eSET compared with patients who read the brochure (82.6% vs. 66.7%). Patients exposed to the educational DVD were significantly more likely to prefer eSET. Provision of an educational DVD, such as the one used in the present study, may provide an affordable and more effective means of delivering health risk information.

Epidemiology of acephalus/acardius monozygotic twins: New insights into an epigenetic causal hypothesis

Apart from a series of 10 acephalus/acardius (Ac/Ac) cases described from a pathological point of view, and the analysis of a review of published cases, we have been unable to find any epidemiological studies on Ac/Ac. Using data from the Spanish Collaborative Study of Congenital Malformations (ECEMC), we present here what seems to be the first epidemiological analysis of a consecutive series of the Ac/Ac type of monozygotic twins (MZT). Among a total of 2,281,604 consecutive births, 11 cases of Ac/Ac MZT were detected, giving a frequency of 0.48 per 100,000 births. However, we consider the period 1980-1985 as the baseline for our data, as in this period voluntary termination of pregnancy was not possible in Spain, and the frequency of Ac/Ac MZT was 0.49 per 100,000 births. Nonetheless, this frequency should be considered as a minimal estimation. The characteristics of these Ac/Ac cases indicate that they are more frequent in males (sex ratio 2.67). In addition, gestational age in Ac/Ac cases was 2.41 and 3.12 weeks lower than in malformed and control twins, respectively. Similarly, their mothers are 4.54 and 4.68 years younger than mothers of separate malformed and control twins, respectively. To understand the biological basis behind the occurrence of MZT in the context of recent observations, we evaluate the hypothesis that the epigenetic processes involved in the early cleavage of the embryo, and in blastocyst formation during development, may be implicated in twinning.

The rarity of twins: a result of an evolutionary battle between mothers and daughters—or do they agree?

The aim of this study was to test the hypothesis that parent–offspring conflict over parental investment might have led to the rarity of dizygotic twins in humans. We explored the theoretical prediction that twins maximize their inclusive fitness by the death of a co-twin, while mothers of twins maximize fitness by raising both twins to independence. We used life history data (1700–1900) from two parishes in Central Norway to compare differences in inclusive fitness (measured as number of children reared to the age of 16 years, using Hamilton's rule) between twins and mothers of twins. Our results show that twins maximize their inclusive fitness by the death of a co-twin, while mothers of twins raise more children by rearing both twins to adulthood. However, because twins growing up as singletons may produce higher or at least equal number of offspring than the sum of the two twins growing up together, mothers might gain more grandchildren by allowing twins to grow up as singletons. To conclude, both selfish twins and their mothers might benefit by the death of a co-twin, indicating that there is no parent–offspring conflict responsible for the rareness of twins in these human populations. Finally, we discuss the results in the light of “The Insurance Egg Hypothesis” and “The Natural Selection Hypothesis”.

A Recent Rise in Twin Birthrates and Demographic Changes in Mothers of Twins in South Korea: 2003–2007

Using the South Korean national live birth data for the years 2003 to 2007, monozygotic (MZ) and dizygotic (DZ) twin birth rates were estimated and analyzed by maternal age, and parents of twins and those of singletons were compared in their level of education. During this period, while the MZ twin birth rate showed no change, the DZ twin birth rate increased up to 9.4 pairs per thousand births. This rate is close to five times as high as the natural DZ twinning rate in the South Korean population. The highest twinning rate occurred among mothers aged 30 to 34 years, followed by mothers aged 25 to 29. These results represented the first evidence for the downward trend in ages of mothers of twins. In each year between 2003 and 2006, percentages of parents who completed college or higher level of education were higher in the twin than in the singleton group, suggesting that the parental socioeconomic level became higher in twins than in singletons. We speculated that these demographic changes occurred because assisted reproductive technology was more easily available among parents of high socioeconomic status. In their sampling strategies, twin researchers should consider our findings of recent changes in demographic characteristics of parents of twins as well as increased DZ twin birth rates.

Body composition, smoking, and spontaneous dizygotic twinning

To examine differences in body composition and smoking between mothers of spontaneous monozygotic and dizygotic twins, while taking into account maternal age, gravidity, and educational attainment. Retrospective cohort study. The Netherlands Twin Register. Mothers of twins (n = 19,357) registered with the Netherlands Twin Register. Data were selected from mothers of spontaneous monozygotic twins (MZ; n = 5663) and mothers of spontaneous dizygotic twins (DZ; n = 8515). None. The odds of having spontaneous DZ twins versus spontaneous MZ twins as a function of height, body mass index (BMI), and smoking before pregnancy, after accounting for age, gravidity, and educational attainment. Compared with spontaneous MZ twinning, spontaneous DZ twinning is significantly associated with increasing height (odds ratio, 1.6; 95% confidence interval [CI], 1.5-1.8 for the tallest versus the shortest height quartile), an increased BMI (odds ratio, 1.3; 95% CI, 1.1-1.4 for overweight vs. normal weight), and smoking before the twin pregnancy (odds ratio, 1.4; 95% CI, 1.3-1.5 for smoker vs. nonsmoker). Maternal age and gravidity, but not educational attainment, had to be included in the model. Spontaneous dizygotic twinning is associated with body composition and smoking.

Prevalência de nascimentos gemelares em Pelotas, Rio Grande do Sul, Brasil

OBJETIVOS: avaliar a prevalência de nascimentos gemelares em Pelotas, RS, em três períodos da última década e a influência de alguns fatores sobre este processo. MÉTODOS: estudo de corte transversal (série temporal), baseado no banco de dados do Programa de Monitorização de Defeitos Congênitos, onde se encontram registrados todos os nascimentos ocorridos nos cinco hospitais da cidade de Pelotas, nos anos de 1993, 1997 e 2003. RESULTADOS: a taxa média de gêmeos por mil nascimentos foi de 8,95‰ (monozigóticos=2,20‰ e dizigóticos=6,76‰ ). A taxa de triplos ficou em 0,07‰ . A taxa total de nascimentos gemelares, assim como de gêmeos monozigóticos e dizigóticos sofreu elevação no período. A média de idade (27,53 anos) e da ordem gestacional (2,35) das mães de gêmeos foi significativamente mais elevada do que das mães de únicos (26,03 anos e 2,14) respectivamente. Verificaram-se números aproximados de partos gemelares e únicos nos diferentes grupos de renda materna analisados. CONCLUSÕES: as mães com idade maior ou igual a 30 anos foram responsáveis pelo aumento da taxa de gêmeos em Pelotas. A média mais elevada de ordem gestacional em mães de gemelares descartou o uso significativo de técnicas de reprodução assistida.

Mental health of mothers and fathers of twins conceived via assisted reproduction treatment: a 1-year prospective study

Although twin deliveries after assisted reproduction treatment (ART) are common, the mental health of the parents has scarcely been addressed. Therefore, we evaluated the psychological well-being of ART and spontaneously conceiving parents of twins and singletons. Furthermore, the impact of parity and children's health-related factors on mental health was evaluated. We conducted a prospective longitudinal questionnaire study among ART parents of 91 pairs of twins and of 367 singletons and on control parents of 20 pairs of twins and of 379 singletons in the 2nd trimester of pregnancy (T1), and when the children were 2 months (T2) and 1-year old (T3). Symptoms of depression and anxiety, sleeping difficulties and social dysfunction were addressed via a questionnaire. The effects of parity and child-related factors were assessed at T2. At T1, ART mothers of twins showed fewer symptoms of depression than control mothers of twins (P < 0.05). At T2, both ART and control mothers of twins had more symptoms of depression and anxiety than all mothers of singletons (F = 5.20, P < 0.05 and F = 3.93, P < 0.05, respectively). At T3, both ART and control mothers of twins continued to report more symptoms of depression than the mothers of singletons (F = 10.01, P < 0.01), but a difference in anxiety symptoms was seen only in the control group. All fathers had similar mental health at T1. At T2, ART and control fathers of twins reported more symptoms of depression (F = 4.15, P < 0.05) and social dysfunction than fathers of singletons. At T3, both ART and control fathers of twins had more symptoms of depression (F = 4.29, P < 0.05) and anxiety (F = 5.40, P < 0.05) than fathers of singletons. Control fathers of twins had more sleeping difficulties than fathers of singletons (F = 6.66, P < 0.01). Parity did not differently affect parental mental health at T2 in the study groups. Prematurity did not affect maternal mental health, but it had a negative impact on control fathers' social dysfunction (F = 3.34, P < 0.05). Twin parenthood, but not ART, has a negative impact on the mental health of mothers and fathers during the transition to parenthood. ART parents' mental health was not affected by parity or children's health-related factors.

Familial twinning and fertility in Dutch mothers of twins

We studied twinning and fertility indices in mothers with spontaneous monozygotic (MZ) and dizygotic (DZ) twins and in mothers who conceived their twins after the use of assisted reproduction techniques (ART). Participants in this study consisted of 8,222 and 5,505 women with spontaneous DZ and MZ offspring and 4,164 and 250 women with ART DZ and MZ twin pairs, respectively. Women were compared with respect to the number of sibs and offspring, the presence of other relatives with twins and the time it took to conceive the twins. We also compared familial twinning between a younger and an older age group. Women with spontaneous DZ twins more often reported female relatives with twins than those with spontaneous MZ twins. The proportion of DZ versus MZ twin offspring in relatives was also larger in women with spontaneous DZ offspring than in women with MZ offspring. The first group of women reported a shorter time to conceive. Women with ART twins had fewer sibs and offspring and less often reported relatives with twins. We did not observe that DZ twinning was more familial in women who had their twins before age 36 years compared to older women. Familial DZ twinning is clearly present in mothers of spontaneous DZ twins. The mechanisms underlying spontaneous and non-spontaneous DZ twinning are different and fertility treatment should be taken into account in any study of twinning. Twinning is not more familial in women who have their twins at a younger age.

Correlates of Negative and Positive Mood State in Mothers of Twins

Relationships between parenting distress, social support, and sense of competence and negative and positive maternal mood were assessed in 162 mothers with twins younger than 2 years. Women with lower satisfaction scores on the sense of competence scale reported higher negative mood (adjusted R 2 = 21.7%, p < .001). Women with lower parenting distress and higher efficacy scores on the sense of competence scale reported higher positive mood (adjusted R 2 = 39.4%, p < .001). Neither instrumental nor subjective social support contributed to variance in maternal mood. Interventions should be aimed at decreasing parenting distress and increasing sense of competence for mothers of twins.

Twin births, sex of children and maternal risk of endometrial cancer: A cohort study in Norway

To explore whether twin births and sex of children influenced maternal risk of endometrial cancer, possibly with effect modification by age. Population-based prospective study. A total of 1,094,017 parous Norwegian women aged 30-74 years, including 3,356 endometrial cancer cases. Among the 27,158 mothers of twins, 101 cases occurred. Incidence rate ratios (IRR) with 95% confidence intervals (CI) were calculated in Poisson regression analyses of person-years at risk. Women ever having experienced a twin birth had an overall higher risk of endometrial cancer than women with singleton births only (IRR=1.26, 95% CI=1.03-1.53). Women with twin boys appeared to be the main contributor to the overall elevated risk (IRR=1.57, 95% CI=1.15-2.14). The risk estimates for women with twin girls or sex-nonconcordant twins were close to unity (IRR of 1.09 and 1.12, respectively). However, age-specific analyses revealed an elevated risk also in women with twin girls, but only before age 55 years (IRR=1.92, 95% CI=1.27-2.89); a lower risk was seen at older ages (IRR=0.41, 95% CI=0.19-0.92). The risk estimates for twin boys and sex-nonconcordant twins were consistently observed across age groups. The effect modification by age was statistically significant (p=0.0024). No association was found with sex of children in singleton mothers. Mothers of twin boys had a significantly higher risk of endometrial cancer than women with singleton births only, whereas women with twin girls had an elevated risk before age 55 years. No significant association was seen with sex-noncordant twins, neither overall nor within age groups.