The association between the multiple birth and breast cancer incidence: an update of a systematic review and meta-analysis from 1983 to 2022.

BACKGROUND: It has been assumed that perinatal factors such as multiple pregnancies may affect subsequent breast cancer risk in the mother. Considering the inconsistencies in the results of case-control and cohort studies published in the world, this meta-analysis was conducted in order to determine the exact association between multiple pregnancies (twins or more) and the breast cancer incidence. METHODS: This study was performed as a meta-analysis based on PRISMA guidelines by searching the international databases of PubMed (Medline), Scopus, and Web of Science as well as by screening selected articles based on their subject, abstract and full text. The search time was from January 1983 to November 2022. Then the NOS checklist was used to evaluate the quality of the final selected articles. The indicators considered for the meta-analysis included the odds ratio (OR) and the risk ratio (RR) along with the confidence interval reported in the selected primary studies. The desired analyzes were performed with STATA software version 17 to be reported. RESULTS: In this meta-analysis, 19 studies were finally selected for analysis, which fully met the inclusion criteria. Of these, 11 were case-control studies and 8 were cohort ones. Their sample size was 263,956 women (48,696 with breast cancer and 215,260 healthy) and 1,658,378 (63,328 twin or multiple pregnancies and 1,595,050 singleton pregnancies), respectively. After combining the results of cohort and case-control studies, the effect of multiple pregnancies on the breast cancer incidence was equal to 1.01 (95% CI: 0.89-1.14; I2: 44.88%, P: 0.06) and 0.89 (95% CI: 0.83-0.95; I2: 41.73%, P: 0.07), respectively. CONCLUSION: The present meta-analysis results showed, in general, multiple pregnancies were one of the preventive factors of breast cancer.

Mild neonatal morbidity in twins by planned mode of delivery: a secondary analysis of the Twin Birth Study.

BACKGROUND: The Twin Birth Study showed no differences in major severe adverse neonatal outcomes between those with planned vaginal delivery and those with planned cesarean delivery. OBJECTIVE: This was a secondary analysis of the Twin Birth Study in which mild neonatal morbidities, not previously reported, were compared between parturients with planned cesarean deliveries and those with planned vaginal delivery in twin births. STUDY DESIGN: This was a secondary analysis of the Twin Birth Study. In this study, women with a twin pregnancy at 32+0/7 to 38+6/7 weeks of gestation with the first twin in cephalic presentation and with an estimated weight between 1500 and 4000 g were randomized to either planned cesarean delivery or planned vaginal delivery. The primary outcome of this study was a composite mild neonatal outcome of respiratory and neurologic morbidities and neonatal intensive care unit admission that were not reported in the original Twin Birth Study at 34+0/7 to 38+6/7 weeks of gestation. A multivariable logistic regression analysis was used to identify factors associated with the composite adverse neonatal outcomes. Neonatal outcomes were further stratified by gestational age at delivery and by actual mode of delivery. RESULTS: A total of 1304 women and 1326 women were randomly assigned to planned cesarean delivery and planned vaginal delivery, respectively. Demographic and obstetrical characteristics were similar between the study groups. The rate of cesarean delivery was 90.1% in the planned cesarean delivery group and 40.1% in the planned vaginal delivery group. There was no significant difference in the primary composite outcome between the groups (10.6% vs 11.3%; P=.45) neither by planned mode of delivery nor by actual mode of delivery. Stratification by gestational age found a lower rate of the primary outcomes at ≥38+0/7 weeks of gestation in the planned cesarean delivery group when compared with the planned vaginal delivery group (4.8% vs 10.8%, respectively; P=.02). Furthermore, a lower risk for some individual outcomes was reported in the planned cesarean delivery group when compared with the planned vaginal delivery group, including intraventricular hemorrhage stage 1 to 2 (0.2% vs 0.6%; P<.05), low Apgar scores (0.8% vs 2.3%; P<.05), pH <7.0 (0.3 vs 1%; P<.05), and assisted ventilation needed at delivery (0.4% vs 0.9%; P<.05). CONCLUSION: In twin deliveries, with the first twin in the cephalic presentation, composite mild neonatal morbidity was not affected by the planned mode of delivery. These findings reinforce the original results of the Twin Birth Study. Nevertheless, an increased composite outcome after 38 weeks' gestation and a higher risk for some individual morbidities in the planned vaginal delivery group might be viewed as a concerning signal for the safety of vaginal delivery in twin deliveries and requires further research.

Comparing two different placental transfusion strategies for very preterm infants at birth: a matched-pairs study.

OBJECTIVE: To evaluate the clinical outcomes of using the extra-uterine placental transfusion (EPT) approach in very preterm infants (VPIs, gestational age <32 weeks) and compare this to delayed cord clamping (DCC) after birth. METHODS: In this matched pairs study, we compared the clinical outcomes of the EPT group to those of the DCC group. EPT were performed in fifty-three VPIs, of whom 27 were singletons and 25 were twins. The singleton VPIs were matched for gestational age (±5 days) and delivery mode, and the twin VPIs were matched between each other with the first twin subjected to DCC and the second twin to EPT. Data on the infants were collected and analysed as an overall group. A twin subgroup consisting of DCC and EPT groups was also analysed separately. The primary study outcome was either death or major morbidities. RESULTS: In total, 100 infants were included (n = 50 EPT group, n = 50 DCC group). The gestational ages of the DCC and EPT groups were (29.16 ± 1.76) and (29.12 ± 1.84) weeks, respectively. There were no differences in either deaths or major morbidities and other clinical outcomes, including the resuscitation variables, haemoglobin levels and red blood cell transfusion, between the two groups. In twin subgroups (gestational age 29.05 ± 1.89 weeks), EPT was associated with a higher rate of necrotizing enterocolitis (NEC) when compared with DCC (odds ratio = 7 (95% CI, 1.06 to 56.89), p = 0.031). CONCLUSIONS: In twin subgroups, the incidence of NEC was higher in the EPT group when compared to the DCC group and therefore based on an abundance of caution the use of EPT in very preterm twins is not recommended.

Extra-uterine placental transfusion (EPT) is an alternative new form of placental transfusion. It can alleviate the problem of delayed respiratory support during DCC. It can also be performed in some placental abruption cases.EPT may lead to the same clinical outcome as DCC in singleton pregnancies but based on an abundance of caution it is not recommended for very preterm twins.

Twin birth: The maternal experience.

OBJECTIVE: Twin birth is a special setting for women giving birth, and the experience of childbirth can be different from singleton birth. The objective of this study was to evaluate and compare the childbirth experiences of twin mothers and singleton mothers. We also aimed to identify the risk factors of a negative childbirth experience in the whole study population. METHODS: All live diamniotic twin deliveries in the study hospital of at least 35+0 weeks of gestation with a plan of vaginal birth were included in this matched groups study from August 2015 to August 2019. For every twin birth, two singleton birth controls were selected and matched with parity, the actual mode of birth, and gestational weeks at birth. Six weeks after birth, a Childbirth Experience Questionnaire (CEQ) was sent to mothers, and 72 twin mothers and 126 singleton mothers returned the questionnaire. RESULTS: The twin mothers' overall childbirth experience was positive. They reported a significantly lower opportunity to choose the birthing position (p < 0.001). Otherwise, there were no differences in the CEQ mean total scores between the study groups. Intrapartum cesarean section raised the risk of a negative childbirth experience and there was a high level of satisfaction with midwifery care among the whole study population. CONCLUSION: The overall maternal experience in planned vaginal twin birth was positive. Twin mothers felt less often able to choose their birthing position, otherwise the childbirth experience did not differ from that of singleton mothers.

Mode of delivery, perinatal outcome and neurodevelopment in uncomplicated monochorionic diamniotic twins: a single-center retrospective cohort study.

BACKGROUND: There is no agreement on the effect of planned mode of delivery in the perinatal morbidity and neurodevelopment in uncomplicated monochorionic diamniotic as well as regarding the safest mode of delivery. In this paper we have aimed to analyze the impact of the mode of delivery in uncomplicated monochorionic diamniotic twins ≥ 32 weeks of gestation. MATERIAL AND METHODS: This study included 72 women, followed and attended at our department, with uncomplicated monochorionic diamniotic pregnancies who had a birth between 32.0 and 37.6 weeks of gestation from January 2012 to December 2018. Outcomes were recorded in women who underwent planned vaginal delivery (induced or spontaneous onset of labor), and women who underwent a planned cesarean section for any reason that excluded vaginal delivery. Primary outcomes included: (1) A composite of any of the following: neonatal death, 5-min Apgar score < 4, respiratory distress syndrome, bronchopulmonary dysplasia, sepsis, periventricular leukomalacia, intraventricular hemorrhage, and necrotizing enterocolitis. (2) Neurodevelopmental status at 2 years of corrected age. RESULTS: In this period, 42 women (58.3%) had a planned vaginal delivery, and 30 women (41.7%) had a planned cesarean section. In the first group, 64.3% had a vaginal delivery. The rate of successful vaginal delivery was similar regardless the onset of labor. We did not find a higher composite perinatal morbidity in the planned vaginal delivery group (planned vaginal delivery: 3.6% vs. planned cesarean section: 8.3%, aOR 1.36, 95% CI 0.24-7.81). Considering the onset of labor, it was more frequent in the spontaneous subgroup (8.3% vs. 0%). The rate of neurodevelopmental impairment was higher in the planned cesarean section group, without reaching statistical significance [10.2% vs. 4.9%, aOR 1.53 (95% CI 0.37-6.29)]. CONCLUSIONS: In uncomplicated monochorionic diamniotic twins at ≥ 32 weeks of gestation, when the first twin is in vertex presentation, our results suggest that planned vaginal delivery is safe, with a successful outcome as well as high vaginal delivery rate.

The association between maternal complications and small for gestational age in twin pregnancies using singleton and twin birth weight references.

INTRODUCTION: In singleton pregnancies, maternal complications, such as preeclampsia and thyroid dysfunction are associated with small for gestational age (SGA). However, data on the association between SGA and maternal complications in twin pregnancies are limited and conflicting. Small sample size and the application of singleton birth weight reference (SBWR) to define SGA in twins may be reasons for the inconsistent conclusions. Purpose of this study was to define SGA in dichorionic diamniotic (DCDA) and monochorionic diamniotic (MCDA) twin pregnancies using both SBWR and twin birth weight reference (TBWR) and to determine whether certain maternal complications are associated with SGA in twin pregnancies. MATERIALS AND METHODS: This retrospective cohort study included all twins delivered in a single tertiary center between 2013 and 2018. SGA was defined as a twin with birth weight <10th centile for gestational age using either SBWR or TBWR. The association between SGA and maternal complications was analyzed separately for DCDA and MCDA twin pregnancies, expressed as odds ratio (OR) and adjusted odds ratio (aOR) with 95% confidence interval (95%-CI). RESULTS: A total of 2005 DCDA and 467 MCDA twin pregnancies were enrolled. In DCDA pregnancies, SGA was significantly associated with PE according to TBWR (22.73 vs. 14.56%, aOR 1.823, 95%-CI 1.137-2.922). This association was even more pronounced between SGA and severe PE (9.09 vs. 4.54%, aOR 2.234, 95%-CI 1.115-4.479). In turn, PE was associated with higher risk of SGA defined according to TBWR (8.31 vs. 4.99%, aOR 1.825, 95%-CI 1.139-2.925). No association was detected between SGA and other maternal complications. Using SBWR, no association was found between preeclampsia and SGA. In MCDA pregnancies, according to TBWR, SGA was associated only with severe PE (12.5 vs. 4.06%, aOR 3.470, 95%-CI 1.256-9.587) and lower risk of PROM (aOR 0.067, 95%-CI 0.014-0.322). CONCLUSION: PE was associated with SGA in DCDA pregnancies only when TBWR was used, suggesting that DCDA pregnancies complicated with PE should be closely monitored for signs of SGA and vice versa. In MCDA pregnancies, SGA defined according to TBWR was associated with only severe PE (but not with all PE) and lower risk of PROM. More basic experiments are needed to investigate the mechanisms underlying PE and SGA in DCDA and MCDA twin pregnancies respectively.

A rare case of heteropaternal twin calves after natural mating in Brazil.

Twin birth is a complex condition observed in most livestock animals, when the female gives birth to two or more offspring, generally out of the same mating. In cattle, it is a rare condition (3 to 5%) and depends on the genetic background and environmental factors. Twin birth is a result of multiple ovulations, being more common in dairy rather than in beef cattle. Calves could be monozygous or dizygous, with the same or of different sexes. When twins are born with different sexes, a sexual condition called Freemartinism occurs in between 90 to 97% of pregnancies, causing infertility in the female calf. Knowing that the twin rate is rare in commercial beef cattle, here we present an even rarer case of twin birth from two different sires after natural mating, also called heteropaternal superfecundation.

A retrospective study investigating the association of parity, breed, calving month and year, and previous parity milk yield and calving interval with twin births in US dairy cows.

Twinning costs the dairy industry an estimated $96 million each year. Twin pregnancy occurrence in high-producing dairy cows is primarily a result of multiple ovulations associated with low circulating concentrations of progesterone due to high milk production. The present retrospective observational study aimed to identify associations between (1) previous parity milk yield and subsequent twin birth prevalence, (2) twin birth with same parity milk production and calving interval (CInt), and (3) twin birth and the subsequent twin calving. The final data set included almost 2.9 million US dairy calving and production records between 2001 and 2020. Variables considered were parity, breed, milk production, CInt, calving month, and year. Logistic and linear regression modeling were used to assess the effects of predictors on outcomes. Herd within state was used as a random effect for all regression models. Twin birth probability increased for cows with increased previous parity milk yield independent of breed or parity. Third and greater parity (3+) compared with second parity (2) and all breeds compared with Jerseys were associated with greater twin probability. Calving between April and September that corresponded to conceiving in July through December was associated with greater twin birth probability. Twin births were associated with decreased milk production following the birth event in Holsteins and parity 2 cows and in the calving months between June and September. Surprisingly, twin births in parity 3+ cows were associated with an increased 305-d milk yield. Cows that had a twin birth were more likely to calve twins in the subsequent parity and had a greater risk of having a CInt between 413 and 600 d. The hazard to subsequent calving after single births was greater compared with twin births. These data can be instrumental in guiding research focus on reducing twinning in lactating dairy cows.

Impact of mode of delivery on perinatal outcome in moderately and late preterm twin birth.

OBJECTIVE: To examine the impact of the mode of delivery on neonatal and maternal outcomes in moderately and late preterm twin birth. METHODS: This single-center cohort study included 275 live diamniotic moderately and late preterm twin deliveries at 32+0 -36+6  weeks of gestation. These twin deliveries were divided into two groups according to the planned mode of delivery: trial of labor (TOL) (N=199, 72.4%) and planned cesarean section (CS) (N=76, 27.6%). The primary outcome was neonatal morbidity. Maternal outcome and the effects of gestational age and chorionicity on neonatal outcome were also studied. RESULTS: Of the women in the TOL group, 170 (85.4%) delivered vaginally. Both for the first and second twin, and for dichorionic or monochorionic deliveries, there were no differences between the TOL and CS groups in composite neonatal morbidity or in other neonatal outcomes. No significant differences were found between the TOL and CS groups when the moderately and late preterm gestational age cohorts were studied separately. Mothers in the planned CS group more often had puerperal infection and surgical complications in comparison with mothers in the TOL group. CONCLUSION: Among 275 moderately and late preterm twin deliveries, planned mode of delivery did not affect neonatal outcome.

Risk factors of unsuccessful vaginal twin delivery.

INTRODUCTION: Twin trial of labor presents a challenge to obstetricians, as it is associated with a greater number of adverse birth outcomes compared with singleton deliveries. The risk of poor outcome has shown to be highest with unsuccessful vaginal twin delivery. The purpose of this study was to identify the clinical risk factors associated with intrapartum cesarean section in late preterm and term twin births. MATERIAL AND METHODS: All live diamniotic twin deliveries of at least 35+0 weeks of gestation with planned vaginal delivery were included in this retrospective single-center cohort study. Maternal and newborn characteristics were compared between a vaginal delivery group and an intrapartum cesarean section group. Logistic regression analysis was carried out to determine independent risk factors of intrapartum cesarean section. Further, maternal and neonatal outcomes were compared between groups of vaginal delivery and cesarean section for both twins and also between groups of vaginal delivery and cesarean section for the second twin only (combined delivery). The impact of presentation of the second twin on the mode of twin delivery and on neonatal outcome was also examined. RESULTS: Among 821 twin pregnancies, 581 mothers (70.8%) attempted trial of labor and were eligible for the study. With a cephalic-presenting first twin, the trial of labor rate was 89.3% and vaginal delivery was successful in 82.8%. Nulliparity (odds ratio [OR] 3.2, 95% confidence interval [CI] 2.0-5.1) and non-cephalic presentation of the second twin (OR 3.0, 95% CI 1.9-4.8) were found to be independent risk factors of cesarean section. However, 76.1% of mothers with non-cephalic second twins achieved vaginal delivery and perinatal outcomes were comparable with cases of cephalic-presenting second twins. When comparing delivery modes, maternal outcomes were more favorable with vaginal delivery, whereas combined delivery increased the second twin's risk of adverse neonatal outcome. CONCLUSIONS: This study, with high rates of trial of labor and successful vaginal twin delivery, found nulliparity and non-cephalic presentation of the second twin to be risk factors of intrapartum cesarean section in twin pregnancies.

Mode of birth in twins: data and reflections.

Our primary objective was to compare neonatal and maternal outcomes in women with twin pregnancies, beyond 32 weeks, having a planned vaginal birth or a planned caesarean section (CS). This was a retrospective cohort study from a single tertiary centre over nine years. 534 sets of twins ≥32 + 0 weeks of gestation were included. 401 sets were planned vaginally and 133 sets were planned by CS. We compared a composite adverse perinatal outcome (perinatal mortality or serious neonatal morbidity; five minute APGAR score ≤4, neurological abnormality and need for intubation) and a composite maternal adverse outcome (major haemorrhage, trauma or infection) between the groups. There were no significant differences. Given the similarity of these results with several other larger studies of twin birth, we sought to look at reasons why there is still a rising rate of CS for twin births. We further make suggestions for keeping this rate to a sensible minimum. Impact statement What is already known on this subject? The largest randomised controlled study comparing planned vaginal birth with planned CSs for lower risk twins between 32 and 39 weeks of gestation, showed no added safety from planned CS. However, in most of the Western countries this conclusion has failed to increase the number of planned vaginal births for lower risk twins. What do the results of this study add? This observational study from a single tertiary centre provides external validation of the twin trial results in a practical day-to-day setting. It also provides insights as to how planned vaginal birth can be developed and maintained, with a key focus on safety and maternal participation in decision making. It does focus on consent and providing accurate data. What are the implications of these findings for clinical practice and/or further research? There are good grounds to encourage vaginal birth for low-risk twin pregnancies. The trend of rising caesarean rates in low-risk twin pregnancies worldwide will erode important skills for the conduct of vaginal births without any clear benefit for mothers or babies. The current situation demands careful thought about implementing innovative training opportunities for younger obstetricians. Finally, we need intelligent responses to many non-evidence-based factors which can drive clinical practice.

Embryo cryopreservation and preeclampsia risk.

OBJECTIVE: To determine whether assisted reproductive technology (ART) cycles involving cryopreserved-warmed embryos are associated with the development of preeclampsia. DESIGN: Retrospective cohort study. SETTING: IVF clinics and hospitals. PATIENT(S): A total of 15,937 births from ART: 9,417 singleton and 6,520 twin. INTERVENTION(S): We used linked ART surveillance, birth certificate, and maternal hospitalization discharge data, considering resident singleton and twin births from autologous or donor eggs from 2005-2010. MAIN OUTCOME MEASURE(S): We compared the frequency of preeclampsia diagnosis for cryopreserved-warmed versus fresh ET and used multivariable logistic regression to adjust for confounders. RESULT(S): Among pregnancies conceived with autologous eggs resulting in singletons, preeclampsia was greater after cryopreserved-warmed versus fresh ET (7.51% vs. 4.29%, adjusted odds ratio = 2.17 [95% CI 1.67-2.82]). Preeclampsia without and with severe features, preeclampsia with preterm delivery, and chronic hypertension with superimposed preeclampsia were more frequent after cryopreserved-warmed versus fresh ET (3.99% vs. 2.55%; 2.95% vs. 1.41%; 2.76 vs. 1.48%; and 0.95% vs. 0.43%, respectively). Among pregnancies from autologous eggs resulting in twins, the frequency of preeclampsia with severe features (9.26% vs. 5.70%) and preeclampsia with preterm delivery (14.81% vs. 11.74%) was higher after cryopreserved versus fresh transfers. Among donor egg pregnancies, rates of preeclampsia did not differ significantly between cryopreserved-warmed and fresh ET (10.78% vs. 12.13% for singletons and 28.0% vs. 25.15% for twins). CONCLUSION(S): Among ART pregnancies conceived using autologous eggs resulting in live births, those involving transfer of cryopreserved-warmed embryos, as compared with fresh ETs, had increased risk for preeclampsia with severe features and preeclampsia with preterm delivery.

Higher Rates of DZ Twinning in a Twenty-First Century Birth Cohort.

The Colorado Twin Registry is a population based registry initiated in 1984 with the involvement of the Colorado Department of Health, Division of Vital Statistics. Recruitment includes birth cohorts several years prior to 1984 and all subsequent years. As part of a recent evaluation of Colorado birth records for the years 2006 through 2008 we became aware of a shifting trend in the proportion of MZ and DZ twins in the Colorado population. Historically (Bulmer 1970 The biology of twinning in man, Clarendon, Oxford) we have expected a 1/3, 1/3, 1/3 ratio of MZ, same-sex DZ and opposite sex DZ twins in Caucasian populations. An excess of MZ pairs in most studies was assumed to be due to selection bias. Somewhat more recently, Hur et al.(1995 Behav Genet 25, 337-340) provided evidence that the DZ twinning rate was falling and that therefore selection bias was not the reason for higher MZ enrollment in most twin studies. They suggested that twin researchers might consider strategies to over-enroll DZ pairs to maximize statistical power. In contrast, we now find that of the 3217 twin births in Colorado from 2006 to 2008 with identified sex information the MZ rate is estimated at only 22%, and we have corroborating reports from other states of similar estimates. These were calculated applying Weinberg's rule which assumes an equal birth rate for same sex and opposite sex DZ pairs so that the proportion of MZ in a sample is the proportion of same sex (MM + FF) minus the proportion of opposite-sex (MF, FM). We explore factors, such as an increase in the proportion of non-Caucasian parents and an increase in average maternal age, which may contribute to this shift.

Term twin birth - impact of mode of delivery on outcome.

INTRODUCTION: The main aims of this study were to compare maternal and neonatal outcomes in term twin birth according to the planned mode of delivery and to study the effects of chorionicity and inter-twin delivery time on neonatal outcome. MATERIAL AND METHODS: A single-center cohort study of 495 women with twin deliveries at ≥37+0 weeks of gestation. Term twin deliveries were divided into a trial of labor group (TOL, 69.3%) and a planned cesarean section (CS) group (30.7%). The primary outcomes were maternal and neonatal morbidity. RESULTS: 80.8% of women attempting TOL achieved vaginal birth. In the TOL group, mothers had less bleeding [median 500 mL (range 150-2700 mL) vs. 950 mL (range 150-3500 mL), p < 0.001) and fewer surgical complications (3.2% vs. 8.6%, p = 0.011), whereas second twins more often had five-minute Apgar scores of <7 (5.0% vs. 0%, p = 0.002) or umbilical artery pH < 7.05 (5.7% vs. 0%, p = 0.003), compared with the planned CS group. There was a slight, non-significant tendency for more NICU admissions in the TOL group, yet the need for NICU treatment was infrequent in the whole study material. Outcomes among dichorionic (DC) second twins were similar to those in the whole material, but among monochorionic (MC) second twins there were no differences between the TOL and planned CS groups. In secondary analysis, a five-minute Apgar score <7 occurred significantly more often in the DC group among second twins if the inter-twin delivery time exceeded 30 min. CONCLUSIONS: TOL is a good option for women with twin pregnancy at term, regardless of chorionicity. Active management of labor for the second twin is important, also in DC births. Maternal outcomes were more favorable with TOL and although low Apgar scores and low umbilical blood pH may be more frequent after TOL - especially with the second twin - serious neonatal morbidity is rare and does not differ from that after planned CS.

A Natural Twin Hospital Birth: My Birth Story.

In this column, the author describes the vaginal birth of her twin daughters. Despite impending complications in the last weeks of her pregnancy that might have required a cesarean, this mother was committed to doing everything possible to give birth naturally. With the support of her husband as well as the obstetrician and the nurse, she was able to give birth to her daughters vaginally.

Exploring Women's Preferences for the Mode of Delivery in Twin Gestations: Results of the Twin Birth Study.

OBJECTIVE: The Twin Birth Study, an international, multi-center randomized controlled trial was conducted to compare the risks of planned cesarean with planned vaginal delivery for twin pregnancies. The aim of this component of the trial was to understand participants' perspectives of study participation and preferences for the mode of delivery. METHODS: A mixed-methods questionnaire was distributed to study participants 3 months after giving birth. The questionnaire contained Likert scales and open-ended questions about the experience of being enrolled in a clinical trial and of childbirth, including the mode of delivery. Quantitative data were analyzed using SAS to generate descriptive statistics. Qualitative data were analyzed to identify categories and themes. RESULTS: Ninety-one percent of trial participants completed the questionnaire. Across all groups, the majority of women would participate in a study like this one again if given the opportunity. Main benefits of participating were as follows: benefits to one and one's babies, altruism, and receiving quality care. Randomization for the mode of delivery was challenging for women because of the desire to be involved in decision-making. Findings related to childbirth experience and the mode of delivery demonstrated a preference for vaginal birth across all groups. Those who had a vaginal birth were more satisfied with their birth experience. CONCLUSIONS: This study provides evidence to inform practitioners about what women who have twin pregnancies like or dislike about birth and their desire for involvement in decision-making. Vaginal birth was preferred across all study groups and was associated with greater satisfaction with childbirth experience.

Genetic analysis of twinning rate and milk yield using a threshold-linear model in Japanese Holsteins.

The objective of this study was to estimate genetic parameters and breeding values for the twinning rate of the first three parities (T1, T2 and T3) and 305-day milk yield in first lactation (MY), using a four-trait threshold-linear animal model in Japanese Holsteins. Data contained 1 323 946 cows calving between 1990 and 2007. Twinning was treated as a binary character: 'single' or 'twin or more'. Reported T1, T2 and T3 were 0.70%, 2.87%, and 3.73%, respectively. Individual 305-day milk yield was computed using a multiple trait prediction for cows with at least eight test-day records. (Co)variance components were estimated via Gibbs sampling for randomly sampled subsets. Posterior means of heritabilities for T1, T2 and T3 were 0.11, 0.16 and 0.14, respectively. Genetic correlations between parities were 0.92 or greater. Genetic correlations of MY with twinning rate were not 'significant' (i.e. their 95% highest probability density intervals contained zeros). Multiple births at different parities were considered as the same genetic trait. The average evaluations of T1 (T2) for sires born before 1991 was 0.48% (2.25%) compared with a mean of 0.76% (3.37%) for sires born after 1992. A recent increase in the reported twinning rate reflects the positive genetic trend for sires in Japanese Holsteins.

Twin Birth Considering the Current Results of the "Twin Birth Study"

The rate of caesarean sections in multiple births has grown sharply worldwide. The reason for this may be the results of large retrospective cohort studies from the 1990s, which displayed an increased risk of mortality and morbidity, especially for the second twin, in the case of vaginal births. Multiple monocentric analyses have not been able to confirm this. As a prospective, multi-centre randomised study, the Twin Birth Study published in 2013, in which 105 clinics in 25 countries took part, showed that, under optimum conditions, there was no difference in neonatal and maternal mortality and morbidity if the birth was planned to be vaginal or via caesarean. Detailed analyses, which would be helpful in choosing the type of birth method and obstetric management in the event of vaginal birth, have not previously been published. Retrospective studies must be referred to for this.

Twin delivery: method, timing and conduct.

The incidence of twin pregnancy has increased worldwide over the past 10 years, largely as a consequence of the assisted reproductive technologies. Issues such as intrapartum monitoring and operative interventions, especially relating to the second twin, provide a unique challenge in labour and delivery. Epidemiological and cohort data suggest that twins have a three-fold higher mortality rate than singletons, and that the second twin might have a better outcome if delivered by lower segment caesarean section. The recently completed Twin Birth Study has found that planned vaginal lower segment caesarean section is not advantageous to the fetus. In the light of this large randomised-controlled trial, vaginal delivery if twin A presents by the vertex is recommended as long as guidelines for the conduct of such delivery are followed.

Impact of monozygotic twinning on multiple births resulting from in vitro fertilization in the United States, 2006-2010.

OBJECTIVE: To determine the contribution of monozygotic twining to in vitro fertilization multiple births. STUDY DESIGN: We performed a retrospective analysis of the incidence of monozygotic twining in multiple births resulting from fresh embryo transfers using 2006-2010 data from the Society for Reproductive Technology Clinic Outcome Reporting System. RESULTS: The number of embryos transferred were fewer than the number of births in 0.5% (223/40950) of twin, 29% (659/2289) of triplet, and 64% (43/67) of quadruplet births resulting from transfer of fresh embryos from 2006 to 2010. In 2010, 37% of triplets and 100% of quadruplet births occurred when fewer than 3 and fewer than 4 embryos respectively were transferred. CONCLUSION: Monozygotic twinning plays a key role in the development of triplet and quadruplet pregnancies achieved through in vitro fertilization.