Birth weight discordancy and adverse perinatal outcomes among twin gestations in the United States: the effect of placental abruption

OBJECTIVE: We evaluated whether the relationship between birth weight discordancy of twins and stillbirth, neonatal deaths, and preterm births was modified by the presence of abruption. STUDY DESIGN: We used the 1995 to 1997 matched multiple birth file for United States twin births (n = 269287). Birth weight discordancy was defined as the ratio of the difference in birth weight of the heavier from the lighter twin to that of the heavier twin and was categorized as <5%, 5% to 9%, 10% to 14%, 15% to 19%, 20% to 29%, 30% to 39%, and >or=40%. We evaluated the risks of stillbirth (>or=20 weeks of gestation), neonatal deaths (within 28 days after birth), and preterm birth (< 32 weeks) in the presence and absence of abruption. Associations between birth weight discordancy and these perinatal outcomes were expressed as adjusted relative risks and were derived from multivariable logistic regression models, based on the method of generalized estimating equations. Risk of these outcomes were derived for each stratum of birth weight discordancy and abruption status, with the <5% birth weight discordancy, nonabruption status labeled as the reference group. All analyses were performed separately for same and different sex twins. RESULTS: A birth weight discordancy of >or=20% among same sex (adjusted relative risk, 1.2; 95% CI, 1.1, 1.4), and >or=40% among different sex twins (relative risk, 2.2; 95% CI, 1.7, 2.8) conferred increased risk for abruption. Among nonabruption births, a birth weight discordancy of >or=15% among same sex and >or=30% among different sex twins increased the risk of stillbirths, neonatal deaths, and preterm births. Among abruption births, however, the risks were increased even in the lowest birth weight discordancy category (<5%). The relative risks of stillbirths and neonatal deaths among abruption births were significantly higher for each birth weight discordancy group, both for same and different sex twins, compared with the reference group. The association between birth weight discordancy and preterm birth was not modified by either the presence or absence of abruption. CONCLUSION: Birth weight discordancy of >or=15% for same sex and >or=30% for different sex confer greatest risk of adverse perinatal outcomes in the absence of abruption. In the presence of placental abruption, these risks are further compounded. The results underscore the need for careful monitoring of twin pregnancies.     

Monoamniotic twin pregnancies: antenatal management and perinatal results of 19 consecutive cases

Objective   To describe the obstetric management and perinatal outcome of antenatally diagnosed monoamniotic twin pregnancies (MATP) in a tertiary level maternity unit.
Setting   Port-Royal Maternity Hospital, Paris, France.
Population   MATP that progressed beyond 22 weeks seen from 1993 to 2001.
Methods   A retrospective chart review of all twin pregnancies. Diagnosis of MATP was made by ultrasonography and confirmed by placental pathology.
Main outcome measure   Perinatal mortality.
Results   Among the 1242 twins pregnancies delivered during the study period, 19 were monoamniotic. Four fetuses (10% of all births) had malformations. Perinatal mortality was high ( n = 12, 32%) because of fetal deaths (nine cases) and very preterm births (three neonatal deaths). No fetal deaths occurred after 29 weeks. Of the 15 women with at least one live fetus before labour, 6 gave birth by vaginal delivery (40%). No obstetric accidents occurred during vaginal deliveries.
Conclusion   Perinatal mortality of MATP is still very high, even with accurate, early antenatal diagnosis, intensified surveillance and delivery provided in a tertiary level hospital. The main causes of perinatal deaths are cord accidents in utero , congenital anomalies and very preterm births.     

Perinatal mortality in first- and second-born twins in the United States

OBJECTIVE: To evaluate the prevailing mortality paradox that second-born twins are at higher risk of perinatal mortality than first-born twins. METHODS: We used the 1995-1997 United States "matched multiple birth" data files assembled by the National Center for Health Statistics, for analysis of risk of perinatal mortality in first- and second-born twins (293788 fetuses). Perinatal mortality was defined to include stillbirths after 20 weeks of gestation and neonatal deaths (deaths within the first 28 days). Gestational age-specific risk of perinatal mortality (per 1000 total births), stillbirth (per 1000 total births), and neonatal mortality (per 1000 livebirths) by order of twin birth were based on the fetuses-at-risk approach. Associations between order of birth and mortality indices were evaluated by fitting multivariable logistic regression models based on the method of generalized estimating equations. These models were adjusted for several potential confounding factors. RESULTS: Perinatal mortality was 37% higher in second-born (26.1 per 1000 total births) than in first-born (20.3 per 1000 total births) twins (adjusted relative risk [RR] 1.37; 95% confidence interval [CI] 1.32, 1.42). The increased risk of perinatal mortality in second-born twins was chiefly driven by a 2.46-fold (95% CI 2.29, 2.63) increase in the number of stillbirths. However, the risk of neonatal mortality was very similar between first- and second-born twins (RR 0.99, 95% CI 0.95, 1.04). CONCLUSIONS: The increased risk of perinatal death in second-born twins is driven chiefly by increased rates of stillborn second twins. Thus, the increased mortality in second-born over first-born twins probably is an artifact of mortality comparisons.     

Mode of delivery and the risk of delivery-related perinatal death among twins at term: a retrospective cohort study of 8073 births

OBJECTIVE: To determine the risk of perinatal death among twins born at term in relation to mode of delivery. DESIGN: Retrospective cohort study. SETTING: Scotland 1985-2001. POPULATION: All twin births at or after 36 weeks of gestation, excluding antepartum stillbirths and perinatal deaths due to congenital abnormality (n= 8073). METHODS: The outcome of first and second twins was compared using McNemar's test and the outcome of twin pairs in relation to mode of delivery was compared using exact logistic regression. MAIN OUTCOME MEASURES: Intrapartum stillbirth or neonatal death of either twin. RESULTS: Overall, there were six deaths of first twins and 30 deaths of second twins (OR for second twin 5.00, 95% CI 2.00-14.70). The odds ratio for death of the second twin due to intrapartum anoxia was 21 (95% CI 3.4-868.5). The associations were similar for twins delivered following induction of labour and for sex discordant twins. However, there was no association between birth order and the risk of death among 1472 deliveries by planned caesarean section. There was death of either twin among 2 of 1472 (0.14%) deliveries by planned caesarean section and 34 of 6601 (0.52%) deliveries by other means (P= 0.05, odds ratio for planned caesarean section 0.26 [95% CI 0.03-1.03]). The association was similar when adjusted for potential confounders. Assuming causality, we estimate that 264 caesarean deliveries (95% CI 158-808) would be required to prevent each death. CONCLUSION: Planned caesarean section may reduce the risk of perinatal death of twins at term by approximately 75% compared with attempting vaginal birth. This is principally due to reducing the risk of death of the second twin due to intrapartum anoxia.     

Teenage pregnancies and risk of late fetal death and infant mortality

Objective To estimate the effect of low maternal age on late fetal death and infant mortality and to estimate the extent of any increase in infant mortality attributable to higher rates of preterm birth among teenagers.
Design Population-based cohort study.
Setting Births recorded in the nationwide Swedish Medical Birth Registry.
Population All single births to nulliparous women aged 13–24 years (   n = 320  ,174) during 1973–1989.
Methods Using information recorded in the medical birth registry, linked to a national education register, the effect of low maternal age on adverse outcomes was estimated using logistic regression analysis.
Main outcome measures Late fetal death, neonatal and postneonatal mortality and preterm birth.
Results Compared with mothers aged 2CL24 years, adjusted risks of neonatal and postneonatal mortality were significantly increased among mothers aged 13–15 years (odds ratios = 2.7 and 2.6, respectively) and among those aged 16–17 years (odds ratios = 1.4 and 2.0, respectively), while mothers aged 18–19 years had a significant increase in risk of postneonatal mortality only (odds ratio = 1.4). Rates of very preterm birth (≤ 32 weeks), according to maternal age, were: 13–15 years, 5.9%; 16–17 years, 2.5%; 18–19 years, 1.7%; and 20–24 years, 1.1%. The high rates of very preterm birth among young teenagers almost entirely explained the increased risk of neonatal mortality in this group.
Conclusions The increased risks of neonatal and postneonatal mortality among young teenagers may be related to biological immaturity. The increase in risk of neonatal mortality is largely explained by increased rates of very preterm birth.     

Termination of pregnancy among very preterm births and its impact on very preterm mortality: results from ten European population-based cohorts in the MOSAIC study

Objective  To study the impact of terminations of pregnancy (TOP) on very preterm mortality in Europe.
Design  European prospective population-based cohort study.
Setting  Ten regions from nine European countries participating in the MOSAIC (Models of OrganiSing Access to Intensive Care for very preterm babies) study. These regions had different policies on screening for congenital anomalies (CAs) and on pregnancy termination.
Population or sample  Births 22–31 weeks gestational age.
Methods  The analysis compares the proportion of TOP among very preterm births and assesses differences in mortality between the regions.
Main outcome measures  Pregnancy outcomes (termination, antepartum death, intrapartum death and live birth) and reasons for termination, presence of CAs and causes of death for stillbirths and live births in 2003.
Results  Pregnancy terminations constituted between 1 and 21.5% of all very preterm births and between 4 and 53% of stillbirths. Most terminations were for CAs, although some were for obstetric indications (severe pre-eclampsia, growth restriction, premature rupture of membranes). TOP contributed substantially to overall fetal mortality rates in the two regions with late second-trimester screening. There was no clear association between policies governing screening and pregnancy termination and the proportion of CAs among stillbirths and live births, except in Poland, where neonatal deaths associated with CAs were more frequent, reflecting restrictive pregnancy termination policies.
Conclusion  Proportions of TOP among very preterm births varied widely between European regions. Information on terminations should be reported when very preterm live births and stillbirths are compared internationally since national policies related to screening for CAs and the legality and timing of medical terminations differ.     

Higher perinatal mortality in National Public Health System hospitals in Belo Horizonte, Brazil, 1999: a compositional or contextual effect?

Objective  In Brazil, it was previously reported that in hospital perinatal, neonatal and infant mortality rates are higher for hospitals contracted to the National Public Health System (SUS) compared with non-SUS hospitals. We analyse whether this reflects a compositional effect (selection of patients) or a contextual effect.
Design  Population-based cohort study.
Setting  Belo Horizonte, Brazil, 1999.
Population  A total of 36 469 births in 24 hospitals.
Methods  A multilevel analysis was carried out using information gathered at the individual level on maternal education (used as an indicator of socio-economic status), maternal age, type of pregnancy and delivery, birthweight and sex of the fetus.
Main outcome measure  Perinatal death.
Results  Risk factors for perinatal death included male sex (OR = 1.25; 95% CI 1.01–1.55), birthweight of 1500–2500 g (OR = 7.65; 95% CI 5.74–10.20), birthweight of 500–1500 g (OR = 187.54; 95% CI 141.31–248.39), less than 4 years of maternal education (OR = 2.93; 95% CI 1.68–5.10), as well as birth at private-SUS (OR = 2.92; 95% CI 1.87–4.54) or philanthropic-SUS hospitals (OR = 1.81; 95% CI 1.12–2.92). After controlling for individual characteristics, there was still a significant variation in perinatal deaths between hospitals categories.
Conclusion  Independent of compositional (or individual) characteristics, hospital factors exert an influence on the risk of perinatal death, primarily hospital category related to SUS. Considering the highest proportion of births in SUS hospitals in Brazil, especially private-SUS hospitals, improving hospital quality of care is an urgent priority for reducing the toll of perinatal and infant mortality, as well as inequalities in these outcomes.     

Perinatal outcome and peripartum complications in preterm singleton and twins deliveries: a comparative study

OBJECTIVE: Multiple pregnancy is one of the major risk factors for preterm births. The aim of the present study was to compare perinatal outcome and peripartum complications between twins and singletons, born preterm. STUDY DESIGN: The study population consisted of preterm deliveries of 435 pairs of twins (870 neonates) and the comparison group included 4754 preterm deliveries of singletons, born in the same period (January 1, 1989-December 31, 1996). Exclusion criteria were lack of prenatal care and births following infertility treatments. The three steps in statistical analysis consisted of (1) degree of concordance between the twins; (2) comparison between each twin (I and II) to their singleton comparison groups using SPSS computer program; (3) stratified analysis to examine perinatal mortality rates at different gestational age groups. RESULTS: The prevalence of preterm deliveries was 7.9% (6192/77610). Perinatal mortality was lower in twins of both birth orders, however, it was statistically significant only when APD is considered. Mortality rates in all gestational age groups and for both twin groups were lower than that of singleton [OR=0.45 (0.26-0.75; 95% CI) for twin-I; OR=0.36 (0.21-0.59; 95% CI) for twin-II]. Compared to singletons, twin gestations had less congenital malformations. Twin gestation had statistically lower rates of preterm premature rupture of membranes, severe pregnancy induced hypertension, oligohydramnios, placenta previa, placental abruption and clinical chorioamnionitis [12.2 vs.17.3%, 2.5 vs. 6.3%, 2.3 vs. 4.7%, 0.9 vs. 2.9%, 1.8 vs. 5%, 1.8 vs. 5.2%, respectively (P<0.01)]. Mothers of twins had less diabetes mellitus class B-R, hydramnios and chronic hypertension than that of singleton (1.8 vs. 2.6%, 5.5 vs. 7.4%, 3.7 vs. 4.8%, respectively). Cesarean section rates were significantly higher in twin's gestation. Mothers of twins tended to be older and of higher birth and gravidity order. CONCLUSIONS: Perinatal mortality rates and peripartum complications were lower in twin compared to singleton gestations.     

Causes and consequences of recent increases in preterm birth among twins.

OBJECTIVE: To examine the causes and consequences of the recent increase in preterm birth among twins. METHODS: We studied all twin births among residents of the province of Nova Scotia, Canada, between 1988 and 1997. Rates of preterm birth, preterm labor induction, preterm cesarean, small-for-gestational age (SGA), respiratory distress syndrome (RDS), stillbirth, perinatal mortality, and infant mortality were compared between past and more recent years. Changes in perinatal mortality were examined using logistic regression to adjust for the effects of other determinants. RESULTS: The study included 2516 twin births (73 stillbirths and 2443 live births). The rate of preterm birth increased from 42.3% in 1988-1992 to 48.2% of twin live births in 1993-1997 (14% increase, P =.04). Twin live births born after preterm labor induction increased from 3.5% in 1988-1989 to 8.6% in 1996-1997 (P for trend =.007). Of live births between 34 and 36 weeks' gestation, the proportion born SGA decreased from 17.5% in 1988-1992 to 9.2% in 1993-1997 (P =.005). Over the same period, rates of prophylactic maternal steroid therapy increased substantially and rates of RDS declined. Perinatal mortality rates among pregnancies reaching 34 weeks decreased from 12.9 per 1000 total births in 1988-1992 to 4.2 per 1000 total births in 1993-1997 (P =.05). CONCLUSION: Increases in preterm labor induction appear to be responsible for the recent increase in preterm birth among twins. These changes have been accompanied by decreases in perinatal morbidity and mortality among twin pregnancies that reach 34 weeks' gestation.     

The contribution of assisted conception,chorionicity and other risk factors to very low birthweight in a twin cohort

Objectives To investigate the contribution of assisted conception (assisted reproductive technology and ovulation induction), chorionicity and selected maternal risk factors for very low birthweight.
Design Retrospective twin cohort study.
Setting Staff model Colorado Health Maintenance Organization.
Sample Five hundred and sixty-two twin gestations [assisted = 193 (34%); unassisted = 369 (66%)].
Methods Data were collected from a perinatal database and medical record review. Data were analysed using univariate and multivariable logistic regression analysis.
Main outcome measure Very low birthweight.
Results Women with assisted twin gestation were more likely to be older, nulliparous, non-smokers, married, have a prior history of a miscarriage and a dichorionic placentation. There was no difference in the distribution of low and very low birthweight, discordant growth or preterm delivery between assisted and unassisted twin gestations. Significant risk factors for very low birthweight were: a prior preterm birth (odds ratio, OR, 3.8, 95% confidence interval, CI, 2, 7), monochorionicity (OR 3, 95% CI 2, 4.7), nulliparity (OR 2, 95% CI 1.3, 3), cigarette smoking (OR 1.8, 95% CI 1, 3) and prior miscarriage (OR 1.6, 95% CI 1, 2). Monochorionicity was significantly associated with adverse perinatal outcomes.
Conclusion Assisted conception did not play a significant role in the occurrence of very low birthweight in this cohort. A history of preterm birth and a monochorionic twin gestation were the leading risk factors for very low birthweight. Associated risk factors for very low birthweight were nulliparity, cigarette smoking and a prior miscarriage.     

Role of multiple births in very low birth weight and infant mortality

OBJECTIVE: To determine the percentage of very-low-birth-weight (VLBW) infants (<1500 g) and infant deaths attributable to multiple births in the general population and in women aged 35+. STUDY DESIGN: The year 2000 Massachusetts birth certificate database with linked births-deaths was examined. Etiologic fractions (EF) for VLBW and infant mortality attributable to multiples were calculated for the general population and the 35+ age group. The percentages of multiples occurring in the 35+ age group were calculated. Infant deaths due to congenital anomalies and "perinatal conditions" were calculated. RESULTS: There were 81,582 resident births in Massachusetts in 2000. Of them 4.3% were multiples. Of the 1090 VLBW infants, 26.1% (95% CI: 23.5-28.8) were in twins and 7.7% (95% CI: 6.2-9.5) in higher-order multiples, yielding an EF of 30.8% for multiples in VLBW. In the 35+ age group, the multiple birth ratio was 6.6% (95% CI: 6.3-7.0). The EF for multiples and VLBW in this age group was 33.7%. The 35+ age group accounted for 32.4% (95% CI: 30.8-34.0) of twins and 45.5% (95% CI: 39.1-52.0) of higher-order multiples born in 2000. Of the 392 infant deaths, 57 (14.6%; 95% CI: 11.2-18.4) were attributed to congenital anomalies, and 236 (60.2%; 95% CI: 55.2-65.0) to "perinatal conditions." Multiples were responsible for 8 (14%; 95% CI: 6.3-25.8) of deaths due to anomalies, and 73 (30.9%; 95% CI: 25.1-37.3) due to "perinatal conditions." CONCLUSION: Over 30% of VLBW infants, nearly 20% of infant mortality and >30% of infant mortality due to perinatal conditions could be attributed to multiples. Multiple pregnancy is a significant public health problem.     

Epidemiology of twinning in developed countries

Twin births contribute disproportionately to the overall burden of perinatal morbidity and mortality in developed countries. Twins constitute 2%-4% of all births, and the rate of twining has increased by 76% between 1980 and 2009. The rate of preterm birth (<37 weeks) among twins is about 60%. Of all twin preterm births in the United States, roughly half are indicated, a third are due to spontaneous onset of labor, and about 10% are due to preterm premature rupture of membranes. Mortality related to preterm birth is influenced by antecedent factors and is highest when preterm delivery is the consequence of preterm premature rupture of membranes, followed by those as a result of spontaneous preterm labor and lowest among indicated preterm births. There also appears to have been a recent decline in serious neonatal morbidity (one or more of 5-minute Apgar score <4, neonatal seizures or assisted ventilation for ≥ 30 minutes) among twin gestations. Compared with twins conceived naturally, those born of assisted reproduction methods are more likely to deliver at <37 weeks. Although perinatal mortality rates have declined among twin births, the effect of preterm delivery on trends in mortality and morbidity and other long-term consequences remain issues for major concern. With the rapid increase in the liberal use of assisted reproduction methods combined with women electing to postpone their pregnancies and increased likelihood of spontaneous twins with advancing maternal age, this review underscores the need to develop priorities to understand the peripartum and long-term consequences facing twin births.     

Dietary folate and the prevalence of neural tube defects in the British Isles: the past two decades

Objectives To measure the changes in folate consumption and the prevalence of neural tube defects in the British and Irish populations during the past two decades.
Design Ecological study.
Main outcome measures Average daily dietary folate consumption for Britain for the period 1980–1996 was estimated from the National Food Survey. Annual neural tube defect prevalences for the same period were obtained from the Oxford Record Linkage Study Neural Tube Defect register, the Glasgow EUROCAT register, and the three Irish EUROCAT registers (Belfast, Dublin and Galway).
Results Dietary folate consumption increased on average by 1.6% per annum in Scotland and 1.4% in England during the study period. The annual rate of decline of neural tube defect prevalence averaged 10.4% in the Irish population, 8.2% in Glasgow, and 5.2% in Oxfordshire and West Berkshire.
Conclusions The decline in neural tube defect prevalence observed in all British and Irish populations since the early 1970s continued with the introduction of folate fortification of cereals, which produced measurable increases in average daily folate consumption. Further declines in neural tube defect prevalence may be achieved by targeted folate supplementation during the periconceptual period.     

Twin deliveries and place of birth in NSW 2001–2005

Background:  Twin pregnancies have an elevated risk of adverse outcomes, particularly preterm twins.
Aims:  Describe the distribution of twin deliveries by hospital level, the associated perinatal and maternal morbidity, and determine predictors of perinatal morbidity and urgent transfer to a neonatal intensive care unit.
Methods:  Longitudinally linked New South Wales delivery and hospital records for the years 2001–2005 were used to identify perinatal and maternal morbidity/mortality in twin pregnancies. Regression analysis was used to examine predictive factors, including birth hospital volume.
Results:  At ≤ 32 weeks, 88.1% of twins were delivered in tertiary referral hospitals. By 34–35 weeks, only 39.7% of twins were delivered in tertiary units. Gestational age was the primary predictor of perinatal morbidity/mortality. Perinatal morbidity/mortality and maternal morbidity were lowest for deliveries at 38 weeks. There was no evidence that planned caesarean section at ≤ 38 weeks was protective against perinatal morbidity/mortality. There was an increased risk of perinatal morbidity/mortality (odds ratio (OR) = 2.22) for twins delivered at 33–35 weeks gestation at hospitals with < 500 deliveries per annum, and an increased risk of urgent neonatal transfer (OR = 2.06). Twin pairs for whom there was a ≥ 20% discordance in birthweight had an increased risk of morbidity/mortality at 36–38 weeks (OR = 1.79).
Conclusions:  Both infant and maternal morbidity increase from 39 weeks gestation. Delivery of twins before 36 weeks at smaller hospitals (< 500 deliveries per annum) should be avoided. A twin pregnancy where there is a ≥ 20% difference in estimated fetal weights should be considered for referral to a tertiary obstetric unit.     

Social inequalities in preterm birth in Scotland 1980-2003: findings from an area-based measure of deprivation

Objective  The preterm birth rate in Scotland has been increasing in recent years. Although preterm birth rates show a social gradient, it is unclear how this gradient has been affected by the overall increase. We examined time trends in singleton live preterm birth rates in relation to area-based socio-economic indicators.
Design  Population-based retrospective cohort study.
Setting  Scotland.
Participants  All singleton live births delivered in Scottish hospitals between 1980 and 2003 ( n = 1 423 993).
Main outcome measures  Singleton live preterm birth rates in each deprivation quintile were derived. Subgroup analyses of those born moderately preterm (32–36 weeks), very preterm (28–31 weeks) and extremely preterm (24–27 weeks) were performed.
Results  The rate of singleton live preterm births increased from 49.7 per 1000 live births in the 5-year period 1980–84 to 56.1 per 1000 in the 4-year period 2000–03, a relative increase of 12.9%. A marked social gradient was apparent at all time periods: relative indices of inequality were 1.63 (95% CI 1.38–1.92) in 1980–84 and 1.55 (1.44–1.66) in 2000–03. Similar social gradients existed for all gestational age subgroups. Smoking status at first antenatal contact and increased obstetric intervention, possibly reflecting improvements in fetal monitoring and neonatal care, appeared to explain some but not all the social gradient.
Conclusions  Social inequalities in preterm birth were apparent in Scotland between 1980 and 2003. In addition to helping pregnant women to stop smoking, other means to reduce social inequalities are required.     

Contribution of Gestational Age and Birth Weight to Perinatal Viability in Singletons Versus Twins

The objective of this study was to determine the effects of birth weight and gestational age on twin vs. singleton mortality. Population-based analysis of live births, fetal deaths, and infant deaths by plurality in the United States from 1983 to 1986 was conducted. Seven mortality rates and relative risks (RRs) of twin vs. singleton mortality were calculated by birth weight, gestational age, and combined birth weight and gestational age. The mortality rates included fetal, perinatal, early neonatal, late neonatal, neonatal, postneonatal, and infant. Twins had 3–4 times the RRs of mortality compared to singletons, ranging from a RR of 2.71 for postneonatal mortality to a RR of 3.73 for late neonatal mortality. Generally, for birth weights of 2,800 g or less and gestational ages of 38 weeks or less, twins had lower combined birth weight and gestational age mortality rates and lower RRs. Between 1,900 and 2,799 g, mortality rates decreased then increased with advancing gestation between 31 and 42 weeks both more severely and consistently for twins than for singletons. In conclusion, twins have lower birth weight and gestational age-specific mortality rates and RRs than singletons below 2,800 g and 39 weeks. The “U”-shaped pattern of mortality beyond 38 weeks gestation, particularly for twins with birth weights below 2,500 g, reflects the combined influence of growth retardation and advancing gestation on mortality. The lowest mortalityfor twins is achieved at birth weights of 2,500-2,799gat35-38 weeks gestation. Only 1 in 7 twins is born within this “ideal window.” Efforts at reducing twin mortality should be directed toward reducing intrauterine growth retardation and achieving optimal timing for delivery.     

Low birthweight and preterm birth rates 1 year before and after the Irish workplace smoking ban

Objective  It is well-established that maternal smoking has adverse birth outcomes (low birthweight, LBW, and preterm births). The comprehensive Irish workplace smoking ban was successfully introduced in March 2004. We examined LBW and preterm birth rates 1 year before and after the workplace smoking ban in Dublin.
Design  A cross-sectional observational study analysing routinely collected data using the Euroking K2 maternity system.
Setting  Coombe University Maternal Hospital.
Population  Only singleton live births were included for analyses (7593 and 7648, in 2003 and 2005, respectively).
Methods  Detailed gestational and clinical characteristics were collected and analysed using multivariable logistic regression analyses and subgroup analyses.
Main outcome measures  Maternal smoking rates, mean birthweights, and adjusted odds ratios (ORs) of LBW and preterm births in 2005 versus 2003.
Results  There was a 25% decreased risk of preterm births (OR, 0.75; 95% CI, 0.59–0.96), a 43% increased risk of LBW (OR, 1.43; 95% CI, 1.10–1.85), and a 12% fall in maternal smoking rates (from 23.4 to 20.6%) in 2005 relative to 2003. Such patterns were significantly maintained when specific subgroups were also analysed. Mean birthweights decreased in 2005, but were not significant ( P  = 0.99). There was a marginal increase in smoking cessation before pregnancy in 2005 ( P  = 0.047).
Conclusions  Significant declines in preterm births and in maternal smoking rates after the smoking ban are welcome signs. However, the increased LBW birth risks might reflect a secular trend, as observed in many industrialised nations, and merits further investigations.     

Fetal and neonatal mortality among twin gestations in the United States: the role of intrapair birth weight discordance

OBJECTIVE: To examine the association of intrapair birth weight discordance with fetal and neonatal mortality. METHODS: We used the United States (1995-1997) Matched Multiple Birth File (n = 297,155). RESULTS: Among twin live births and stillborn fetuses, 29.9% had less than 5% birth weight discordance, 24.2% had 5-9%, 29.6% had 10-19%, 11.1% had 20-29%, 3.4% had 30-39%, and 1.8% had 40% or more. The stillborn fetus rate increased progressively with increasing birth weight discordance for smaller and larger twins of the same sex. Compared with the less than 5% birth weight discordance category, the adjusted odds ratios (OR) (95% confidence intervals [CIs]) for stillborn fetus associated with 5-9%, 10-19%, 20-29%, 30-39%, and 40% or more birth weight discordance, respectively, were 0.81 (95% CI 0.58, 1.11), 1.41 (95% CI 1.07, 1.84), 1.74 (95% CI 1.28, 2.35), 3.06 (95% CI 2.21, 4.24), and 4.29 (95% CI 3.05, 6.04) for smaller twins. The corresponding ORs (95% CIs) for larger twins were 0.78 (95% CI 0.57, 1.08), 1.26 (95% CI 0.96, 1.66), 1.77 (95% CI 1.27, 2.46), 3.38 (95% CI 2.33, 4.92), and 2.91 (95% CI 1.89, 4.47). Similar associations were observed among smaller but not larger twins of opposite sex. Among larger but not smaller twins of the same sex, increasing birth weight discordance was associated with overall neonatal deaths. This association was not apparent among smaller and larger twins of opposite sex. However, increasing birth weight discordance was associated with neonatal deaths related to congenital malformations among smaller and larger twins. CONCLUSION: The results provide evidence that increased twin birth weight discordance was associated with increased risk of intrauterine death and malformation-related neonatal deaths.     

In utero nicotine exposure and fetal growth inhibition among twins

We examined the impact of cigarette smoking on fetal growth among twins by analyzing matched twin live births in the United States from 1995 through 1998. The outcomes of interest were low and very low birthweight, preterm and very preterm birth, and small for gestational age. Out of a total of 163,901 mothers, 19,234 reported active smoking during pregnancy (11.7%). Twins born to smokers weighed an average of 182 g less than their counterparts born to nonsmokers (p<0.001). The risk for fetal growth inhibition was greater among twins of smokers: low birthweight (adjusted odds ratio [OR], 1.84; 95% confidence Interval [CI], 1.79 to 1.89), very low birthweight (OR, 1.27; 95% CI, 1.21 to 1.32), preterm (OR, 1.3; 95% CI, 1.09 to 1.16), very preterm (OR, 1.18; 95% CI, 1.13 to 1.23), and small for gestational age (OR, 1.91; 95% CI, 1.84 to 1.98). In conclusion, prenatal smoking significantly inhibits fetal growth among twins, and small for gestational age appeared more affected than shortened gestation.