Biomedical subjects

S W Wen

Publications and source records attributed to S W Wen.

At least 19 recordsLinked to original sources

PubMed2006

Paternal age and birth defects: how strong is the association?

BACKGROUND: Although the association between maternal age and the risks of birth defects has been well studied, the evidence from population data linking paternal age with birth defects was limited and inconsistent. METHODS: We conducted a population-based retrospective cohort study of 5,213,248 subjects from the 1999-2000 birth registration data of the USA. Multiple logistic regressions were used to estimate the independent effect of paternal age on all birth defects and 21 specific defects groups after adjusting for potential confounding of maternal age, race, education, marital status, parity, prenatal care initiation, maternal smoking and alcohol drinking during pregnancy. RESULTS: A total of 77,514 (1.5%) birth defects were recorded in the study cohort. The adjusted odds ratios were 1.04 (1.01, 1.06), 1.08 (1.04, 1.12), 1.08 (1.02, 1.14) and 1.15 (1.06, 1.24), respectively, for infants born to fathers 30-35, 40-44, 45-49 and over 50 years (test for trend, P = 0.0155), when compared with those infants born to fathers aged 25-29 for any birth defect. Advanced paternal age was associated with increased risks of heart defects, tracheo-oesophageal fistulaoesophageal atresia, other musculoskeletal/integumental anomalies, Down's syndrome and other chromosomal anomalies. Fathers under 25 years of age were also at increased risks of spina bifida/meningocele, microcephalus, omphalocele/gastroschisis and other musculoskeletal/integumental anomalies. CONCLUSIONS: Infants born to older fathers have a slightly increased risk of birth defects. Young paternal age is also associated with slightly increased risk of several selected birth defects in their offspring. However, given the weak association, paternal age appears to play a small role in the aetiology of birth defects.

Adult↗

PubMed2006

Semen quality in a residential, geographic and age representative sample of healthy Chinese men.

BACKGROUND: Population-based study of semen quality is rare in literature. METHODS: Healthy men aged 20-60 years from six Chinese provinces were invited to participate in the study between December 2000 and November 2002. Posters were distributed in the participating counties to enroll 200 subjects from each province. Medians, percentiles, and proportions below lower threshold of the WHO criteria for semen parameters were calculated. Generalized linear models were used to examine the determinants of semen quality. RESULTS: Semen samples from 1191 healthy Chinese men were collected and analysed. The medians (5th and 95th percentiles) were 2.3 ml (1.0-4.5) for semen volume, 65 x 10(6)/ml (20-150) for semen concentration, 154 x 10(6)/ejection (29-421) for sperm count, 19% (5-32) for rapid progressive motility, 46% (29-66) for progressive motility, 67% (47-81) for total motile spermatozoa, 70% (48-88) for sperm viability and 39% (23-76) for normal morphology. Many healthy Chinese men had semen parameter values below the lower threshold of the WHO criteria. Region, age, abstinence duration and season were important determinants of semen quality. CONCLUSIONS: Chinese men have lower values of semen parameters according to WHO standard, and a lower threshold for normal semen parameters for Chinese men should be considered.

Adult↗

PubMed2006

Pregnancy-induced hypertension is associated with lower infant mortality in preterm singletons.

OBJECTIVE: To assess the association between pregnancy-induced hypertension (PIH) and infant mortality. DESIGN: Retrospective cohort study. SETTING: Birth and infant death registration dataset of the USA. POPULATION: A total of 17,432,987 eligible, liveborn singleton births in 1995-2000. METHODS: Multivariate logistic regression was applied to evaluate the association between PIH and infant mortality, with adjustment of potential confounders. MAIN OUTCOME MEASURES: Infant death (0-364 days) and its three components: early neonatal death (0-6 days), late neonatal death (7-27 days), and postneonatal death (28-364 days). RESULTS: There was a significant reduction in infant mortality associated with PIH in early preterm infants (OR = 0.59, 95% CI: 0.56-0.63) and in late preterm infants (OR = 0.80, 95% CI: 0.73-0.87), but a significant increase in term infants (OR = 1.08, 95% CI: 1.02-1.14). Both in early preterm and late preterm births, early neonatal mortality (OR = 0.38, 95% CI: 0.34-0.42; OR = 0.68, 95% CI: 0.61-0.77) and late neonatal mortality (OR = 0.59, 95% CI: 0.50-0.70; OR = 0.76, 95% CI: 0.61-0.96) were decreased in infants born to mothers with PIH compared with those born to mothers with normal blood pressure. The PIH-associated reduction in neonatal mortality among preterm singletons was stronger in small-for-gestational-age infants than in normal growth infants and stronger in infants born to nulliparous women than in those born to multiparous women. CONCLUSIONS: PIH is associated with lower risk of infant death in preterm births but higher risk in term births.

Adult↗

PubMed2006

Neonatal mortality and morbidity in vertex-vertex second twins according to mode of delivery and birth weight.

OBJECTIVE: To assess the risk of neonatal mortality and morbidity in vertex-vertex second twins according to mode of delivery and birth weight. STUDY DESIGN: Data from a historical cohort study based on a twin registry in the US (1995-1997) were used. Multivariate logistic regression was used to control for maternal age, race, marital status, cigarette smoking during pregnancy, parity, medical complications, gestational age, and other confounders. RESULTS: A total of 86 041 vertex-vertex second twins were classified into two groups: second twins delivered by cesarean section after cesarean delivery of first twin (C-C) (43.0%), second twins whose co-twins delivered vaginally (V-X) (57.0%). In infants of birth weight>or=2500 g group, the risks of noncongenital anomaly-related death (adjusted odds ratio (aOR): 4.64, 95% confidence interval (95% CI): 1.90, 13.92), low Apgar score (aOR: 2.39, 95% CI: 1.43, 4.14), and ventilation use (aOR: 1.31, 95% CI: 1.18, 1.47) were higher in the V-X group compared with the C-C group. No asphyxia-related neonatal deaths occurred in C-C group, whereas the incidence of this death was 0.04% in the V-X group. CONCLUSION: The risks of neonatal mortality and morbidity are increased in vertex-vertex second twins with birth weight>or=2500 g whose co-twins delivered vaginally compared with second twins delivered by cesarean section after cesarean delivery of first twin.

Adult↗

PubMed2006

Survival analysis of liver transplant patients in Canada 1997-2002.

UNLABELLED: Liver transplantation is an important health care issue for Canadians. Very few studies have assessed survival and determinants of survival in liver transplant patients in Canada. METHODS: We carried out an epidemiological analysis of 1 year survival and determinants of 1 year survival in liver transplant patients, using Canadian Organ Replacement Registry data (1997-2002). Survival curves were plotted by the Kaplan-Meier method. Cox proportional hazards analysis was applied to evaluate hazard ratios with different age groups, gender, ethnicity, blood groups, donor type, pretransplantation medical status, and HBV infection status. RESULTS: A total of 1164 liver transplant patients were included in the analysis. One-year survival rate was 84.7%. Male recipients had a 21% higher risk of developing organ failure than females. Recipients over 60 years of age had a 5% lower survival probability in comparison with recipients below 20 years of age. Pacific Islanders and Aboriginals had 32% and 9% lower survival probabilities, respectively, in comparison with Caucasians. Type B blood recipients had a 12% higher survival probability, whereas type AB blood recipients had a 7% lower survival probability compared with type O blood recipients. Twenty-six live organ recipients had 40% higher survival probabilities than 1138 cadaveric organ recipients. Patients with fulminant hepatitis (status 3F) had the highest survival, while patients with fulminant failure in ICU with intubation/ventilation (status 4F) had the lowest survival. One hundred sixty-seven recipients with positive HBsAg antigen showed 10% lower survival probability than 997 cases with negative HBsAg antigen. CONCLUSION: In Canada, the first year survival rate is about 85%, which is comparable with other industrialized countries. Type of donor organs and recipient gender, ethnicity, ABO blood group, pretransplantation medical status, and HBV infection status had significant affects on the recipient survival.

Canada↗

PubMed2004

The effect of a disastrous flood on the quality of life in Dongting lake area in China.

We carried out an epidemiological study to assess the impact of flood on the quality of life (QOL) of residents in the affected areas in China. We used a natural experiment approach, randomly selected 494 adults from 18 villages, which suffered from flooding as a result of embankments collapsing, 473 adults from 16 villages, which suffered from, soaked flood, and 773 adults from 11 villages without flood (control group). We used the Generic QOL Inventory-74 (GQOLI-74), social support scale, and questionnaires to assess the QOL of all study participants. The QOL was significantly poorer in soaked group (58.4) and (especially) in collapsed group (55.1) than in control group (59.5, p<0.001). Adjustment for potential confounding factors did not change the results. The impact of flood on QOL was stronger among farmers, seniors, persons with introvert personality, and residents with adverse life-events, whereas social support and extrovert personalities offset the negative impact of flood on QOL.

Adult↗

PubMed2001

Detecting and eliminating erroneous gestational ages: a normal mixture model.

In perinatal research and clinical practice, gestational age is a crucial variable for measuring foetal 'growth' (birth weight for gestational age) and for estimating the risk of mortality and morbidity, yet reported gestational age values are affected by random and systematic errors due to the absence of a gold standard measure. Previous investigators have used birth weight (which is measured with greater validity and precision than is gestational age) to correct such errors, but existing methods are inadequate due to unreasonable assumptions about the distributions of birth weight and gestational age. We propose a new method for identifying and correcting implausible observations using the expectation-maximization (EM) algorithm. Using population-based data from U.S. birth certificates, we compare the resulting gestational ages, birth weight distributions at each gestational age, and gestational age-specific infant mortality based on the new method with those on the same population produced by previous published correction methods. The new method gives the best birth weight distributions for gestational age and the most realistic gestational-age-specific mortality rates, while each of the other methods has at least one significant flaw.

Algorithms↗

PubMed2001

Secular trends in congenital anomaly-related fetal and infant mortality in Canada, 1985-1996.

Prenatal diagnosis of major congenital anomalies and subsequent termination of affected pregnancies has been widely available as part of routine obstetric care in recent years. In this study, vital statistical data on stillbirths, live births, and infant deaths were used to examine secular trends in gestational age-specific and category-specific fetal and infant mortality due to congenital anomalies in Canada (excluding Ontario and Newfoundland) from 1985-1996. Comparisons of the rates between 1985-1987 and 1994-1996 were made using relative risks and 95% confidence intervals (CI). The overall fetal mortality rate due to congenital anomalies increased significantly, from 68.0 per 100,000 total births in 1985-1987 to 78.6 per 100,000 total births in 1994-1996, while the overall infant mortality rate due to congenital anomalies decreased significantly over the same period, from 2.47 to 1.79 per 1,000 live births. The fetal death rate due to congenital anomalies at 20-21 weeks of gestation increased approximately five-fold (relative risk [RR] = 4.83, 95% CI = 3.28-7.11) from 4.5 to 21.5 per 100,000 fetuses at risk, while the rate at 37-41 weeks decreased by 30% (RR = 0.70, 95% CI = 0.50-0.97). Fetal death rates among pregnancies at 20-25 weeks of gestation increased in all categories of congenital anomaly except anencephaly and respiratory system anomalies. Congenital anomaly-related fetal and infant deaths have increased at early gestation but declined at later gestation in Canada. These changes suggest an increase in prenatal diagnosis and selective termination of pregnancies with congenital anomalies in recent years.

Canada↗

PubMed2001

The effect of income pooling within a call group on rates of obstetric intervention.

BACKGROUND: On July 1, 1997, the call group at a tertiary referral hospital in Ottawa changed its remuneration. The authors tested the hypothesis that change in an obstetric call group's remuneration from individual fee-for-service billing to equal sharing of the pooled group income would result in reduced rates of obstetric intervention. METHODS: Intervention rates were compared for the 12 months before (1678 births) and the 12 months after (1934 births) the change. Data were collected on onset of labour, indication for induction of labour, mode of delivery and neonatal outcome. Statistical analysis was performed with Wilcoxon's signed-rank test. RESULTS: The mean rate of elective induction of labour was 38.6% in the year before the change and 33.3% in the year after the change (p = 0.01). There were small but statistically significant increases in the mean duration of labour and mean length of the second stage (p = 0.03). INTERPRETATION: Billing policy may affect clinical decisions. Our findings add weight to the literature showing increased intervention rates with fee-for-service remuneration.

Decision Making↗

PubMed2001

Comparison of maternal and infant outcomes between vacuum extraction and forceps deliveries.

The authors conducted a population-based historical cohort study in the Canadian province of Quebec to assess the maternal and infant outcomes associated with vacuum extraction and forceps deliveries. The study database contains information on 305,391 mother-infant dyads (linked by a common institutional code and hospital chart number) for singleton live vaginal births with a nonbreech presentation at the gestational age of 37 or more completed weeks and a birth weight between 2,500 and 4,000 g during fiscal years 1991/1992 to 1995/1996. Of the births, 31,015 were delivered by vacuum extraction, and 18,727 were delivered by forceps. Compared with delivery by forceps, the adjusted risk ratios for third-/fourth-degree perineal laceration, intracranial hemorrhage, subdural or cerebral hemorrhage, intraventricular hemorrhage, subarachnoid hemorrhage, cephalhematoma, and neonatal in-hospital death were 0.48 (95% confidence interval: 0.45, 0.50), 1.28 (95% confidence interval: 0.73, 2.25), 0.97 (95% confidence interval: 0.49, 1.93), 0.99 (95% confidence interval: 0.16, 5.97), 5.44 (confidence interval: 1.26, 23.43), 2.02 (95% confidence interval: 1.89, 2.16), and 0.93 (95% confidence interval: 0.32, 2.70), respectively. The authors conclude that vacuum extraction causes less maternal trauma but may increase the risk of cephalhematoma and certain types of intracranial hemorrhage (e.g., subarachnoid hemorrhage).

Adult↗

PubMed2001

Implausible birth weight for gestational age.

Various rules have been proposed to identify and exclude live births with implausible values of birth weight for gestational age from large perinatal data sets. The authors carried out a preliminary evaluation of common rules by examining the frequency and nature of rule-based exclusions among live births in Canada (excluding Ontario) between 1992 and 1994. There were 625 (0.09%), 133 (0.02%), 170 (0.02%), and 2,858 (0.40%) live births identified for exclusion by a median birth weight for gestational age +/-4 standard deviations (SD) rule, a +/-5 SD rule, a rule based on expert clinical opinion, and a modification of Tukey's rule, respectively. The birth weight and gestational age distribution of the exclusions depended on the particular rule used; for example, 12.1% and 0.3% of live births of > or =4,500 g were excluded under Tukey's rule and the rule based on expert opinion, respectively. Infant mortality rates among those excluded were 8-13 times higher than among all live births. Current rules for identifying implausible birth weight for gestational age tend to flag live births at high risk for infant death. Such rules may erroneously attenuate temporal trends in important perinatal outcomes.

Algorithms↗

PubMed2001

Adverse outcomes in pregnancies of asthmatic women: results from a Canadian population.

PURPOSE: There has been little attention paid to asthma complicating pregnancy. This study is among the few studies that investigated this issue in a large Canadian population (more than two millions of Canadian pregnant women). METHODS: We carried out a historical cohort study using hospital discharge data collected by the Canadian Institute for Health Information for fiscal years 1989/90 to 1995/96. RESULTS: A total 2,017,553 obstetric deliveries were included in the analysis. Overall prevalence of asthma among these Canadian women were 0.43%, yielding a total of 8672 cases of asthmatic mothers. Maternal asthma was associated with all of the adverse pregnancy outcomes examined (including fetal death, preterm labour, hypertensive disorders of pregnancy, gestational diabetes, antepartum hemorrhage, infection of the amniotic cavity, premature rupture of membrane, cesarean delivery, as well as postpartum hemorrhage), and adjustment for important confounding factors by multiple logistic regression analysis did not change the overall results. These associations were consistently observed in teenage and adult mothers, although the associations in teenage mothers tended to be stronger than in adult mothers. CONCLUSIONS: This study confirms that pregnant women with asthma are at substantially increased risk for many adverse pregnancy outcomes. For this reason, pregnant women with asthma are a particularly high-risk group to which extra attention, including increased efforts at education, monitoring, and optimal asthma management, may be appropriate.

Adolescent↗

PubMed2001

The impact of national health insurance on the utilization of health care services by pregnant women: the case in Taiwan.

OBJECTIVES: Substantially increased funding for health care services occurred in Taiwan after the implementation of a national health insurance plan in 1995. This study attempts to examine the impact of this national health insurance plan on the utilization of prenatal and intrapartum care services. METHODS: Nationally representative surveys of all pregnant women in Taiwan in 1989 (1,662 participants) and in 1996 (3,626 participants) were included in the analysis. We first compared the distribution of birth characteristics between the two surveys. We then calculated the rate of utilization of various prenatal and intrapartum care services in the two surveys in the overall sample and in subsamples, stratified by maternal education, age, and parity. RESULTS: The utilization of most prenatal and intrapartum care services, especially the complicated laboratory tests, increased in 1996 compared to 1989. For example, the proportion of women who received amniocentesis increased from 1.62% in 1989 to 5.60% in 1996 and German measles testing increased from 5.96% to 27.11%. By contrast, the proportion of women who received consultation services was stable over time, or for family planning, consultation declined from 33.21% to 27.00%. These changes in utilization over time were consistently observed across different maternal education, age, and parity groups. CONCLUSIONS: The utilization of prenatal and intrapartum care services, especially for the more expensive services, has substantially increased in Taiwan since the implementation of the national health insurance. For countries considering similar national health insurance plan, it may be helpful to consider cost-containing measures before the implementation of such a plan.

Adolescent↗

PubMed2001

Maternal asthma and pregnancy outcomes: a retrospective cohort study.

OBJECTIVE: We examined the relationship between asthma during pregnancy and selected infant and maternal outcomes. STUDY DESIGN: A retrospective cohort study was conducted on mother-infant dyads identified from a linked infant and maternal hospital discharge database in the Canadian province of Quebec between fiscal years 1991-1992 and 1995-1996. Mothers with asthma (n = 2193) were compared with a randomly selected control sample (n = 8772) from the remaining population of mothers. RESULTS: After important confounding variables were accounted for, maternal asthma was significantly associated with several adverse infant outcomes, including preterm birth and birth of infants who are very small for gestational age, and adverse maternal outcomes, such as idiopathic preterm labor, early idiopathic preterm labor, preeclampsia, transient hypertension of pregnancy, pregnancy-associated hypertension, chorioamnionitis, and cesarean delivery. CONCLUSION: Our results demonstrated that pregnant women with asthma are at substantially increased risk for several adverse infant and maternal outcomes and suggest the need for extra attention to mothers with asthma and their infants.

Abruptio Placentae↗

PubMed2001

The relationship between cervical dilatation at initial presentation in labour and subsequent intervention.

OBJECTIVE: To examine the relationship between the cervical dilatation at which women present in labour and the subsequent likelihood of caesarean section. DESIGN: Retrospective cohort study. SETTING: University teaching hospital. POPULATION: 3,220 women met the entry criteria from 14,050 deliveries between January 1995 and December 1999. METHODS: Women meeting the following criteria were identified: those in spontaneous labour with a singleton pregnancy and a cephalic presentation at 37-42 weeks of gestation; all women delivering within 36 hours of first presentation were included. Women who had spontaneous rupture of the membranes before first attendance were excluded. MAIN OUTCOME MEASURES: The primary outcome was the rate of caesarean section. Secondary outcomes were operative vaginal delivery, fetal weight, cord pH, five minute Apgar score, length of labour, labour augmentation with oxytocin and epidural analgesia. RESULTS: The risk of caesarean section decreased with increasing cervical dilatation at presentation. This was true for nulliparous (n = 1,168) and parous women (n = 2,052). The caesarean section rate of nulliparous women presenting at 0-3cm (n = 812) was 10.3%, compared with 4.2% for those presenting at 4cm-10 cm (n = 356), and the mean duration of labour before presentation was 2.0 hours versus 4.5 hours, respectively (P = 0.0001). For parous women the caesarean section rates were 5.7% and 1.3%, respectively (P = 0.0001). There were significantly greater frequencies of use of oxytocin and epidural analgesia by women presenting earlier in labour. The caesarean section rate of 185 nulliparae (15.8%) who were initially allowed home was no different from those admitted immediately (9.2% vs 8.2%, P = 0.67). Similarly, 196 (9.5%) of multiparae went home and had a caesarean section rate of 3.6%, compared with 3.1% if admitted immediately (P = 0.76). CONCLUSIONS: Women who present to hospital at 0-3cm spend less time in labour before presentation and are more likely to have obstetric intervention than those presenting in more advanced labour. Outcomes were similar whether or not the woman was initially allowed home.

Adult↗

PubMed2001

Level of aggregation for optimal epidemiological analysis: the case of time to surgery and unnecessary removal of the normal appendix.

STUDY OBJECTIVE: To illustrate the concept of "individualised fallacy", the result of improper interpretation and inference about aggregate level associations on the basis of associations at the individual level, in epidemiology. DESIGN: Cohort study. SETTING: Canadian province of Ontario. PATIENTS: All patients who underwent primary appendicectomy in 175 Ontario hospitals from 1989 to 1992. The association between rate of normal appendix removal and time to surgery was analysed at two levels: (1) at individual patient level, in which, for each patient, the exact number of days to surgery was derived, and (2) at hospital level, in which hospital specific proportions of time to surgery was calculated. MAIN RESULTS: Measured at individual level, compared with patients who had an operation on the same day of admission, the odds ratio was 2.41 (95% confidence intervals 2.28, 2.56) for patients who had an operation > 1 day after admission. Measured at hospital level, each 10% increase in the proportion of patients who had an operation > 1 day after admission resulted in a 15% reduction in the odds of normal appendix removal (odds ratio 0.85, 95% confidence intervals 0.82, 0.88) CONCLUSIONS: In this case study, hospital level measure correctly predicted a reduction in the rate of normal appendix removal by delaying surgery, whereas individual level measure biased the direction of the relation to the opposite. This example illustrates that bias in across level inference can occur either at individual or ecological level. The preferred level of analysis is the one that minimises confounding; often, it must be selected on the basis of a priori knowledge of the subject area.

Adolescent↗

PubMed2001

A new and improved population-based Canadian reference for birth weight for gestational age.

BACKGROUND: Existing fetal growth references all suffer from 1 or more major methodologic problems, including errors in reported gestational age, biologically implausible birth weight for gestational age, insufficient sample sizes at low gestational age, single-hospital or other non-population-based samples, and inadequate statistical modeling techniques. METHODS: We used the newly developed Canadian national linked file of singleton births and infant deaths for births between 1994 and 1996, for which gestational age is largely based on early ultrasound estimates. Assuming a normal distribution for birth weight at each gestational age, we used the expectation-maximization algorithm to exclude infants with gestational ages that were more consistent with 40-week births than with the observed gestational age. Distributions of birth weight at the corrected gestational ages were then statistically smoothed. RESULTS: The resulting male and female curves provide smooth and biologically plausible means, standard deviations, and percentile cutoffs for defining small- and large-for-gestational-age births. Large-for-gestational age cutoffs (90th percentile) at low gestational ages are considerably lower than those of existing references, whereas small-for-gestational-age cutoffs (10th percentile) postterm are higher. For example, compared with the current World Health Organization reference from California (Williams et al, 1982) and a recently proposed US national reference (Alexander et al, 1996), the 90th percentiles for singleton males at 30 weeks are 1837 versus 2159 and 2710 g. The corresponding 10th percentiles at 42 weeks are 3233 versus 3086 and 2998 g. CONCLUSIONS: This new sex-specific, population-based reference should improve clinical assessment of growth in individual newborns, population-based surveillance of geographic and temporal trends in birth weight for gestational age, and evaluation of clinical or public health interventions to enhance fetal growth. fetal growth, birth weight, gestational age, preterm birth, postterm birth.

Algorithms↗

PubMed2001

Changes in stillbirth and infant mortality associated with increases in preterm birth among twins.

OBJECTIVE: To examine whether the recent substantial increase in preterm birth among twins has been associated with changes in fetal and infant mortality. DESIGN: Cohort study based on information in the linked live birth, stillbirth, and mortality databases of Statistics Canada. SETTING: Ten of 12 provinces and territories in Canada. PARTICIPANTS: All twin live births and stillbirths between 1985 and 1996, along with information on deaths during infancy (1985-1997). MAIN OUTCOME MEASURE: Fetal and infant mortality rates. RESULTS: The rate of preterm birth among twin live births increased significantly by 17% (95% confidence interval: 14%-20%) from 42.5% between 1985 and 1987 to 49.6% between 1994 and 1996. Overall, stillbirth rates among twins declined from 22.4 per 1000 total births in 1985 to 1987 to 18.8 per 1000 total births in 1994 to 1996. Among twin fetuses >/=34 weeks' gestation, stillbirth rates decreased from 9.5 per 1000 in 1985 to 1987 to 5.4 per 1000 fetuses at risk in 1994 to 1996. Infant mortality rates among twin live births declined substantially in all categories of gestational age above 24 weeks except for live births at 32 to 33 and 34 to 36 weeks' gestation. CONCLUSIONS: The recent increase in preterm birth among twins was associated with a substantial reduction in stillbirth rates at and near term gestation. Infant mortality rates declined concurrently, although the absence of a significant decrease in infant mortality among twin live births at 32 to 33 and 34 to 36 weeks' gestational age needs additional scrutiny.

Canada↗