Alexander C. Allen

Epidemic Listeriosis — Evidence for Transmission by Food

The bacterium Listeria monocytogenes is a motile, gram-positive coccobacillus that can frequently be isolated from soil, water, and vegetation. It is a common cause of meningoencephalitis and abort...

Determinants of Preterm Birth Rates in Canada from 1981 through 1983 and from 1992 through 1994

BACKGROUND The rates of preterm birth have increased in many countries, including Canada, over the past 20 years. However, the factors underlying the increase are poorly understood. METHODS We used data from the Statistics Canada live-birth and stillbirth data bases to determine the effects of changes in the frequency of multiple births, registration of births occurring very early in gestation, patterns of obstetrical intervention, and use of ultrasonographic dating of gestational age on the rates of preterm birth in Canada from 1981 through 1983 and from 1992 through 1994. All births in 9 of the 12 provinces and territories of Canada were included. Logistic-regression analysis and Poisson regression analysis were used to estimate changes between the two three-year periods, after adjustment for the above-mentioned determinants of the likelihood of preterm births. RESULTS Preterm births increased from 6.3 percent of live births in 1981 through 1983 to 6.8 percent in 1992 through 1994, a relative increase of 9 percent (95 percent confidence interval, 7 to 10 percent). Among singleton births, preterm births increased by 5 percent (95 percent confidence interval, 3 to 6 percent). Multiple births increased from 1.9 percent to 2.1 percent of all live births; the rates of preterm birth among live births resulting from multiple gestations increased by 25 percent (95 percent confidence interval, 21 to 28 percent). Adjustment for the determinants of the likelihood of preterm birth reduced the increase in the rate of preterm birth to 3 percent among all live births and 1 percent among singleton births. CONCLUSIONS The recent increase in preterm births in Canada is largely attributable to changes in the frequency of multiple births, obstetrical intervention, and the use of ultrasound-based estimates of gestational age.

The perinatal effects of delayed childbearing.

OBJECTIVE: To determine if the rates of pregnancy complications, preterm birth, small for gestational age, perinatal mortality, and serious neonatal morbidity are higher among mothers aged 35–39 years or 40 years or older, compared with mothers 20–24 years. METHODS: We performed a population-based study of all women in Nova Scotia, Canada, who delivered a singleton fetus between 1988 and 2002 (N = 157,445). Family income of women who delivered between 1988 and 1995 was obtained through a confidential linkage with tax records (n = 76,300). The primary outcome was perinatal death (excluding congenital anomalies) or serious neonatal morbidity. Analysis was based on logistic models. RESULTS: Older women were more likely to be married, affluent, weigh 70 kg or more, attend prenatal classes, and have a bad obstetric history but less likely to be nulliparous and to smoke. They were more likely to have hypertension, diabetes mellitus, placental abruption, or placenta previa. Preterm birth and small-for-gestational age rates were also higher; compared with women aged 20–24 years, adjusted rate ratios for preterm birth among women aged 35–39 years and 40 years or older were 1.61 (95% confidence interval [CI] 1.42–1.82; P < .001) and 1.80 (95% CI 1.37–2.36; P < .001), respectively. Adjusted rate ratios for perinatal mortality/morbidity were 1.46 (95% CI 1.11–1.92; P = .007) among women 35–39 years and 1.95 (95% CI 1.13–3.35; P = .02) among women 40 years or older. Perinatal mortality rates were low at all ages, especially in recent years. CONCLUSION: Older maternal age is associated with relatively higher risks of perinatal mortality/morbidity, although the absolute rate of such outcomes is low. LEVEL OF EVIDENCE: II-2

Increasing Prevalence of Cerebral Palsy Among Very Preterm Infants: A Population-Based Study

OBJECTIVES. It is unclear whether declines in neonatal and infant mortality have led to changes in the occurrence of cerebral palsy. We conducted a study to examine and investigate recent temporal changes in the prevalence of cerebral palsy in a population-based cohort of very preterm infants who were 24 to 30 weeks of gestational age. METHODS. A population-based cohort of very preterm infants who were born between January 1, 1993, and December 31, 2002, was evaluated by the Perinatal Follow-up Program of Nova Scotia. Follow-up extended to age 2 years to ascertain the presence or absence of cerebral palsy and for overall survival. Infant survival and cerebral palsy rates were compared by year and also in two 5-year periods, 1993–1997 and 1998–2002. Logistic regression analyses were used to identify factors that potentially were responsible for temporal changes in cerebral palsy rates. RESULTS. A total of 672 liveborn very preterm infants were born to mothers who resided in Nova Scotia between 1993 and 2002. Infant mortality among very preterm infants decreased from 256 per 1000 live births in 1993 to 114 per 1000 live births in 2002, whereas the cerebral palsy rates increased from 44.4 per 1000 live births in 1993 to 100.0 per 1000 live births in 2002. Low gestational age, postnatal dexamethasone use, patent ductus arteriosus, severe hyaline membrane disease, resuscitation in the delivery room, and intraventricular hemorrhage were associated with higher rates of cerebral palsy, whereas antenatal corticosteroid use was associated with a lower rate. CONCLUSION. Cerebral palsy has increased substantially among very preterm infants in association with and possibly as a consequence of large declines in infant mortality.

Perinatal implications of shoulder dystocia

Objective To assess the antecedents of shoulder dystocia, the risk of recurrence, and the perinatal morbidity associated with the different maneuvers used for its management. Methods We conducted a 10-year (1980–1989) retrospective case record review of all instances of shoulder dystocia in a teaching maternity hospital. Results There were 254 cases of shoulder dystocia in 40,518 vaginal cephalic deliveries (0.6%), with 33 cases (13.0%) of brachial plexus palsy and 13 fractures (5.1%). There were no perinatal deaths attributable to shoulder dystocia. The risk of shoulder dystocia was increased with prolonged pregnancy (threefold), prolonged second stage of labor (threefold), mid-forceps deliveries (tenfold), and increasing birth weight. Of the maneuvers used to deal with shoulder dystocia, strong downward traction on the head was significantly correlated with brachial plexus palsy compared with other individual methods of delivering the shoulders. There was only one case of recurrent shoulder dystocia in 80 women having 93 cephalic vaginal deliveries after their original delivery coded with shoulder dystocia. Conclusion Shoulder dystocia is not a reliably predictable event in labor. Although the risk of shoulder dystocia is increased with prolonged pregnancy, prolonged second stage of labor, increasing birth weight, and mid-forceps delivery, the majority of cases occur without these risk factors. Strong downward traction on the head is associated with the greatest degree of neonatal trauma, whereas McRoberts maneuver has the least. The risk of recurrent shoulder dystocia is low.

Risk of respiratory distress syndrome related to gestational age, route of delivery, and maternal diabetes.

Abstract From this analysis, respiratory distress syndrome appears to be a condition related to prematurity, exacerbated by cesarean section delivery, and unaffected by maternal diabetes. The incidence and mortality rate are inversely related to gestational age with the syndrome probably rarely, if ever, occurring after 38 weeks. Cesarean section is associated with a markedly increased incidence and mortality rate. The incidence of respiratory distress syndrome in infants of diabetic mothers is the same as in infants of nondiabetic mothers when delivered at the same gestational age and by the same route. When premature delivery is considered for maternal or fetal complications, it should, whenever possible, be effected vaginally rather than by cesarean section.

Changes in maternal characteristics and obstetric practice and recent increases in primary cesarean delivery.

OBJECTIVE To estimate the contribution of changes in maternal characteristics (namely, age, parity, prepregnancy weight, weight gain in pregnancy, smoking status) and obstetric practice (namely, labor induction, epidural anesthesia, delivery by an obstetrician, midpelvic forceps delivery) to recent increases in primary cesarean delivery rates. METHODS We studied all deliveries in Nova Scotia, Canada, between 1988 and 2000 after excluding women who had a previous cesarean delivery (n = 127,564). Logistic regression was used to study the effect of changes in maternal characteristics and obstetric practice on primary cesarean delivery rates. The effect of changes in midpelvic forceps delivery was examined through ecologic Poisson regression. RESULTS Primary cesarean delivery rates increased from 13.4% of deliveries in 1988 to 17.5% in 2000. This was due to increases in cesarean deliveries for dystocia (14% increase), breech (24% increase), suspected fetal distress (21% increase), hypertension (47% increase), and miscellaneous indications (73% increase). Adjustment for maternal characteristics reduced the temporal increase in primary cesarean delivery rates between 1988-1991 and 1998-2000 from 21% (95% confidence interval [CI] 16%, 25%) to 2% (95% CI -2%, 7%). Additional adjustment for obstetric practice factors further reduced period effects. Midpelvic forceps delivery was significantly and negatively associated with primary cesarean delivery (P =.001). CONCLUSION Recent increases in primary cesarean delivery rates are a consequence of changes in maternal characteristics. Obstetric practice, which has altered due to changes in maternal characteristics and concerns related to fetal and maternal safety, has also contributed to increases in primary cesarean delivery.

A Randomized Trial of Planned Cesarean or Vaginal Delivery for Twin Pregnancy

BACKGROUND Twin birth is associated with a higher risk of adverse perinatal outcomes than singleton birth. It is unclear whether planned cesarean section results in a lower risk of adverse outcomes than planned vaginal delivery in twin pregnancy. METHODS We randomly assigned women between 32 weeks 0 days and 38 weeks 6 days of gestation with twin pregnancy and with the first twin in the cephalic presentation to planned cesarean section or planned vaginal delivery with cesarean only if indicated. Elective delivery was planned between 37 weeks 5 days and 38 weeks 6 days of gestation. The primary outcome was a composite of fetal or neonatal death or serious neonatal morbidity, with the fetus or infant as the unit of analysis for the statistical comparison. RESULTS A total of 1398 women (2795 fetuses) were randomly assigned to planned cesarean delivery and 1406 women (2812 fetuses) to planned vaginal delivery. The rate of cesarean delivery was 90.7% in the planned-cesarean-delivery group and 43.8% in the planned-vaginal-delivery group. Women in the planned-cesarean-delivery group delivered earlier than did those in the planned-vaginal-delivery group (mean number of days from randomization to delivery, 12.4 vs. 13.3; P=0.04). There was no significant difference in the composite primary outcome between the planned-cesarean-delivery group and the planned-vaginal-delivery group (2.2% and 1.9%, respectively; odds ratio with planned cesarean delivery, 1.16; 95% confidence interval, 0.77 to 1.74; P=0.49). CONCLUSIONS In twin pregnancy between 32 weeks 0 days and 38 weeks 6 days of gestation, with the first twin in the cephalic presentation, planned cesarean delivery did not significantly decrease or increase the risk of fetal or neonatal death or serious neonatal morbidity, as compared with planned vaginal delivery. (Funded by the Canadian Institutes of Health Research; ClinicalTrials.gov number, NCT00187369; Current Controlled Trials number, ISRCTN74420086.).

The role of prenatal, obstetric and neonatal factors in the development of autism.

We conducted a linked database cohort study of infants born between 1990 and 2002 in Nova Scotia, Canada. Diagnoses of autism were identified from administrative databases with relevant diagnostic information to 2005. A factor representing genetic susceptibility was defined as having an affected sibling or a mother with a history of a psychiatric or neurologic condition. Among 129,733 children, there were 924 children with an autism diagnosis. The results suggest that among those with low genetic susceptibility, some maternal and obstetric factors may have an independent role in autism etiology whereas among genetically susceptible children, these factors appear to play a lesser role. The role of pre-pregnancy obesity and excessive weight gain during pregnancy on autism risk require further investigation.

Socioeconomic status and perinatal outcomes in a setting with universal access to essential health care services

Background: The health care system in Canada provides essential health services to all women irrespective of socioeconomic status. Our objective was to determine whether perinatal and infant outcomes varied by family income and other socioeconomic factors in this setting. Methods: We included all 92 914 women who delivered in Nova Scotia between 1988 and 1995 following a singleton pregnancy. Family income was obtained for 76 440 of these women through a confidential link to income tax records and was divided into 5 groups. Outcomes studied included pregnancy complications, preterm birth, small-for-gestational-age live birth, perinatal death, serious neonatal morbidity, postneonatal death and infant death. Logistic regression models were used to adjust for potential confounders. Results: Compared with women in the highest family income group, those in the lowest income group had significantly higher rates of gestational diabetes (crude rate ratio [RR] 1.44, 95% confidence interval [CI] 1.21–1.73), preterm birth (crude RR 1.20, 95% CI 1.06–1.35), small-for-gestational-age live birth (crude RR 1.81, 95% CI 1.66–1.97) and postneonatal death (crude RR 5.54, 95% CI 2.21–13.9). The opposite was true for rates of perinatal death (crude RR 0.74, 95% CI 0.56–0.96), and there was no significant difference between the 2 groups in the composite of perinatal death or serious neonatal morbidity (crude RR 1.01, 95% CI 0.82–1.24). Adjustment for behavioural and lifestyle factors accentuated or attenuated socioeconomic differences. Interpretation: Lower family income is associated with increased rates of gestational diabetes, small-for-gestational-age live birth and postneonatal death despite health care services being widely available at no out-of-pocket expense.