Linda Dodds

Impact of influenza exposure on rates of hospital admissions and physician visits because of respiratory illness among pregnant women

Background: Excess deaths have occurred among pregnant women during influenza pandemics, but the impact of influenza during nonpandemic years is unclear. We evaluated the impact of exposure during nonpandemic influenza seasons on the rates of hospital admissions and physician visits because of respiratory illness among pregnant women. Methods: We conducted a 13-year (1990–2002) population-based cohort study involving pregnant women in Nova Scotia. We compared rates of hospital admissions and physician office visits because of respiratory illness during the influenza season in each trimester of pregnancy with rates during the influenza season in the year before pregnancy and with rates in non-influenza seasons. Poisson regression analyses were performed to estimate rate ratios and 95% confidence intervals (CIs). Results: Of 134 188 pregnant women in the study cohort, 510 (0.4%) were admitted to hospital because of a respiratory illness during pregnancy and 33 775 (25.2%) visited their physician for the same reason during pregnancy. During the influenza seasons, the rate ratio of hospital admissions in the third trimester compared with admissions in the year before pregnancy was 7.9 (95% CI 5.0–12.5) among women with comorbidities and 5.1 (95% CI 3.6–7.3) among those without comorbidities. The rate of hospital admissions in the third trimester among women without comorbidities was 7.4 per 10 000 woman-months during the influenza season, compared with 5.4 and 3.1 per 10 000 woman-months during the peri-and non-influenza seasons respectively. Corresponding rates among women with comorbidities were 44.9, 9.3 and 18.9 per 10 000 woman-months. Only 6.7% of women with comorbidities had received influenza immunization. Interpretation: Our data support the recommendation that pregnant women with comorbidities should receive influenza vaccination regardless of their stage of pregnancy during the influenza season. Since hospital admissions because of respiratory illness during the influenza season were also increased among pregnant women without comorbidities, all pregnant women are likely to benefit from influenza vaccination.

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

Risk factors for renal cell carcinoma: results of a population-based case-control study

For a case-control study of risk factors for renal cell carcinoma, a mailed questionnaire was used to collect data on 518 cases and 1,381 population-based controls in Ontario, Canada. Active cigarette smoking increased risk twofold among males (odds ratio estimate [OR]=2.0, 95 percent confidence interval (CI)=1.4–2.8) and females (OR=1.9, CI=1.3–2.6). Passive smoking appeared to increase risk somewhat among nonsmokers (males: OR=1.6, CI=0.5–4.7; females: OR=1.7, CI=0.8–3.4). A high Quetelet index (QI) was associated with a twofold increase in risk in both sexes, although this was based on reported weight at age 25 years for males (OR=1.9, CI=1.2–3.1) and five years prior to data collection for females (OR=2.5, CI=1.4–4.6). Diuretic use was associated with significantly increased risk among females, but not among males. Phenacetin use increased risk, while acetaminophen use was not associated with altered risk, although few subjects used either compound. Multiple urinary tract infections increased risk, but only significantly in females (OR=1.9, CI=1.2–2.9). Our data indicate the need for further exploration of passive smoking and diuretics as risk factors, as well as elucidation of mechanisms by which high lifetime QI and frequent urinary-tract infections might increase risk of this cancer.

Trihalomethanes in public water supplies and adverse birth outcomes.

We conducted a retrospective cohort study to evaluate the relation between the level of total trihalomethanes in drinking water and adverse birth outcomes. The study population comprised women residing in an area with municipal surface water who had a singleton birth in Nova Scotia between January 1, 1988, and December 31, 1995, or a pregnancy termination for a major fetal anomaly. We found little association between trihalomethane level and the outcomes related to fetal weight or gestational age, but we found an elevated relative risk for stillbirths for average trihalomethane levels during pregnancy of 100 microg/liter or greater (adjusted relative risk = 1.66; 95% confidence interval = 1.09-2.52) relative to women exposed to trihalomethane levels of 0-49 microg/liter. We saw little evidence of an elevated prevalence or dose-response pattern for congenital anomalies, with the possible exception of chromosomal abnormalities (adjusted prevalence ratio = 1.38 and 95% confidence interval = 0.73-2.59 for women exposed to trihalomethane levels of 100 microg/liter or greater).

Outcomes of pregnancies complicated by hyperemesis gravidarum.

OBJECTIVE: To evaluate maternal and neonatal outcomes among women with hyperemesis during pregnancy. METHODS: A population-based retrospective cohort study was conducted among women with singleton deliveries between 1988 and 2002. Hyperemetic pregnancies were defined as those requiring one or more antepartum admissions for hyperemesis before 24 weeks of gestation. Severity of hyperemesis was evaluated according to the number of antenatal hospital admissions (1 or 2 versus 3 or more) and according to weight gain during pregnancy (< 7 kg [15.4 lb] versus ≥ 7 kg). Maternal outcomes evaluated included weight gain during pregnancy, gestational diabetes, gestational hypertension, labor induction, and cesarean delivery. Neonatal outcomes included 5-minute Apgar score of less than 7, low birth weight, small for gestational age, preterm delivery, and perinatal death. Logistic regression was used to generate adjusted odds ratios for all outcomes, and the odds ratios were converted to relative risks. RESULTS: Of the 156,091 singleton pregnancies, 1,270 had an admission for hyperemesis. Compared to women without hyperemesis, infants born to women with hyperemesis and with low pregnancy weight gain (< 7 kg [15.4 lb]) were more likely to be low birth weight, small for gestational age (SGA), born before 37 weeks of gestation, and have a 5-minute Apgar score of less than 7. Compared with infants born to women without hyperemesis, rates of low birth weight and preterm delivery were substantially higher among infants born to women with hyperemesis and low pregnancy weight gain (4.2% versus 12.5% and 4.9% versus 13.9%, respectively). The outcomes among infants born to women with hyperemesis with pregnancy weight gain of 7 kg (15.4 lb) or more were not different from the outcomes among women without hyperemesis. CONCLUSION: The results of this study suggest that the adverse infant outcomes associated with hyperemesis are a consequence of, and mostly limited to, women with poor maternal weight gain. LEVEL OF EVIDENCE: II-2

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.

Perinatal outcomes in women with asthma during pregnancy

Objective To determine whether adverse perinatal outcome is associated with asthma or asthma medication use during pregnancy. Methods A retrospective cohort study was conducted of women who resided in Halifax County, Nova Scotia, and delivered between 1991 and 1993. Asthmatic women were classified into three groups, according to medication usage: no medications, beta agonists only, and steroids with or without other asthma medications. Outcomes compared among asthmatic and nonasthmatic women included maternal complications (pregnancy-induced hypertension, cesarean delivery, gestational diabetes, preterm birth, and antepartum and postpartum hemorrhage) and neonatal outcomes (low birth weight, congenital malformations, hyperbilirubinemia, and respiratory distress syndrome). Results The cohort included 817 asthmatic women and 13,709 nonasthmatic women. Overall, the prevalence of pregnancies complicated by asthma increased from 4.8% in 1991 to 6.9% in 1993. Asthmatic women were at increased risk for antepartum and postpartum hemorrhage, independent of medication usage. Asthmatic women taking steroids were at increased risk for pregnancy-induced hypertension (odds ratio [OR] 1.7; 95% confidence interval [CI] 1.0, 2.9). The only significant difference in neonatal outcome between asthma medication groups and nonasthmatic women was of an increased risk of hyperbilirubinemia in infants of women taking steroids (OR 1.9; 95% CI 1.1, 3.4). Conclusion Risk of antepartum and postpartum hemorrhage is increased in asthmatic women, independent of medication usage. The increased incidence of neonatal hyperbilirubinemia and the borderline increased risk of pregnancy-induced hypertension may be complications of steroid use or may be related to poorly controlled asthma.

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.

Risk factors for hyperemesis gravidarum requiring hospital admission during pregnancy.

OBJECTIVE: To identify risk factors for hyperemesis requiring hospital admission during pregnancy. METHODS: Data from a population-based cohort of all deliveries in Nova Scotia, Canada between 1988 and 2002 were obtained from the Nova Scotia Atlee Perinatal Database. Women with 1 or more antepartum admissions for hyperemesis were compared with women with no admissions for hyperemesis. Relative risks (RRs) and 95% confidence intervals (CIs) were estimated using logistic regression and used to determine a set of independent risk factors for hyperemesis. RESULTS: The overall rate of admission for hyperemesis was 0.8% (n = 1,301) among 157,922 deliveries. In the adjusted analysis, hyperthyroid disorders (RR 4.5, 95% CI 1.8–11.1), psychiatric illness (RR 4.1, 95% CI 3.0–5.7), previous molar pregnancy (RR 3.3, 95% CI 1.6–6.8), preexisting diabetes (RR 2.6, 95% CI 1.5–4.7), gastrointestinal disorders (RR 2.5, 95% CI 1.8–3.6), and asthma (RR 1.5, 95% CI 1.2–1.9) were all statistically significant risk factors for hyperemesis, whereas maternal smoking and maternal age older than 30 were associated with decreased risk. Compared with singleton male pregnancies, singleton female pregnancies, pregnancies with multiple male fetuses, and male and female combinations were associated with statistically significant increased risk of hyperemesis. CONCLUSION: Although hospitalization for hyperemesis occurs in less than 1% of pregnant women, this translates to a large number of hospital admissions. The factors associated with hyperemesis are primarily medical and fetal factors that are not easily modifiable, but identification of these factors may be useful in determining those women at high risk for developing hyperemesis. LEVEL OF EVIDENCE: II-2

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.