Smallpox during pregnancy and maternal outcomes

A historical study evaluated maternal outcomes in pregnancy complicated by smallpox. The overall case fatality was estimated to be 34.3% (95% confidence interval [CI] 31.4-37.1), and the proportion of miscarriage or premature birth was estimated to be 39.9% (95% CI 36.5-43.2). Vaccination before pregnancy reduced the risk for death.     

Linking Birth and Infant Death Records With Assisted Reproductive Technology Data: Massachusetts, 1997–1998

Objectives: To link data from the US assisted reproductive technology (ART) registry with the Massachusetts birth–infant death file to create a comprehensive dataset on the circumstances surrounding conception and maternal and infant outcomes for a population of ART-conceived infants. Methods: The authors sought to link data for 3704 ART-conceived live-born infants from 2703 deliveries in 1997–1998 involving Massachusetts resident mothers who gave birth in Massachusetts, Rhode Island, New Hampshire, or Connecticut to their corresponding Massachusetts birth record using a two-stage algorithm. Maternal and infant dates of birth served as the primary linkage variables. Maternal names for a subset of the ART-conceived infants were obtained and used in the second stage of the algorithm to confirm a sample of records that matched in Stage I, to resolve duplicate matches, and to link unmatched records. Results: In Stage I, 78% of ART deliveries matched with only one Massachusetts record, 2% matched with two records, and 20% remained unmatched. Overall, the complete algorithm using maternal name data for a portion of records yielded an 89% linkage rate. Nearly all of the records that matched during Stage I that were evaluated with maternal name data in Stage II were confirmed as correctly linked. Conclusions: This project confirms that high-yield data linkage can be achieved in the absence of specific identifiers (e.g., name and social security number). Nonetheless, additional matches were achieved when name data were obtained. This linkage creates the first population-based file in the US capturing detailed information on ART births.     

The Temporal Stage fallacy: A novel statistical fallacy in the medical literature

Celebrated for disproving the traditional view that lack of oxygen at birth (perinatal asphyxia) contributes significantly to cerebral palsy, a 1986 New England Journal of Medicine article by Karin Nelson and Jonas Ellenberg engineered a new consensus in the medical community: that lack of oxygen at birth rarely causes cerebral palsy. We demonstrate that the article's central argument relies on straightforwardly fallacious statistical reasoning, and we discuss significant implications -- e.g. how carefully fetuses are monitored during labor and delivery, expert testimony in malpractice cases, and public policy decisions.     

Matching estimates of the impact of over-the-counter emergency birth control on teenage pregnancy

In this paper, we demonstrate how matching estimators can be used to evaluate policy interventions which are implemented in relatively few regions at different times. Our technique is based on translating calendar time into 'experimental time' to provide a common starting point for entry by different areas into the scheme. Such an approach is likely to have many applications, in particular to cases of state- or country-level interventions for which only aggregate data are available. We illustrate the technique using the case of free over-the-counter access to emergency birth control for teenagers at pharmacies in England. We construct matching estimates of the impact of this scheme on the under-18 conception rate in local authorities. Irrespective of either the matching or the adjustment procedure, we find no evidence that over-the-counter emergency birth control schemes lead to lower teenage pregnancy rates.     

Prenatal cigarette smoke exposure: pregnancy outcome and gestational changes in plasma nicotine concentration, hematocrit, and carboxyhemoglobin in a newly standardized rat model

Epidemiological studies support an association between perinatal cigarette smoke (CS) exposure and a number of severe pre- and postnatal complications. However, the mechanisms through which CS enhances such risks largely remain unknown. One of the reasons for our inability to discover such mechanisms has been the unavailability of a clinically relevant and physiologically concordant animal model. A number of studies have previously used nicotine (Nic) as surrogate for CS. We sought to (1) establish the amount of CS exposure to achieve plasma Nic concentrations observed among moderate to heavy smokers (20-60 ng/ml), (2) investigate the temporal changes in plasma Nic concentrations, carboxyhemoglobin, and hematocrit with advancing pregnancy, and (3) elucidate the effects of CS exposure on pregnancy outcome. Pregnant Sprague-Dawley rats were exposed to various doses of CS or room air (Sham) from days 6 to 21 of gestation. Exposure to 6000 ml/day of CS led to very high plasma Nic concentrations and increased maternal and fetal mortality (P < 0.001). The plasma Nic concentrations remained higher than those observed in moderate smokers until the CS dose was reduced to 1000 ml/day and showed dose-dependent temporal changes with advancing gestational age. Significant increases in carboxyhemoglobin and hematocrit were observed in the CS group as compared with the Sham group (P < 0.001). In addition, prenatally CS exposed fetuses had lower birth weight as compared with the Sham group (P = 0.04). Our current study establishes a newly standardized and physiologically relevant model to investigate the mechanisms of CS-mediated adverse effects during the critical period of fetal development.     

Relationships between air pollution and preterm birth in California

Air pollution from vehicular emissions and other combustion sources is related to cardiovascular and respiratory outcomes. However, few studies have investigated the relationship between air pollution and preterm birth, a primary cause of infant mortality and morbidity. This analysis examined the effect of fine particulate matter (PM(2.5)) and carbon monoxide (CO) on preterm birth in a matched case-control study. PM(2.5) and CO monitoring data from the California Air Resources Board were linked to California birth certificate data for singletons born in 1999-2000. Each birth was mapped to the closest PM monitor within 5 miles of the home address. County-level CO measures were utilised to increase sample size and maintain a representative population. After exclusion of implausible birthweight-gestation combinations, preterm birth was defined as birth occurring between 24 and 36 weeks' gestation. Each of the 10 673 preterm cases was matched to three controls of term (39-44 weeks) gestation with a similar date of last menstrual period. Based on the case's gestational age, CO and PM(2.5) exposures were calculated for total pregnancy, first month of pregnancy, and last 2 weeks of pregnancy. Exposures were divided into quartiles; the lowest quartile was the reference. Because of the matched design, conditional logistic regression was used to adjust for maternal race/ethnicity, age, parity, marital status and education. High total pregnancy PM(2.5) exposure was associated with a small effect on preterm birth, after adjustment for maternal factors (adjusted odds ratio [AOR] = 1.15, [95% CI 1.07, 1.24]). The odds ratio did not change after adjustment for CO. Results were similar for PM(2.5) exposure during the first month of pregnancy (AOR = 1.21, 95% CI [1.12, 1.30]) and the last 2 weeks of pregnancy (AOR = 1.17, 95% CI [1.09, 1.27]). Conversely, CO exposure at any time during pregnancy was not associated with preterm birth (AORs from 0.95 to 1.00). Maternal exposure to PM(2.5), but not CO, is associated with preterm birth. This analysis did not show differences by timing of exposure, although more detailed examination may be needed.     

Characteristics of unmatched maternal and baby records in linked birth records and hospital discharge data

Linkage of routinely collected health data collections is increasingly being used to investigate maternal and infant morbidity and mortality. Such data have the advantage of being population based and readily available. However, in using such data it is important to understand the data linkage process, the proportions of unmatched records and the characteristics of these records so that potential bias can be recognised. This article describes the differences in characteristics of matched and unmatched mothers' and babies' records generated in the linkage of birth records with hospital discharge data and explores some of the reasons for these differences. The study population included over 250,000 women and their babies discharged from hospital following delivery in New South Wales, Australia between 1 January 2000 and 31 December 2002. Hospital discharge and birth data were linked using probabilistic linkage methods for both mothers and babies. Matching rates were 98.5% and 99.0% for maternal birth and hospital discharge records, respectively, and 98.8% and 99.4% for baby records. Unmatched maternal records had higher proportions of Australian-born women, private hospital births and stillbirths compared with matched records. Unmatched baby records had higher proportions of low-birthweight babies, preterm births and in-hospital deaths than matched records. With the possible exception of stillbirths, these differences are unlikely to cause important bias in studies relying on matched records only. Our results suggest studies using linked data should generally examine and report on the characteristics of unmatched records, and recognise them as a potential source of bias.     

Short birth intervals and the risk of school unreadiness among a Medicaid population in South Carolina

BACKGROUND: Communities across the United States have become more involved in enhancing school readiness. Many of the predictors of school readiness relate to conditions prior to and following the birth of the child, including a child's birthweight. Shortened birth intervals are related to a variety of health and social consequences that affect child development, yet no formal research has examined the association between birth intervals and school readiness. METHODS: This study was a secondary data analysis of de-identified pregnancy-related vital record information, matched to selected items from the Department of Health and Human Services Medicaid records on mothers and children and to the Cognitive Skills Assessment Battery score in South Carolina for the year 2000 for the child of interest (N = 6915). Analysis of covariance and logistic regression were used to determine if there was a statistically significant relationship between birth interval and school readiness. RESULTS: Results showed that birth interval is a significant predictor of school readiness with a P-value <0.001 even after controlling for various socio-demographic factors. Children born with inadequate birth intervals (less than 24 months) are more likely to fail the Cognitive Skills Assessment Battery compared with those with adequate birth intervals. Potential implications of this research include promoting optimal birth spacing to improve the likelihood that future first graders will come to school ready to learn.     

A flow sensor suitable for use with split-flow ventilation--first preclinical data

Volutrauma caused by artificial ventilation represents a major morbidity risk for premature infants. Our working group has recently developed an innovative "split-flow ventilation" system aiming at the reduction of tidal volumes (TVs). The main problem for the practical use of this system is the fact that conventional measurements of commercially available flow sensors are distorted by the split flow. In this study, we present the first preclinical data from testing an adapted flow sensor combination recognizing the split flow. A preterm infant test lung was conventionally ventilated, modified by insertion of a split-flow line. In addition to the customary flow sensor (FS-1), a second flow sensor (FS-2) was integrated into the split-flow line, and a third (FS-3) was placed at the exit of the test lung for reference measurements. The signals of all three flow sensors were read and processed by a computer. The program was set to graphically add up flow curves 1, 2, and 3 during one ventilation loop. After 10 runs, a mean curve of FS-1+2 was calculated and compared to the mean curve of FS-3. Furthermore, the mean TV of 10 runs measured by FS-1+2 was calculated and compared with the mean TV calculated by FS-3. The summation curve FS-1+2 proved identical to the reference curve FS-3. FS-1+2 yielded a TV of 6.6 +/- 0.01 mL (inspiratory) and 6.7 +/- 0.02 mL (expiratory). The corresponding values of FS-3 were 6.5 +/- 0.20 mL and 6.6 +/- 0.09 mL, respectively. According to our results, the presented flow sensor constellation allows exact flow measurements in the experimental setting and appears suitable for usage in a split-flow ventilation circuit under clinical conditions.     

Surgical necrotizing enterocolitis and intraventricular hemorrhage in premature infants below 1000 g

Background/Purpose

Infants with very low birth weight are at increased risk for both intraventricular hemorrhage (IVH) and necrotizing enterocolitis (NEC). IVH often progresses in severity after initial diagnosis and causes severe neurological morbidity and mortality. The authors examined the role of NEC in the progression of IVH in these infants.

Methods

The authors conducted a retrospective case-control study using data from the University of Maryland neonatal intensive care unit database between 1991 and 2003. From a cohort of 957 infants with very low birth weight, 53 pairs of infants labeled as IVH progression versus controls were selected and closely matched in respect to their gestational age and birth weight. Charts from these infants were reviewed to identify risk factors contributing to IVH progression.

Results

Infants with IVH progression were significantly more likely to suffer from NEC (odds ratio, 3.6), whereas infants with surgical NEC showed a greater association with IVH progression (odds ratio, 5.33). Association with thrombocytopenia was also seen (odds ratio, 3.33). Sepsis showed trend toward significance (odds ratio, 1.9; P = .095) for progression of IVH.

Conclusion

Surgical NEC showed the greatest risk for IVH progression. NEC and thrombocytopenia also appear to be risk factors for IVH progression.