Reinterpreting the effects of maternal smoking on infant birthweight and perinatal mortality: a multivariate approach to birthweight standardization.

Infants of women who smoke during pregnancy have lower birthweights and have been observed to have higher rates of perinatal mortality than infants of non-smokers. It is not clear whether this increased risk of mortality is due to an excess of small births among smokers or to an independent effect of smoking. Although infants of smokers have overall higher mortality rates than non-smokers, low birthweight (< 2500 g) infants of smokers have lower mortality rates than low birthweight infants of non-smokers. However, comparison of birthweight-specific mortality between two groups is problematic when there are differences in the birthweight distributions. Methods that have been developed to standardize for these differences by comparing mortality rates relative to their own mean do not allow for simultaneous control of confounding variables. Using data from over 13,000 births of women who participated in a prepaid health care plan we present a method to standardize for birthweight while adjusting for variables that may confound the relationship between maternal smoking and perinatal mortality. After controlling for race, maternal age, education, parity, and number of cigarettes smoked, we found that 85% of the increased mortality due to smoking was attributable to an excess of small births in the birthweight distribution of offspring of smoking mothers, while 15% was due to higher birthweight-specific mortality at almost all standardized birthweights. Contrary to previous reports, we found that low birthweight infants of smoking mothers are at higher risk of perinatal mortality if a population-specific standard for birthweight is used.     

The use of birthweight and gestation to assess perinatal mortality risk.

Using extensive international data it is shown in detail how mortality is related to birthweight and gestation. It is demonstrated that the widely used 'birthweight for length of gestation' standards can be seriously misleading. A new 'high risk' classification is proposed.     

The role of the Maternal and Child Health Handbook system in reducing perinatal mortality in Japan

OBJECTIVE: The purpose of this paper is to demonstrate the direct and indirect roles of the Maternal and Child Health (MCH) Handbook in promoting overall improvement in maternal health and child care and to attempt to clarify the relationship between the use of the MCH Handbook and the reduced perinatal mortality in Japan. Another important objective is to propose possible future applications of the MCH Handbook, especially with respect to the networking function of providing client-care provider feedback, and the exchange of health data between the authorities and relevant medical societies. RESULTS: Japan has achieved a decline in neonatal mortality in the 30-year period from 1960 to 1990, from 17.0 to 2.6 per 1,000 live births. There is a correlation between the ratio of the number of Handbooks distributed and the actual number of births and the perinatal mortality. CONCLUSIONS: The wide use of the MCH Handbook system seems to have played an important role in bringing about this reduction and in maintaining the figure as one of the lowest in the world. The reduction of perinatal mortality through the use of the MCH Handbook in this country suggests a similar possibility for application in other nations. The Handbook could aid in the early recognition of high-risk pregnancy and thus reduce inappropriate use of medical resources. The system, with the establishment of a feedback system between the client and the authorities via the care provider, may improve health care in such areas as maternal mortality, toxemia of pregnancy, and diabetes mellitus.     

Trends and variations in perinatal mortality and low birthweight: the contribution of socio-economic factors

OBJECTIVE: To examine trends and regional variations in perinatal mortality and low birthweight (LBW) and regional variations in socio-economic risk factors. METHODS: Population-based study of Central West Region of Ontario with approximately 28,000 births annually during the period 1988-1995 using vital statistics records and Census data. RESULTS AND CONCLUSIONS: There was no significant change in the perinatal mortality rate averaging 9.4 per 1,000 births per year. The LBW rate increased from 49.7 to 54.8 per 1,000, while the prematurity rate increased from 56.1 to 75.8 per 1,000. Significant variation occurred in outcomes among different regions, which was partially explained by socio-economic factors. The increases in LBW and prematurity rate emphasize the need for effective targeted services and programs. In their planning and implementation, regional variations in socio-economic factors, and other factors such as: the availability and utilization of services and barriers to access in services, require further evaluation and consideration.     

Maternal education as a modifier of the association between low birthweight and infant mortality

Both low birthweight (LBW) and infant mortality rate (IMR) have been consistently shown to be associated with maternal level of educational attainment. This paper examines the mortality risk attributable to LBW in different levels of maternal education. Comprising the study population were 18,715 singleton live births to Jewish mothers ages 20-39, during the years 1977-1980 in the Negev (the southern part of Israel). Data were obtained from a linked record of birth and death certificates. As expected, proportions of LBW (less than 2500 grams) were inversely related to level of maternal education (12.2% in the lowest educational level, 7.9% and 8.0% in the two intermediate levels, and 7.2% in the highest educational level). The mortality risk attributed to LBW was found to be modified by maternal level of education. Mortality ratios standardized for maternal age and parity were computed, using educational level 3, where the lowest mortality rates were observed, as the standard population. Among LBW infants no significant differences were found across educational levels, except for the lowest educational level where only 69% of the expected number of deaths were observed. The survival advantage of LBW infants in the lowest educational level was observed both in the neonatal and the postneonatal periods. Among normal birthweight (NBW) infants, a statistically significant excess mortality was detected both in the highest and the lowest educational levels. The excess mortality of NBW infants in the highest level of maternal education was due to neonatal mortality (SMR = 2.2), while the excess mortality in this birthweight category in the lowest educational level occur mainly in the postneonatal period (SMR = 2.4).(ABSTRACT TRUNCATED AT 250 WORDS)     

Mother''s and father''s birthweight as predictors of infant birthweight

Mothers' and fathers' birthweights are each significantly related to their infants' birthweight, even after control for 31 potentially confounding variables. The relationship is stronger for mothers and daughters than for other parent-offspring pairs. Parents' birthweights together account for 2% of the variance in sons', and 5% of the variance in daughters' birthweights. There are interactions of maternal birthweight with maternal adult weight, pregnancy weight gain, and parity; the predicted effect of maternal birthweight on infant birthweight is enhanced when the mother weighs more, gains more weight during pregnancy, or is multiparous. Race and parents' drinking and smoking also modify the predicted effect of parents' birthweights. The correlation between mother and offspring birthweights has been attributed to the mother's own uterine experience and its effect on her later reproductive performance. However, the significant relationship of father and infant birthweights reported in this paper suggests that the fetal genes also play some role in determining size at birth.     

Racial and ethnic differences in perinatal mortality: the role of fetal death

PURPOSE: We investigate whether variations in infant mortality rates among racial/ethnic groups could be explained by variations in fetal mortality rates where relatively higher infant mortality rates may correspond to lower fetal mortality rates due to possible systematic differences in reporting of fetal death compared to live births. METHODS: Using US perinatal data from 1995 to 1999, we calculated crude mortality rates, birth weight-specific fetal and hebdomadal mortality rates, risks of perinatal death, and the risk of being classified as a fetal death versus other period death among infants born to Non-Hispanic White, Non-Hispanic Black, and Hispanic mothers. RESULTS: Two-fold disparities between Whites and Blacks persist for all mortality categories. Black low birth-weight deliveries, compared to Whites, have perinatal advantages in both fetal and hebdomadal periods. Hispanics were less likely than Whites to be reported as a fetal versus a hebdomadal death. CONCLUSIONS: While these data suggest some underreporting of Black fetal deaths, they provide little evidence that Black-White disparities in infant mortality are a function of variations in classifying a death occurring at delivery as either a fetal death or as a live birth-infant death. These data suggest that the lack of a White-Hispanic disparity in fetal mortality rates may be influenced by underreporting.     

Maternal endometrial oedema may increase perinatal mortality of cloned and transgenic piglets

The perinatal mortality of cloned animals is a well-known problem. In the present retrospective study, we report on mortality of cloned transgenic or non-transgenic piglets produced as part of several investigations. Large White (LW) sows (n = 105) received hand-made cloned LW or minipig blastocysts and delivered either spontaneously or after prostaglandin induction followed by either Caesarean section or vaginal birth. The overall pregnancy rate was 62%, with 26% of pregnancies terminating before term. This resulted in 48 deliveries. The terminated pregnancies consisted of 12 abortions that occurred at 35 ± 2 days gestation and five sows that went to term without returning to heat and then by surgery showed the uterus without fetal content. The gestation length was for sows with LW piglets that delivered by Caesarean section or vaginally was 115.7 ± 0.3 and 117.6 ± 0.4 days, respectively. In sows with minipiglets, the gestation length for those delivered by Caesarean section or vaginally 114.4 ± 0.2 and 115.5 ± 0.3 days, respectively. Of the 34 sows that delivered vaginally, 28 gave birth after induction, whereas 6 farrowed spontaneously. Of the 14 sows that delivered after Caesarean section and in the five empty sows, the endometrium and placenta showed severe oedema. Piglet mortality following vaginal delivery was higher than after Caesarean section (31% v. 10%, respectively; P < 0.001). When vaginal delivery occurred spontaneously, the stillborn rate was greater than after induced delivery (56% v. 24%, respectively; P < 0.0001). Internal organ weights were recorded for seven cloned LW piglets and six normal piglets. The relative weight of the heart, liver, kidneys and small intestine was found to be reduced in the cloned piglets (P < 0.05). The present study demonstrates extensive endometrial oedema in sows pregnant with cloned and transgenic piglets, as well as in empty recipients, at term. The growth of certain organs in some of the cloned piglets was reduced and the rate of stillborn piglets was greater in cloned and transgenic piglets delivered vaginally, possibly because of oedema of the fetal-maternal interface.     

Maternal smoking and low birthweight: implications for antenatal care.

The incidence of low birthweight has been related to smoking prevalence in each social group using published data for 1984. The attributable risk of low birthweight has been estimated, based on a relative risk of 2 for mothers who smoke during pregnancy. Assuming 12.5% of cigarette smokers stopped smoking during pregnancy, 18.1% of all low weight births were caused by maternal smoking in 1984. The percentage for most social groups was similar. The overall attributable risk from smoking was estimated to be 12.7 low weight births per 1000 total births, with a further 12.1 per 1000 due to other factors acting in a socioeconomic gradient. We estimate that the minimum attainable low birthweight incidence in 1984 was 45.4 per 1000 total births, based on the lowest observed incidence, corrected for smoking prevalence, which was in social group II. We recommend the addition of maternal smoking information to the Korner maternity clinical options data set, to enable an accurate assessment of the risks and to provide local monitoring of initiatives to reduce smoking prevalence during pregnancy.