The low birth-weight paradox is an apparently paradoxical observation relating to the birth weights and mortality rate of children born to tobacco smoking mothers. Low birth-weight children born to smoking mothers have a lower infant mortality rate than the low birth weight children of non-smokers. It is an example of Simpson's paradox.
Traditionally, babies weighing less than a certain amount (which varies between countries) have been classified as having low birth weight. In a given population, low birth weight babies have a significantly higher mortality rate than others; thus, populations with a higher rate of low birth weights typically also have higher rates of child mortality than other populations.
Based on prior research, the children of smoking mothers are more likely to be of low birth weight than children of non-smoking mothers. Thus, by extension the child mortality rate should be higher among children of smoking mothers. So it is a surprising real-world observation that low birth weight babies of smoking mothers have a lower child mortality than low birth weight babies of non-smokers.
At first sight these findings seemed to suggest that, at least for some babies, having a smoking mother might be beneficial to one's health. However the paradox can be explained statistically by uncovering a lurking variable between smoking and the two key variables: birth weight and risk of mortality. Both variables are acted on independently by smoking and other adverse conditions—birth weight is lowered and the risk of mortality increases. However, each condition does not necessarily affect both variables to the same extent.
The birth weight distribution for children of smoking mothers is shifted to lower weights by their mothers' actions. Therefore, otherwise healthy babies (who would weigh more if it were not for the fact their mother smoked) are born underweight. However, they still have a lower mortality rate than children who have other, more severe, medical reasons why they are born underweight.
In short, smoking is harmful in that it contributes to low birth weight which has higher mortality than normal birth weight, but other causes of low birth weight are generally more harmful than smoking.
If one corrects and adjusts for the confounding by smoking, via stratification or multivariable regression modelling to statistically control for smoking, one finds that the association between birth weight and mortality may be attenuated towards the null. Nevertheless, most epidemiological studies of birth weight and mortality have controlled for maternal smoking, and the adjusted results, although attenuated after adjusting for smoking, still indicated a significant association.
Additional support for the hypothesis that birth weight and mortality can be acted on independently came from the analysis of birth data from Colorado: compared with the birth weight distribution in the US as a whole, the distribution curve in Colorado is also shifted to lower weights. The overall child mortality of Colorado children is the same as that for US children however, and if one corrects for the lower weights as above, one finds that babies of a given (corrected) weight are just as likely to die, whether they are from Colorado or not. The likely explanation here is that the higher altitude of Colorado affects birth weight, but not mortality.
Epidemiology is the study and analysis of the distribution, patterns and determinants of health and disease conditions in a defined population.
Infant mortality is the death of an infant before the infant's first birthday. The occurrence of infant mortality in a population can be described by the infant mortality rate (IMR), which is the number of deaths of infants under one year of age per 1,000 live births. Similarly, the child mortality rate, also known as the under-five mortality rate, compares the death rate of children up to the age of five.
A cohort study is a particular form of longitudinal study that samples a cohort, performing a cross-section at intervals through time. It is a type of panel study where the individuals in the panel share a common characteristic.
Preterm birth, also known as premature birth, is the birth of a baby at fewer than 37 weeks gestational age, as opposed to full-term delivery at approximately 40 weeks. Extreme preterm is less than 28 weeks, very early preterm birth is between 28 and 32 weeks, early preterm birth occurs between 32 and 34 weeks, late preterm birth is between 34 and 36 weeks' gestation. These babies are also known as premature babies or colloquially preemies or premmies. Symptoms of preterm labor include uterine contractions which occur more often than every ten minutes and/or the leaking of fluid from the vagina before 37 weeks. Premature infants are at greater risk for cerebral palsy, delays in development, hearing problems and problems with their vision. The earlier a baby is born, the greater these risks will be.
Low birth weight (LBW) is defined by the World Health Organization as a birth weight of an infant of 2,499 g or less, regardless of gestational age. Infants born with LBW have added health risks which require close management, often in a neonatal intensive care unit (NICU). They are also at increased risk for long-term health conditions which require follow-up over time.
Birth weight is the body weight of a baby at their birth. The average birth weight in babies of European and African descent is 3.5 kilograms (7.7 lb), with the normative range between 2.5 and 4.0 kilograms. On average, babies of Asian descent weigh about 3.25 kilograms (7.2 lb). The prevalence of low birth weight has changed over time. Trends show a slight decrease from 7.9% (1970) to 6.8% (1980), then a slight increase to 8.3% (2006), to the current levels of 8.2% (2016). The prevalence of low birth weights has trended slightly upward from 2012 to the present.
Prenatal development includes the development of the embryo and of the fetus during a viviparous animal's gestation. Prenatal development starts with fertilization, in the germinal stage of embryonic development, and continues in fetal development until birth.
In causal inference, a confounder is a variable that influences both the dependent variable and independent variable, causing a spurious association. Confounding is a causal concept, and as such, cannot be described in terms of correlations or associations. The existence of confounders is an important quantitative explanation why correlation does not imply causation. Some notations are explicitly designed to identify the existence, possible existence, or non-existence of confounders in causal relationships between elements of a system.
The Hispanic paradox is an epidemiological finding that Hispanic Americans tend to have health outcomes that "paradoxically" are comparable to, or in some cases better than, those of their U.S. non-Hispanic White counterparts, even though Hispanics have lower average income and education, higher rates of disability, as well as a higher incidence of various cardiovascular risk factors and metabolic diseases.
Maternal health is the health of women during pregnancy, childbirth, and the postpartum period. In most cases, maternal health encompasses the health care dimensions of family planning, preconception, prenatal, and postnatal care in order to ensure a positive and fulfilling experience. In other cases, maternal health can reduce maternal morbidity and mortality. Maternal health revolves around the health and wellness of pregnant women, particularly when they are pregnant, at the time they give birth, and during child-raising. WHO has indicated that even though motherhood has been considered as a fulfilling natural experience that is emotional to the mother, a high percentage of women develop health problems and sometimes even die. Because of this, there is a need to invest in the health of women. The investment can be achieved in different ways, among the main ones being subsidizing the healthcare cost, education on maternal health, encouraging effective family planning, and ensuring progressive check up on the health of women with children. Maternal morbidity and mortality particularly affects women of color and women living in low and lower-middle income countries.
The paternal age effect is the statistical relationship between the father's age at conception and biological effects on the child. Such effects can relate to birthweight, congenital disorders, life expectancy and psychological outcomes. A 2017 review found that while severe health effects are associated with higher paternal age, the total increase in problems caused by paternal age is low. While paternal age has increased since 1960–1970, this is not seen as a major public health concern.
The obesity paradox is the finding in some studies of a lower mortality rate for overweight or obese people within certain subpopulations. The paradox has been observed in people with cardiovascular disease and cancer. Explanations for the paradox range from excess weight being protective to the statistical association being caused by methodological flaws such as confounding, detection bias, reverse causality, or selection bias.
The Mexican paradox is the observation that Mexicans exhibit a surprisingly low incidence of low birth weight, contrary to what would be expected from their socioeconomic status (SES). This appears as an outlier in graphs correlating SES with low-birth-weight rates. The medical causes of lower rates of low birth weights among birthing Mexican mothers has been called into question.
The Child Development Index (CDI) is an index combining performance measures specific to children—education, health and nutrition—to produce a score on a scale of 0 to 100. A zero score would be the best. The higher the score, the worse children are faring.
Tobacco smoking during pregnancy causes many detrimental effects on health and reproduction, in addition to the general health effects of tobacco. A number of studies have shown that tobacco use is a significant factor in miscarriages among pregnant smokers, and that it contributes to a number of other threats to the health of the foetus.
The Save the Children State of the World's Mothers report (SOWM report) is an annual report by the Save the Children USA, which compiles statistics on the health of mothers and children and uses them to produce rankings of more than 170 countries, showing where mothers fare best and where they face the greatest hardships. The rankings are presented in the Mothers’ Index, which has been produced annually since the year 2000.
Prenatal nutrition addresses nutrient recommendations before and during pregnancy. Nutrition and weight management before and during pregnancy has a profound effect on the development of infants. This is a rather critical time for healthy development since infants rely heavily on maternal stores and nutrient for optimal growth and health outcome later in life.
Prenatal care in the United States is a health care preventive care protocol recommended to women with the goal to provide regular check-ups that allow obstetricians-gynecologists, family medicine physicians, or midwives to detect, treat and prevent potential health problems throughout the course of pregnancy while promoting healthy lifestyles that benefit both mother and child. Patients are encouraged to attend monthly checkups during the first two trimesters and in the third trimester gradually increasing to weekly visits. Women who suspect they are pregnant can schedule pregnancy tests prior to 9 weeks gestation. Once pregnancy is confirmed an initial appointment is scheduled after 8 weeks gestation. Subsequent appointments consist of various tests ranging from blood pressure to glucose levels to check on the health of the mother and fetus. If not, appropriate treatment will then be provided to hinder any further complications.
Undernutrition in children, occurs when children do not consume enough calories, protein, or micronutrients to maintain good health. It is common globally and may result in both short and long term irreversible adverse health outcomes. Undernutrition is sometimes used synonymously with malnutrition, however, malnutrition could mean both undernutrition or overnutrition. The World Health Organization (WHO) estimates that malnutrition accounts for 54 percent of child mortality worldwide, which is about 1 million children. Another estimate, also by WHO, states that childhood underweight is the cause for about 35% of all deaths of children under the age of five worldwide.
The fetal origins hypothesis proposes that the period of gestation has significant impacts on the developmental health and wellbeing outcomes for an individual ranging from infancy to adulthood. The effects of fetal origin are marked by three characteristics: latency, wherein effects may not be apparent until much later in life; persistency, whereby conditions resulting from a fetal effect continue to exist for a given individual; and genetic programming, which describes the 'switching on' of a specific gene due to prenatal environment. Research in the areas of economics, epidemiology, and epigenetics offer support for the hypothesis.