Fetal origins hypothesis

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Developmental origins of health and disease hypothesis

The developmental origins of health and disease hypothesis (also known as 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.

Background

The fetus was once believed to be a "perfect parasite," immune to harmful environmental toxins passed from the mother via the placenta. Stemming from this belief, pregnant women of the early to mid 20th century freely drank alcohol, ingested medications, smoked cigarettes, and were largely ignorant of any nutritional needs for a developing fetus. This easy going attitude about pregnancy was challenged, however, by findings relating substances ingested by a mother to tragic outcomes for a fetus. The birth defects crisis due to the medication thalidomide in the 1960s, where thousands of children were born with defects ranging from brain damage to truncated and missing arms and legs is an example of how a seemingly miracle medication (supposed to prevent morning sickness) instead had disastrous consequences. Similarly, in 1971, a drug known as DES, diethylstilbestrol, when taken by pregnant women, was found to be causing an incredibly rare vaginal cancer known as clear-cell aadenocarcinoma in young girls when the cancer was traditionally only found to affect those of post-menopausal age. This finding, in particular, demonstrates that events occurring during gestation are capable of impacting future health into adulthood. As perhaps the most well-known fetal risk, It wasn't until 1973 that fetal alcohol syndrome was first formally diagnosed, and not until 1989 that the United States government began requiring warning labels directed at pregnant women to be in place on all alcoholic beverages for sale. While the risks associated with certain medications have been well documented during pregnancy, the fetal origins hypothesis goes beyond medical substances to expand upon the effects of maternal stress, obesity, influenza, nutrition, and pollution on a developing fetus.

Barker's Hypothesis

The epidemiologist Dr. David Barker was the earliest proponent of the theory of fetal origins of adult disease, prompting the theory to be denoted as "Barker's hypothesis". In 1986, Dr. Barker published findings proposing a direct link between prenatal nutrition and late-onset coronary heart disease. He had noticed that the poorest areas of England were the same areas with the highest rates of heart disease, unearthing the predictive relationship between low birth weight and adult disease. His findings were met with criticism, mainly because at the time heart disease was considered to be predominantly determined by lifestyle and genetic factors. Since Barker's initial findings, the results have been replicated in diverse populations of Europe, Asia, North American, Africa, and Australia. In explanation of such findings, Barker suggests that fetuses learn to adapt to the environment they expect to enter into once outside of the womb. Essentially, all transmissions entering the placenta act as "postcards" giving the fetus clues as to the outside world, preparing its physiology appropriately.

Thrifty Phenotype

The thrifty phenotype hypothesis proposes that a low availability of nutrients during the prenatal stage followed by an improvement in nutritional availability in early childhood causes an increase risk of metabolic disorders, including Type II Diabetes, as a result of permanent changes in the metabolic processing of glucose-insulin determined in utero.. This predominantly affects poor communities, where maternal malnutrition may be rampant, in turn causing fetuses to be biologically programmed to expect sparse nutritional environments. But, once in the world, the readily accessible processed foods consumed are unable to be processed efficiently by individuals who had their metabolic systems pre-set to expect scarcity. This difference between expected nutritional deficits and actual food surplus results in obesity and eventually Type II Diabetes.

Epidemiological support

Epidemiological research, or the study of the health and disease patterns of certain populations, allow for controls not possible in other research avenues. When a significant situation, disaster, or event occurs across a given population, it can be assumed that the entire population is affected, thus generalizing findings across all demographics in a given group. Certain historical events provide epidemiological support for the developmental origins of health and disease, including the Dutch Hunger Winter, the influenza pandemic of 1918, the practice of Ramadan.

Pollution

Pollution may affect the health of the mother, or cross over the placenta and enter the developing fetus. Beate Ritz, a professor at UCLA, found significantly higher rates of heart malformations and valve defects in the children born to women living in highly polluted areas of Los Angeles.

Epigenetics support

Epigenetics refers to the study of the behavior of genes, and how gene express can be altered by the environment without changes made in DNA. This is believed to be particularly possible during prenatal development, and both stress and diet have been known to causes changes to a fetus. The pollution research findings are possibly linked to the altering of gene expression.

"The long-vaunted distinction between nature and nurture is therefore “outdated and unhelpful”, says Janet Currie of Princeton University’s Centre for Health and Child Wellbeing. Poor nurture during pregnancy can worsen the hand that nature has dealt."

Cancer, diabetes, mental illness, cognitive decline, osteoporosis, arthritis, obesity have all been linked with fetal origins.

Criticism of theory

Criticism of the developmental origins of health and disease can be aimed at the limitations of the research. Confounds abound due to the intertwined nature of environment before and after birth, as well as the correlational factors associated with poverty outcomes. Additionally, the use of historical and longitudinal data raises the question of reliability.

Some critics say that despite the compelling relationship documented between low birth weight and later disease, it is too soon to begin to mandate interventions aimed at increasing birth weight. Such interventions could instead have increased negative effects, until the specific mechanisms and processes are more deeply understood by which birth and early childhood weight determine development.

"Such pre-emptive targeting would constitute a radical departure from current policies that steer nearly all healthcare resources to the sick, i.e. the “pound of cure” approach. That said, the existing evidence is not sufficient to allow us to rank the cost-effectiveness of interventions targeted at women against more traditional interventions targeted at children, adolescents, or adults. For example, broadening the target population to women who might get pregnant would reduce the set of policies which are cost effective."

Implications for intervention

The implications of the developmental origins of health and disease hypothesis are akin to changing the focus of public health intervention from childhood to in utero. Because the demonstrated effects range from dramatic to subtle in the wide spread areas of educational achievement, emotional stability, career trajectory, life expectancy, disease prognosis, and psychological disorders, interventions addressing the gestational period could potentially have significant impact on individual and societal levels. Proposed interventions include the following:

• Address poverty and nutritional needs of pregnant women
• Pre-natal iodine supplements
• The federal food stamp program
• The Supplemental Feeding Program for Women, Infants, and Children (WIC)