Premature birth determined at conception

An accidental discovery has opened a new way of understanding the control of birth, Peter Pockley reports.

For every human in New Zealand there are 10 sheep. The islands’ lush pastures support a population of 39.5 million woolly mammals destined for the butcher shops and textile factories of the world.

Not quite all, though, as Kiwi scientists have capitalised on sheep for fundamental research that is proving of long-term value to human well-being. The size and physiology of sheep make them effective models for studying metabolism and reproduction and relating the results to humans.

The latest confirmation comes from the unexpected findings of research, initially aimed at better understanding the growth of the foetus in late gestation, which has shown that the crucial role of nutrition in the mother goes right back to the time of conception, rather than mainly in mid- to late-gestation as previously believed.

In humans there is a worrisome increase in the incidence of pre- term babies, bringing sickness or death for many. Typical of the Western world, premature births in New Zealand have risen from 4.3% in 1980 to 7% now. In the USA the rate has grown from 9.4% to 11.9% in the past two decades. About four in every 10 premature births are due to inflammatory conditions in the womb, but the cause or causes of others are unknown.

Now scientists at the Liggins Institute in the University of Auckland are being hailed for opening a “new window” on the processes that control the time of birth. The implications for the nutritional foundation of food aid in developing nations are so profound that an international meeting has been rapidly organised in London this month to plot the next phase in research.

Far from being experimental animals in a laboratory setting, 5- year-old pure-bred Romney ewes were mated with Dorset rams on a farm near Auckland. The things distinguishing them as “scientific” sheep were that they lived in pens, had their diet closely controlled and their weight and hormone levels measured regularly.

Neonatologist and lead author of a paper on the experiment in Science, Dr Frank Bloomfield, says Romneys were chosen as they produce a high proportion of single births. Multiple births would have confused the results. Sheep also bring a special advantage in studies of growth and development of the foetus as their gestation is highly predictable at 147 days (5 months) with a variation of only 1-2 days, much smaller than the range occurring in human births.

Dr Mark Oliver with offspring of the experimental sheep.

The sheep’s diet was controlled by feeding them with rations of concentrate that fulfilled their nutritional needs. One group of 10 ewes received a smaller amount for 60 days before conception and 30 days afterwards, while another group of eight formed a control. The amount of feed was adjusted so that each animal lost 15% of weight. Prof Peter Gluckman, Director of the Institute, says this weight loss is not unusual – and certainly not equivalent to starvation – as it is within common fluctuations that depend on the quality of pasture.

All of the ewes were allowed to lamb normally. None of the control group delivered early, whereas half of the under-nourished group delivered significantly early. On average, the undernourished group delivered 5 days earlier than the control group, and some up to 2 weeks early.

“The pre-term lambs did not weigh the same as the full-term lambs,” Bloomfield says, “but their weights, adjusted for gestation time, were no different from term or control lambs, suggesting that their weight gain was not altered. The pre-term lambs demonstrated signs of immaturity, as would be expected for lambs born pre-term, whereas those born at term did not.”

SERENDIPITY

The study was conducted during 1999 but it was only after Bloomfield began a close analysis of the results 2 years later while in Toronto that the startling nature of the experiment became clear.

Gluckman describes the discovery as a classic case of “serendipity”, an unexpected chance event that the trained mind of a scientist identifies as significant.

Team leader, Prof Jane Harding, says that a newly fertilised egg needs little nutrition but is sensitive to the nutritional and hormonal status of the mother. This suggests that “these signals may play a role in foetal growth, maturation and time of birth,” and the new findings “add a crucial layer of understanding about such links”.

A deeper appreciation of the processes at work in the womb has been obtained from biochemical analyses of hormones in the ewes, some performed in Australia by Dr David Phillips of Monash University. The Science paper, co-authored by Bloomfield, Phillips, Gluckman, Harding and four others, notes the crucial role of the hormone cortisol in triggering birth. In humans, sheep and all other mammals studied there is a surge in cortisol levels before birth.

Cortisol plays a critical role in enabling organs like the lungs to mature in preparation for life outside the womb. The sheep studies show that moderate undernutrition resulted in a surge of cortisol and another hormone, ACTH, in the foetus. ACTH is a “messenger” that is released by the pituitary gland in the brain and tells the adrenal gland to produce cortisol. In the ewes with limited nourishment, the adrenal gland in the foetus appears to have matured faster than in ewes of the control group.

Prof Peter Gluckman’s renown for studies with sheep led to the presentation of an iron sculpture that he keeps beside his desk.

This seems to be a crucial step as it was followed by pre-term birth. The authors write that this “may have major implications”.

Dr Frank Bloomfield researches sheep while caring for premature babies.

In a news report, Science records supportive comments from international experts. For example, Dr Jonathan Seckl, an endocrinologist at Western General Hospital in Edinburgh, said the findings have “potentially very interesting implications in human biology”.

THE HUMAN CONNECTION

While cautious in extrapolating the findings in sheep to humans, the research team concludes: “If these findings are applicable to human pregnancy, then a focus on events around the time of conception may hold the key to prevention of one of the major causes of pre-term birth”.

Gluckman warns that nutrition is not the only influence on the onset of birth. Stress and infections are also believed to be involved. But, proving their respective roles has been complicated by the incidence of several factors at once, especially in famine- ridden countries.

Epidemiologists have found that religious fasting in the Jewish and Muslim faiths is associated with increased proportions of premature births. Other apparent links between undernutrition and births have been observed among 800 rural villagers in India who, on average, delivered earlier than mothers in England, as well as following the stressful conditions of an earthquake in California in 1991. These observations support extrapolations of the sheep findings to humans, but none is conclusive.

Gluckman says it is too early to make confident recommendations about nutrition for women starting families on the basis of the sheep studies. Pressed for general advice, Gluckman agrees that a normal, well-rounded diet is best before and during pregnancy. He is especially keen that women maintain an adequate intake of folate. “We need to know much more about the influence of ‘macro-nutrition’ – that is, the intake of carbohydrates, fats and proteins – and ‘micronutrients’ like folate and the trace elements iron and zinc may also play crucial roles.”

Dr Michelle Glass, a pharmacologist in the Liggins Institute, is investigating the natural chemicals in the body that are similar to the active ingredients of cannabis (cannabinoids) and their receptors in the brain. The aim is to alter their molecular structure to produce fewer adverse effects on patients taking cannabis to relieve chronic pain.

Survival analysis of gestation length shows marked differences between the two groups of ewes.

* Ewes on a restricted diet

* Well-fed ewes

Bloomfield says that investigating these is the subject of further studies already underway that will also involve examining the pregnancies of sheep grazing on normal pastures. Molecular biology will be brought into play in the search for fundamental causes of premature birth.

At this month’s meeting in London, Gluckman will join other scientists, major aid agencies like USAID and the Gates Foundation, and research bodies including the Wellcome Trust in planning a strategy for research in the light of these results. The hope is that this could lead to a major shift towards maintaining nutrition for prospective mothers before, during and soon after conception rather than waiting until well into pregnancy, especially in countries that are vulnerable to the effects of malnutrition.

BOOST FOR GROWTH AND DEVELOPMENT RESEARCH

The research findings are the most significant to arise after the Liggins Institute recently added another win to its record in competitive grants when scoring, in collaboration with Massey and Otago universities, one of the New Zealand government’s seven new Centres of Research Excellence. Directed by Liggins chief Prof Gluckman, the new National Centre for Growth and Development is receiving operational funding of NZ$12.5 million over 3 years

The Centre is combining basic \biomedical techniques with experimental and clinical physiology to develop new preventative and therapeutic approaches to human health and improve animal productivity in agriculture. The Centre’s research focuses on the early periods of life, such as the causes and consequences of low birth weight and prematurity.

The Centre’s research falls into four main themes:

* the causes and consequences of low birth weight, including what pregnant women should eat;

* gene-environment interactions in growth and disease;

* saving the very immature brain (e.g. is it possible to protect white matter in the immature brain?); and

* treating neurological disease in adults (e.g. can we identify novel neuroprotective and anti-inflammatory molecules?).

It is also investigating:

* how genes and the environment interact to regulate growth, development and disease;

* how to prevent brain injury in newborn babies; and

* developmental biology therapies for neurological disease in adults.

Prof Christine Winterbourn of the Christchurch School of Medicine (a branch of Otago University) says her group is looking for “markers” of injury to the brain and lung. Injury to the white matter of the brain is common among premature babies and can lead to palsy, while lung disease can become chronic or fatal.

It would be a great step if markers can be found that indicate damage from oxidants and free radicals (rapidly reactive molecules with an unpaired electron). Funds for collaboration will enable them to conduct trials with the well-established animal models of the Auckland section of the new Centre.

Around 2500 babies are born in New Zealand each year with mild, moderate or severe brain injury. Gluckman said: “A 20% reduction would save emotional burdens and costs to many hundreds of new families each year and more than NZ$500 million in added lifetime cost to health, educational and support services. The biology of growth and development is also the basis of New Zealand’s pastoral agriculture.”

Copyright Control Publications Pty Ltd Jul 2003