Most pregnancies last around 40 weeks. Babies born between 37 and 42 completed weeks of pregnancy are called full term. Babies born before 37 completed weeks of pregnancy are called premature.
In the United States, about 12.8 percent of babies (more than half a million a year) are born prematurely. The rate of premature birth has increased by 36 percent since the early 1980s.
Premature babies are at increased risk for newborn health complications and lasting disabilities such as mental retardation, learning and behavioral problems, cerebral palsy, lung problems and vision and hearing loss. According to the March of Dimes website, two recent studies suggest that premature babies may be at an increased risk of symptoms associated with autism, social, behavioral and speech problems. Studies also suggest that babies born very prematurely may be at an increased risk of certain adult health problems, such as diabetes, high blood pressure and heart disease.
Now, an international team of researchers believes that by studying human evolution they may have discovered a gene linked to premature births.
In comparison to other primates and mammals, humans have relatively large heads and narrow birth canals. The researchers, at Vanderbilt University, Washington University and the University of Helsinki, believed there must have been an evolutionary pressure to “adapt and shift the time of birth” to produce a smaller baby.
They looked for DNA which showed evidence of “accelerated evolution” – genes which have mutated more in humans than in other primates. They identified 150 genes. The next step was to look for an association with premature births, so the researchers compared those 150 genes in 328 Finnish mothers, some of whom had premature births. A strong association to pre-term births was found in variants of the FSHR – or follicle stimulating hormone receptor – gene. Follicle stimulating hormone acts on receptors in the ovaries to encourage follicle (a sphere of cells containing an egg) development and production of the hormone oestrogen.
The hope is to predict which women are at greatest risk for having pre-term birth and will be able to prevent it. That would really have an impact on infant mortality and the long-term complications of being born prematurely.”
Professor Ronald Lamont, spokesperson for the Royal College of Obstetricians and Gynecologists, says the riks of premature birth is likely to be a mix of genetic and environmental factors but the study could help immensely: “In the future we will be able to identify a percentage of people at risk. It won’t be the be all and end all, but it will contribute to our knowledge.”