Short women’s shorter pregnancies big worry

When Louis Muglia and a group of fellow researchers studied nearly 3,500 mothers and their babies in Finland, Denmark and Norway, they noticed a curious pattern: The data suggested that shorter mothers had shorter pregnancies, smaller babies and a higher risk for preterm births.

“The relatively shorter you were, the relatively shorter your pregnancy was,” said Muglia, director of the Center for Prevention of Preterm Birth at Cincinnati Children’s Hospital. “This was manifested in each of the three populations.”

The differences were small — each increase of 1 centimeter in height translated to about 0.4 gestational days — but statistically significant. Muglia said the findings, published Tuesday in the journal PLOS Medicine, might eventually offer one clue in helping to combat a problem that affects millions of babies around the world each year.

The United States has one of the highest rates of preterm births of any resource-rich country. Preterm birth affects nearly a half-million U.S. babies each year, and related complications account for roughly a third of all infant deaths, according to the Centers for Disease Control and Prevention. Premature births also result in a range of serious health problems, from vision loss to neurological disabilities.

Of course, a large body of research has shown that many elements can contribute to preterm births and affect the size and health of an infant. They include medical factors such as a mother’s weight and disease history, behavioral factors such as stress levels and tobacco or alcohol use, and environmental factors such as a lack of prenatal care and exposure to polluted air or drinking water.

But Tuesday’s study suggests that genetic factors related to a mother’s height also shape the fetal environment and influence the length of a pregnancy.

“Our study suggests it is the mom’s height itself that is helping to determine the length of gestation,” Muglia said. “It’s part of the equation.”

The explanation for why height helps determine how long a pregnancy lasts remains unclear, he said. Some experts believe height influences uterine and pelvic size, meaning babies inside of smaller mothers have less room to grow and develop. Another theory is that smaller women have a lower “basal metabolic rate” — the amount of energy needed to support the body’s basic functions while at rest — that limits the amount of nutrition they can provide to a developing fetus.