Whether you've had an easy and enjoyable pregnancy or a difficult time, pre-term labor can happen to anyone. There are many different factors that can increase the risk of an early birth, and unfortunately, some of them are completely out of your control. Research has shown that your height could affect your pregnancy, and raise your risk of going into labor early.
I spoke with Dr. Louis Muglia, the co-director of the Perinatal Institute at Cincinnati Children's Hospital Medical Center, who authored a study on the link between a mom's height and the length of her pregnancy. Muglia says he and his team didn't set out to look for that link, but instead were investigating possible genetic causes of early labor (before 37 weeks). "We've been interested in identifying genes that control birth timing for the last 15 or 20 years, and have been collecting samples from women and infants... to look at DNA in a very unbiased way," Mugler says. "As well as getting their DNA, we get a lot of other information about them, including their different body measurements."
He and his team looked at the stats for about 3,000 women who didn't have any other risk factors for pre-term births (which include preeclampsia, diabetes, and carrying multiples, according to the March of Dimes). A surprising observation jumped out at them. "We found that... maternal height was very significantly associated with the duration of the pregnancy, the weight of the baby at birth, and the length of the baby at birth." Muglia says that taller moms had longer pregnancies, and longer and heavier babies. He says the trend had been noticed before, but doctors hadn't figured out the true cause.
"It was thought that the height affects were largely reflecting nutrition, that moms that were shorter didn't have access to good nutrition and that compromised their pregnancy outcomes." But that conclusion didn't jive with what Muglia's team was seeing. "We were doing these studies in women of northern European descent, from very typical higher economic countries like Finland, Norway, and Denmark, and there's very little malnutrition going on there."
Muglia says it's not totally clear, then, what causes the connection between a mom's height and length of pregnancy. He speculates that it could be due to shorter mothers having smaller uteruses, or different metabolic rates than their taller counterparts. It's something he hopes to study further, but says there's an important conclusion to be drawn anyway. "The risk for pre-term birth isn't necessarily some acute event that happens during pregnancy. It's about how moms enter pregnancy." Knowing that there's a link also opens up many possible avenues of exploration. "Right now the things that are most predictive of having a pre-term birth is having a previous pre-term birth. Most of the time we don't have good markers for a woman that's never been pregnant before as to what her risk is."
Muglia hopes that doctors will be able to develop tests within the next few years that will help determine what a woman's risk for pre-term labor is, and even roll out possible treatments. That could potentially save millions of lives — the World Health Organization noted that complications due to pre-term births are one of the leading causes of death for children under the age of 5. Muglia says the mystery of unexplained pre-term births is one of the great unsolved questions in biology. But little by little, an answer may be getting closer.