“There is a lot of public concern about the increasing rates of preterm birth, however, when you consider that newborn deaths are decreasing, the overall increase in preterm birth may not necessarily be a bad thing,” explains Sara Simonsen, PhD, who recently published a study in BJOG: An International Journal of Obstetrics and Gynaecology. She looked at patterns and risk factors for preterm births among mothers who have had a minimum of three children.
She points out that the mortality for preterm babies has decreased over the last decade; this is particularly true among women receiving medical interventions to deliver babies prematurely in situations where health care providers believe their babies will be better off outside of the womb. She points out that this type of intervention through C-sections or inductions (inducing labor) is one reason there has been a rise in preterm births. “If you look at the deaths in newborn babies, they have gone down even though early births have gone up,” says Simonsen.
While traditionally preterm births have been lumped into one category, in her research, Simonsen teased out specific risk factors influencing different subtypes of preterm birth. Did a doctor initiate labor in a woman? Did her water break early on its own or did she have preterm labor? “The big picture is that preterm birth isn’t just one condition. You really need to divide up preterm birth in order to fully understand what is happening,” explains Simonsen.
Some of the risk factors Simonsen found were different depending on what type of preterm births the mother had in the past. For example, low weight during pregnancy was a factor if the mother went into labor on her own but not a factor leading to medical intervention. Another notable risk factor that was found for all preterm birth subtypes was how long mothers waited between pregnancies. Those who got pregnant before a two to three-year gap were at greater risk of having a recurrent preterm birth if they already had a history of preterm birth. This is important because women at risk for recurrent preterm birth can be guided to space their pregnancies in order to reduce their risk for recurrence.
The Utah Population Database, a resource unique to Utah, allowed Simonsen to analyze this information from maternally-linked Utah birth certificates for over 70,000 women. The Utah Population Database uses a variety of public records to identify births occurring in the same woman over time. This information is hard to come by in other areas of the country because maternally-linked birth records are not generally available.
“Understanding patterns of pre-term births in different woman allows us to predict the probability of recurrent preterm birth happening in other women with a similar history,” says Simonsen, who was born prematurely herself, weighing just under 4 lbs. Her earlier work as a labor and delivery nurse spurred on her interest in reproductive health and birth outcomes; now, as a Visiting Instructor in the Division of Public Health at the University of Utah, it is the public health perspective that interests her.
In short, Simonsen says, “Different pathways can lead to recurrent preterm birth, and there are some different risk factors associated with these pathways.”
Read Simonsen's published study.