Average Pregnancy Length Shorter in the US Than European Countries

A new study has found that the average pregnancy length in the United States (US) is shorter than in European countries. The research, led by Boston University School of Public Health (BUSPH) and Harvard Medical School, is published in PLOS One.

Analyzing gestational age patterns and timings of births

Hospital organizational structures and staffing differ across various regions of the world, which may impact pregnancy and birthing processes, in addition to pregnancy outcomes. A collaborative research study has analyzed gestational age patterns and timings of both home and hospital births to understand these differences in greater detail.

The researchers, including Professor Rachel Rowe from Oxford Population Health’s National Perinatal Epidemiology Unit (NPEU), focused their study on three countries: the US – where most women are cared for by obstetricians – and England and the Netherlands, where pregnancy care is primarily provided by midwives, with further support offered by obstetrics if required.

“For overall gestational age comparisons, we drew on national birth cohorts from the US (1990, 2014 and 2020), the Netherlands (2014 and 2020) and England (2020). Birth timing data was drawn from national data from the US (2014 and 2020), the Netherlands (2014) and from a large representative sample from England (2008–10). We compared timing of births by hour of the day in hospital and home births in all three countries,” the authors write. In total, data on over 3.8 million births in the US, 156,000 births in the Netherlands and over 56,000 births in England were assessed.

Shorter pregnancy length in the US

Rowe and colleagues found that, in the US, the average gestational age distribution declined by more than half a week between 1990 (39.1 weeks) and 2020 (38.5 weeks). In parallel, 76% of births in the US occurred prior to 40 weeks, compared to 60% in England and 56% in the Netherlands.

“The gestational age distribution and timing of home births was comparable in the three countries. Home births peaked in early morning between 2:00 am and 5:00 am. In England and the Netherlands, hospital spontaneous vaginal births showed a generally similar timing pattern to home births. In the US, the pattern was reversed with a prolonged peak of spontaneous vaginal hospital births between 8:00 am to 5:00 pm,” say the authors.

A lesson to be learned

The researchers state that this is the first international study to analyze large datasets in order to compare gestational age and birth timing in three high-income countries. Most previous research has focused largely on data obtained from individual hospitals or countries. “Dr. Eugene Declercq and I first noticed similarities and differences in patterns of the timing of birth in the US and in our birthplace data at a conference several years ago. It's gratifying to see these differences and others illuminated in this paper, as one possible contributing factor to the poorer birth outcomes we see in the US,” Rowe says.

Declercq, a professor in community health sciences at BUSPH and professor in obstetrics and gynecology at Boston University Chobanian and Avedisian School of Medicine, is the study’s first author. He adds, “Our multi-country analysis shows that the US is an outlier in gestational age distribution and timing of low-intervention hospital births.”

He notes that “there is a lesson to be learned” from countries that have more positive maternity outcomes than the US, suggesting that hospital staffing and operational plans “conform more closely to the natural patterns of birth timing and gestational age, rather than try to have birth timing fit organizational needs.”

This article is a rework of a press release issued by the Oxford Population Health’s National Perinatal Epidemiology Unit (NPEU). Material has been edited for length and content.

Reference: Declercq E, Wolterink A, Rowe R, et al. The natural pattern of birth timing and gestational age in the US compared to England, and the Netherlands. PLOS ONE. 2023;18(1):e0278856. doi:10.1371/journal.pone.0278856.