Caroline Helwick

February 05, 2016

ATLANTA — Implementation of "the 39-week rule" — which mandates that the elective delivery of babies not occur before a gestational age of 39 weeks without appropriate indication — could be increasing the number of term stillbirths, new research shows.

Investigators found that the proportion of term stillbirths rose from 1.103 per 1000 deliveries before the rule was adopted to 1.177 per 1000 after.

"This study raises the possibility that the 39-week rule may be causing serious unintended harm," said James Nicholson, MD, from the Department of Family and Community Medicine at the Penn State Milton S. Hershey Medical Center in Pennsylvania.

"Term stillbirth is clearly one of worst obstetrical outcomes, and it occurs with relatively high frequency — in one per 1000 deliveries that reach 37 weeks," he explained. "We should place a high priority on determining the causes, developing preventive interventions, and studying factors suspected of producing this truly horrible outcome."

"Unless or until high-quality research is published that proves that the 39-week rule does not increase term stillbirth rates, the forced imposition of the 39-week rule should be immediately reconsidered," he said here at the Society for Maternal-Fetal Medicine 2016 Pregnancy Meeting.

The 39-week rule may be causing serious unintended harm.

The 39-week rule was adopted after several studies suggested that the induction of labor and early-term delivery are harmful. However, "these studies contained clearly identifiable flaws," Dr Nicholson pointed out. They were retrospective cohort studies, suffered from confounding by indication, and used incorrect modeling.

In addition, the studies "failed to consider ecological fallacy, which is that we should not determine the treatment of an individual patient based on studies that examine population-based data," he said. "Ecological cohort studies should rarely be used to generate policy, yet that's what I think we did."

"Even at the rule's inception, there were concerns — largely based on the known association between increasing gestational age and the increased risk of term stillbirth, which was shown in a number of studies," he reported.

Although anecdotal reports of increased rates of term stillbirth and concerns from patient advocacy groups boosted apprehension about the rule, other studies failed to find an association between gestational age and stillbirth, he acknowledged.

Dr Nicholson and his colleagues asked state health departments to provide data on term births and term stillbirths by week of gestational age for the 3 years before and the 3 years after the 2010 adoption of the rule (2007 to 2013).

They obtained approximately 86% of the data they were looking for; they got complete data from 34 states, partial data from 12, and no usable data from five.

The investigators evaluated changes in the timing of term births and changes in the patterns and rates of term stillbirths for the 6-year study period.

More Stillbirths

"Our analysis clearly showed a reduction in the proportion of births occurring at 38 weeks and increasing in the thirty-ninth week," said Dr Nicholson. "The greatest increases in term stillbirth occurred at 37, 38, and 39 weeks of gestation," he noted, which is "right where the 39-week rule is working."

"An increasing number of women had the timing of their delivery delayed until the full-term period," he reported.

There was a significant increase in the proportion of term stillbirths after adoption of the rule; from 2007 to 2009, the proportion was 1.103 per 1000 deliveries, whereas from 2011 to 2013, it was 1.177 per 1000 (relative risk [RR], 1.07; 95% confidence interval, 1.038 - 1.096).

"Granted, the relative risk of 1.07 is low, but the confidence interval comes nowhere near to crossing 1," Dr Nicholson pointed out.

Changes were more common in the larger states. In Ohio, for example, a "significant and clinically important increase" was observed, from 1.04 per 1000 deliveries before the rule was adopted to 1.26 per 1000 deliveries after (RR, 1.21), he said.

Continuous distribution is seen across time, with a regression line that has a P value of .034. The slope of the change is an increase of 0.0186 per 1000 deliveries per year.

"Given an increase of 0.0186 per 1000 per year, given six yearly intervals from 2007 to 2013, and assuming 3.4 million term births per year in the United States, there could be 335 more term stillbirths in 2013 than in 2007," Dr Nicholson estimated.

"These are not just statistics," he explained, "they are real situations."

Dr Nicholson acknowledged that this retrospective ecological cohort study had confounding factors, and that the investigators "can only identify associations, not causation." However, "a causal connection is plausible," he maintained, "and, I think, probable."

"There is cause for concern," he concluded.

Hotly Debated

After the presentation, some members of the audience suggested that the benefits of the 39-week rule undoubtedly outweigh any risks. According to one physician, "We have achieved a lot by implementing the 39-week rule, and I caution against the suggestion that we need to go back to where we were before."

"Our belief that the rule improves outcomes is based on ecological cohort studies but is not proven in clinical practice," Dr Nicholson countered. In fact, a literature search for articles proving clinical benefit turned up nothing, he reported.

One study showed, for example, that admissions to neonatal intensive care units actually increased over time (JAMA Pediatr. 2015;169:855-862).

Readiness for delivery is a nuanced, multifactorial judgment call by the clinician, and not all providers take the time to consider all the variables, said Laxmi Baxi, MD, from the New York University Langone Medical Center in New York City.

"A number of factors may coexist," Dr Baxi told Medscape Medical News. "For example, the patient may have a little diabetes that is supposedly controlled, but how well is it controlled? Do you know? Such things besides gestational age have to be taken into consideration," she explained. "Interpretation of these factors is extremely important."

She also emphasized the need to understand more about the pathophysiology of the stillbirths. "Unless we know the cause, we can't say it's related to the 39-week rule," Dr Baxi pointed out. "Over time, we have fewer 'unrecognized causes,' but there still are some."

"I agree that the incorporation of the 39-week rule took out the thought process, at times, and clinical decision-making for providers," said session moderator Cynthia Gyamfi-Bannerman, MD, from the perinatal clinic at the Columbia University Medical Center in New York City.

"I'm not sure it needs to be dropped, but I do think some portions of the rule need to be revisited," she said.

Dr Nicholson, Dr Baxi, and Dr Gyamfi-Bannerman have disclosed no relevant financial relationships.

Society for Maternal-Fetal Medicine (SMFM) 2016 Pregnancy Meeting: Abstract 22. Presented February 4, 2016.


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