The 39-week rule is now a strict clinical guideline that is enforced by
professional organizations, governmental agencies and the medical insurance
industry in US.
In November 2013, ACOG
and Society for Maternal and Fetal medicine(SMFM) made a recommendation of replacing the use of “ term” pregnancy which accommodated gestations
between 37 wks to 42 wks with the following designations:
• Early term: 37 weeks through 38 weeks and 6 days• Full term: 39 weeks through 40 weeks and 6 days
• Late term: 41 weeks through 41 weeks and 6 days
• Postterm: 42 weeks and beyond
These changes were made by growing research evidence, a part
of which has been led by Eunice Kennedy Shriver National Institute of Child Health and Human Development, indicating that key developmental process for
the fetus continue well beyond 37 wks till 39 wks. They also advocated that “Babies
born at or after 39 weeks have the best chance at healthy outcomes compared to
those born before 39 weeks.”
It was seen that the percentage of infants born preterm declined for the seventh straight year in 2013. The NIH also published a report that shows a decline in induction of labor for singleton birth in year 2011 (23.7%) and 2012 (23.3%),after
20 years of consecutive increases. There was also a decline in Early Elective Deliveries across the United States, from 17%
of babies in the United
States were delivered before 39 weeks in
2010 to a sharp decline to 4.6% in 2013.
But, two recent studies, one by Dr. Nicholson presented at Society
for Maternal-Fetal Medicine (SMFM) 2016 Pregnancy Meeting and the other by Dr Jason
Salemi, assistant professor of family and community medicine at Baylor and lead
author of the study advise caution against the universal application of the
rule.
According to Dr Nicholson "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.
He advocated an urgent need of high quality research in this area, and until we get the evidence the forced imposition of the 39-week rule should be looked into. The 39 weeks rule was put into action after results of many studies, but he said that all those studies were flawed; they suffered from incorrect modeling, were retrospective cohort studies and the confounders were not corrected for.
He further went to add that "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."
Dr. Nicholson and his colleagues requested the state health department to provide them with data on term still births and term births segregated according to the weeks of gestation for 3 years before and 3 years after the rule was in enforced. The data clearly showed an increase in deliveries at 39 weeks. He said that "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."
The team observed a clear increase in number of stillbirths when the rule was implemented, 1.103 per 1000 deliveries in 2007-2009 to 1.177 per 1000 in 2011-2013. He further estimated that it accounts for additional 335 more term stillbirths in 2013 than in 2007. He acknowledged some shortcoming of his retrospective cohort study, saying it only identifies association, not causation.
A study published in JAMA paediatric, documented that during this period admission to NICU increased sharply.
The paper was a topic of hot debate and some physicians suggest that benefit of the rule outweigh the risk.
Dr. Baxi from New York University Langone Medical Center in New York City Opined that timing of delivery is refined decision depending on many variable and it should be individualized according to the circumstances and not governed by a rule .
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.
Dr Jason also saw limitations in many studies used to justify the 39-week rule. They conducted a retrospective cohort study, used state health data on 675,000 infants and found equivocal results in elective cesarean sections at 37-38 weeks and those delivered after 39 weeks.
“Each pregnancy is unique,” He said. “I cannot overstate the importance of open and ongoing communication between pregnant women and their healthcare providers so that the potential risks and benefits of any pregnancy-related decision are understood fully.”
Many other studies also have challenged the “39 weeks rule”. A study by Hart et al published in ACOG challenged the application of rule in Women who had prior C-sections. They conclude that their findings suggest the optimal time for scheduled delivery of women with 2 previous cesarean section deliveries is between 38 wks 0 and 38wk 6 days and between 37 wks 0 and 37 wks 6 days for women with ≥ 3 previous cesarean section deliveries
Some physicians said that they do not think that the rule should be dropped entirely but needs to be revisited.
References:
Hart L, Refuerzo J, Sibai B, Blackwell S. Abstract 40:
Should the “39 week rule” apply to women with multiple prior cesarean
deliveries? American Journal of
Obstetrics & Gynecology 2014; 210(1 Supplement): S27, January 2014
