Stillbirths Up, Infant Deaths Down, in Years After 39-Week Rule

Troy Brown, RN

October 29, 2019

Following widespread implementation of the rule that reduced elective deliveries prior to 39 weeks' gestation — adopted in 2010 — stillbirths increased but infant mortality decreased, a new study has found. The researchers say the results should be interpreted carefully, however.

"Although the outcomes of interest were rare in both cohorts examined, the risk of stillbirth appears to be offset by a reduction in infant death at term.

These findings should be interpreted with caution and we acknowledge the concern raised by any gains in infant death reductions being balanced by increased stillbirths," explain the investigators, led by Rachel A. Pilliod, MD.

Pilliod, of the Department of Obstetrics and Gynecology at Oregon Health & Science University in Portland, and colleagues published their findings yesterday in JAMA Pediatrics.

Although most research has found no increase in stillbirth rates after the adoption of the 39-week rule, two prior studies suggested stillbirth rates may have increased, the researchers write.

No Difference in Overall Mortality

Given the inconsistent previous findings, coupled with the policy goal of reducing adverse perinatal outcomes, Pilliod and colleagues used birth and infant death certificate period-linked files from the National Center for Health Statistics to compare stillbirth and infant death rates in the years before and after the 2010 adoption of the 39-week rule, to determine the association with overall mortality.

The distribution of deliveries at 37 through 40 weeks changed significantly during the preadoption period (births between 2008 and 2009) and those in the postadoption period (between 2011 and 2012).

Deliveries at 37 and 38 weeks fell 0.06% and 2.5%, respectively, and deliveries at 39 and 40 weeks rose 6.8% and 0.2%, respectively, during the postadoption period compared with the preadoption period (P < .001).

There were 6848 (0.09%) stillbirths in the preadoption cohort and 7088 (0.10%) in the postadoption cohort (P < .001) (difference in incidence, 0.81 additional stillbirths per 10,000 pregnancies).

Infant deaths fell over time; there were 15,686 deaths (0.21%) during the preadoption period and 13,981 deaths (0.20%) during the postadoption period (P < .001) (difference in incidence, 1.37 fewer deaths per 10,000 pregnancies).

"This finding is consistent with previous reports of infant death declining nationally during the course of our study period," the authors write.

Overall mortality — infant deaths and stillbirths combined — fell from 0.31% (22,534 infant deaths/stillbirths) during the preadoption period to 0.30% (21,069 infant deaths/stillbirths) during the postadoption period (P = .06), a difference that was not statistically significant.

The researchers calculated the overall mortality difference as 0.56 fewer deaths per 10,000 deliveries during the postadoption period.

"When considering overall mortality, we did not find a statistically significant difference between the preadoption and postadoption periods," they stress.

Strengths and Limitations

Study strengths include its "large, diverse patient population" and the fact that it compares overall perinatal mortality up until 365 days after delivery, and not only stillbirth, the researchers say.

"These findings are in agreement with other studies examining policies aimed at reducing unindicated deliveries before 39 weeks, but this is the first study, to our knowledge, to examine the outcomes of a nationwide quality measure," they explain.

Two temporal changes may have biased the findings in opposite directions, and the researchers say their counterfactual model minimized the outcome of these changes; still, they estimate that up to 34.2% of the mortality reduction over time could be associated with widespread adoption of the 39-week rule.

They also acknowledge that by only examining mortality and not morbidity, they have taken a "narrow view of the outcome to patients and health care systems from morbidity in the early-term period."

"Despite these limitations, this work adds to the discussion of early-term deliveries by examining the outcome of a widely adopted policy shift that put into practice expectant management before 39 weeks if delivery was not indicated for maternal or fetal factors," they conclude.

No funding source for the study was listed with the article. The authors have disclosed no relevant financial relationships.

JAMA Pediatr.  Published online October 28, 2019. Full text

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