Graduation Year

2014

Document Type

Dissertation

Degree

Ph.D.

Degree Granting Department

Epidemiology and Biostatistics

Major Professor

Hamisu M. Salihu

Keywords

early term, elective delivery, epidemiology, health services research, infant mortality

Abstract

The length of human pregnancy, arguably the most natural of physiological processes, is undergoing subtle but consequential modification in order to adapt to modern societal demands. The gestational age distribution of births in the United States has been shifting to lower gestational ages over the past two decades, parallel to a concomitant rise in obstetrical intervention in pregnancy. The result has been an increase in elective deliveries at 37-38 weeks (early term).

A population-based retrospective cohort study of over 616,000 live-born full-term singleton infants was conducted to investigate the association between elective early term delivery and subsequent infant morbidity, mortality, and health care utilization in the first year of life. Data were examined from a statewide, multi-year, clinically-enhanced database created by linking birth certificate records to maternal and infant hospital discharge records, and to infant death certificates, for all infants born to Florida-resident mothers from 2005-09. All infants delivered to mothers with an established medical condition that could have justified early delivery were excluded from the study, as it would not be possible to determine if an early delivery in those cases was elective or medically-necessary. Based on the timing and reason for delivery initiation, the study population was categorized into four exposure groups: 1) early electively induced delivery at 37-38 weeks (EED-I), 2) early elective cesarean delivery at 37-38 weeks (EED-CS), 3) early spontaneous delivery at 37-38 weeks (ESD), 4) early medically-indicated delivery at 37-38 weeks (EID). The comparison group consisted of all expectantly managed infants who were full term deliveries (FTD) at ≥39 weeks. Adverse infant outcomes in the first year of life included respiratory morbidities, neonatal sepsis, feeding difficulties, admission to the neonatal intensive care unit, the frequency and duration of hospital encounters, and infant mortality. Multivariable generalized linear mixed models were used to estimate odds ratios (OR) or rate ratios (RR) and 95% confidence intervals (CI) between exposure and each outcome, adjusting for maternal, infant, and hospital characteristics and accounting for the correlation among infants born at the same facility.

Infants who were delivered by EED-I or EED-CS comprised 13% of the study population, and 40% of infants born in the early term period. Infants who were delivered by EED-I experienced the lowest likelihoods of respiratory morbidities, neonatal sepsis, and admission to the NICU when compared to FTD infants. In contrast, infants delivered by EED-CS had significantly increased risks several adverse birth outcomes, with magnitudes ranging from a 9% to 40% increase. Only 8.3% of all infants were re-admitted to the hospital after birth. Despite having the lowest likelihood of the birth morbidities studied, infants delivered by EED-I had a small 10-15% increased odds of being re-hospitalized in the first year of life, compared to FTD infants. These infants also had a slightly higher mean number of visits and combined LOS during post-birth hospitalizations, although the absolute differences from other exposure groups was small. Elective early term cesarean infants actually had a slightly lower risk of re-hospitalization, particularly re-hospitalizations that occurred between weeks 3-52 of life. Neonatal and post-neonatal deaths were rare events (0.3 and 1.3 deaths per 1,000 live births, respectively) in this comparatively low-risk study population. There were no differences in survival when comparing the EED-I and EED-CS groups to the FTD group.

The results of this study raise the concern that these public health efforts to reduce elective early term inductions have been based on biased evidence from a limited number of studies in which artificially elevated risks for early electively-induced infants were reported. In stark contrast to the current dogma, this study found that when a methodologically appropriate comparison group was used (i.e., expectant management), elective induction prior to 39 weeks was NOT associated with an increased risk of any adverse infant outcomes in early life. In contrast, our findings do support the avoidance of purely elective cesarean sections prior to 39 weeks in lieu of expectant management. The evidence presented in this large, methodologically-sound study should caution against a general avoidance of ALL elective early term deliveries, and foster support for continued research in this still relatively new arena.

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