Research
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OBSTETRICS
The association between obstetrical interventions and late preterm birth Kate L. Bassil, PhD; Abdool S. Yasseen III, MSc; Mark Walker, MD; Michael D. Sgro, MD; Prakesh S. Shah, MD; Graeme N. Smith, MD, PhD; Douglas M. Campbell, MD; Muhammad Mamdani, PharmD; Ann E. Sprague, PhD; Shoo K. Lee, MD; Jonathon L. Maguire, MD OBJECTIVE: There is concern that obstetric interventions (prelabor cesarean section and induced delivery) are drivers of late preterm (LP) birth. Our objective was to evaluate the independent association between obstetric interventions and LP birth and explore associated independent maternal and fetal risk factors for LP birth. STUDY DESIGN: In this population-based cross-sectional study, the
BORN Information System was used to identify all infants born between 34 and 40 completed weeks of gestation between 2005 and 2012 in Ontario, Canada. The association between obstetric interventions (preterm cesarean section and induced delivery) and LP birth (34 to 36 completed weeks’ gestation vs 37 to 40 completed weeks’ gestation) was assessed using generalized estimating equation regression. RESULTS: Of 917,013 births between 34 and 40 weeks, 49,157 were
LP (5.4%). In the adjusted analysis, “any obstetric intervention” (risk
ratio [RR], 0.65; 95% confidence interval [CI], 0.57e0.74), induction (RR, 0.71; 95% CI, 0.61e0.82) and prelabor cesarean section (RR, 0.66; 95% CI, 0.59e0.74) were all associated with a lower likelihood of LP vs term birth. Several independent potentially modifiable risk factors for LP birth were identified including previous cesarean section (RR, 1.28; 95% CI, 1.16e1.40), smoking during pregnancy (RR, 1.28; 95% CI, 1.21e1.36) and high material (RR, 1.1; 95% CI, 1.03e1.18) and social (RR, 1.09; 95% CI, 1.02e1.16) deprivation indices. CONCLUSION: After accounting for differences in maternal and fetal risk,
LP births had a 35% lower likelihood of obstetric interventions than term births. Obstetric care providers may be preferentially avoiding induction and prelabor cesarean section between 34 and 37 weeks’ gestation. Key words: cesarean delivery, late preterm, maternal health, obstetric intervention, risk factors
Cite this article as: Bassil KL, Yasseen III AS, Walker M, et al. The association between obstetric interventions and late preterm birth. Am J Obstet Gynecol 2014;210:x-ex-x-ex.
P
reterm birth is the leading cause of infant morbidity and mortality and has been described as the most important perinatal challenge facing industrialized countries.1 Among preterm infants (500 g birthweight with a gestational age between 340/7 and 406/7 weeks in Ontario, Canada, between 2005 and 2012 were eligible for inclusion in this study. Women who gave birth between 410/7 and 416/7 weeks’ gestation were excluded to avoid capturing an increased risk of obstetric interventions in the 41st week of gestation. Sources of data Data were obtained from the BORN Information System (BIS), which is a provincial, internet-based maternal newborn surveillance system managed by the Better Outcomes Registry & Network (BORN Ontario). Maternal, fetal, and obstetric data were extracted for the study time period, April 1, 2004, to March 31, 2012. In a birth number validation exercise between the CIHI Discharge Abstract Database and the BIS, the BORN system captured 82% of hospital births in the 2004-2005 fiscal year and increased yearly until 100% of hospital births from 106 sites were captured by 2010-11. The BIS includes information on maternal demographic characteristics and health behaviors, preexisting maternal health problems, obstetric complications, intrapartum interventions, and birth outcomes. Various quality assurance mechanisms were used to ensure high data quality and consistency including data entry operating
www.AJOG.org manuals, automated system checks, and training sessions for data entry staff.13 A validation study of the BORN birth record system found a high level of agreement with the original patient record for many of the variables used in this study including gestational age, induced delivery and cesarean section, which had 91%, 90%, and 99% agreement with the original patient record respectively.11 The variance for percentage agreement across all variables evaluated was 97.2% (interquartile range, 93.0e99.4%).11
Exposure variables Our primary exposure was ‘any obstetric intervention’ defined as prelabor cesarean section or induced delivery. Our secondary exposures were prelabor cesarean section and induced delivery separately. To avoid overlap between obstetric intervention categories and capture of the event that primarily influenced gestational age at birth, induced deliveries were defined as those with medical or surgical intervention to initiate uterine contractions before the onset of spontaneous labor and included those that subsequently resulted in cesarean section. Prelabor cesarean sections were defined as delivery by cesarean section without prior induction of labor or spontaneous onset of labor. Spontaneous onset of labor was defined as labor that was initiated without intervention, which may have been preceded by spontaneious rupture of membranes. We also explored maternal and obstetric factors known or suspected to be associated with preterm birth. These included maternal characteristics such as maternal age at delivery, socioeconomic status, smoking during pregnancy, parity (nulliparous, primiparous, or multiparous), multifetal pregnancy, previous cesarean section, and number of previous preterm births; maternal health problems including preexisting diabetes (insulin and noninsulin dependent), gestational diabetes, chronic hypertension (hypertension that predates the pregnancy or was diagnosed before the 20th week of gestation), gestational hypertension, infection during pregnancy (composite of any periodontal, urinary tract, vaginal, or cervical infections), and obstetrical complications including
1.e2 American Journal of Obstetrics & Gynecology MONTH 2014
preeclampsia, eclampsia, placenta previa, uterine bleeding, placental abruption (premature separation of a normally implanted placenta after the 20th week of gestation and before the fetus is delivered), cord prolapse, chorioamnionitis, breech presentation and small for gestational age (
www.AJOG .org
OBSTETRICS
The association between obstetrical interventions and late preterm birth Kate L. Bassil, PhD; Abdool S. Yasseen III, MSc; Mark Walker, MD; Michael D. Sgro, MD; Prakesh S. Shah, MD; Graeme N. Smith, MD, PhD; Douglas M. Campbell, MD; Muhammad Mamdani, PharmD; Ann E. Sprague, PhD; Shoo K. Lee, MD; Jonathon L. Maguire, MD OBJECTIVE: There is concern that obstetric interventions (prelabor cesarean section and induced delivery) are drivers of late preterm (LP) birth. Our objective was to evaluate the independent association between obstetric interventions and LP birth and explore associated independent maternal and fetal risk factors for LP birth. STUDY DESIGN: In this population-based cross-sectional study, the
BORN Information System was used to identify all infants born between 34 and 40 completed weeks of gestation between 2005 and 2012 in Ontario, Canada. The association between obstetric interventions (preterm cesarean section and induced delivery) and LP birth (34 to 36 completed weeks’ gestation vs 37 to 40 completed weeks’ gestation) was assessed using generalized estimating equation regression. RESULTS: Of 917,013 births between 34 and 40 weeks, 49,157 were
LP (5.4%). In the adjusted analysis, “any obstetric intervention” (risk
ratio [RR], 0.65; 95% confidence interval [CI], 0.57e0.74), induction (RR, 0.71; 95% CI, 0.61e0.82) and prelabor cesarean section (RR, 0.66; 95% CI, 0.59e0.74) were all associated with a lower likelihood of LP vs term birth. Several independent potentially modifiable risk factors for LP birth were identified including previous cesarean section (RR, 1.28; 95% CI, 1.16e1.40), smoking during pregnancy (RR, 1.28; 95% CI, 1.21e1.36) and high material (RR, 1.1; 95% CI, 1.03e1.18) and social (RR, 1.09; 95% CI, 1.02e1.16) deprivation indices. CONCLUSION: After accounting for differences in maternal and fetal risk,
LP births had a 35% lower likelihood of obstetric interventions than term births. Obstetric care providers may be preferentially avoiding induction and prelabor cesarean section between 34 and 37 weeks’ gestation. Key words: cesarean delivery, late preterm, maternal health, obstetric intervention, risk factors
Cite this article as: Bassil KL, Yasseen III AS, Walker M, et al. The association between obstetric interventions and late preterm birth. Am J Obstet Gynecol 2014;210:x-ex-x-ex.
P
reterm birth is the leading cause of infant morbidity and mortality and has been described as the most important perinatal challenge facing industrialized countries.1 Among preterm infants (500 g birthweight with a gestational age between 340/7 and 406/7 weeks in Ontario, Canada, between 2005 and 2012 were eligible for inclusion in this study. Women who gave birth between 410/7 and 416/7 weeks’ gestation were excluded to avoid capturing an increased risk of obstetric interventions in the 41st week of gestation. Sources of data Data were obtained from the BORN Information System (BIS), which is a provincial, internet-based maternal newborn surveillance system managed by the Better Outcomes Registry & Network (BORN Ontario). Maternal, fetal, and obstetric data were extracted for the study time period, April 1, 2004, to March 31, 2012. In a birth number validation exercise between the CIHI Discharge Abstract Database and the BIS, the BORN system captured 82% of hospital births in the 2004-2005 fiscal year and increased yearly until 100% of hospital births from 106 sites were captured by 2010-11. The BIS includes information on maternal demographic characteristics and health behaviors, preexisting maternal health problems, obstetric complications, intrapartum interventions, and birth outcomes. Various quality assurance mechanisms were used to ensure high data quality and consistency including data entry operating
www.AJOG.org manuals, automated system checks, and training sessions for data entry staff.13 A validation study of the BORN birth record system found a high level of agreement with the original patient record for many of the variables used in this study including gestational age, induced delivery and cesarean section, which had 91%, 90%, and 99% agreement with the original patient record respectively.11 The variance for percentage agreement across all variables evaluated was 97.2% (interquartile range, 93.0e99.4%).11
Exposure variables Our primary exposure was ‘any obstetric intervention’ defined as prelabor cesarean section or induced delivery. Our secondary exposures were prelabor cesarean section and induced delivery separately. To avoid overlap between obstetric intervention categories and capture of the event that primarily influenced gestational age at birth, induced deliveries were defined as those with medical or surgical intervention to initiate uterine contractions before the onset of spontaneous labor and included those that subsequently resulted in cesarean section. Prelabor cesarean sections were defined as delivery by cesarean section without prior induction of labor or spontaneous onset of labor. Spontaneous onset of labor was defined as labor that was initiated without intervention, which may have been preceded by spontaneious rupture of membranes. We also explored maternal and obstetric factors known or suspected to be associated with preterm birth. These included maternal characteristics such as maternal age at delivery, socioeconomic status, smoking during pregnancy, parity (nulliparous, primiparous, or multiparous), multifetal pregnancy, previous cesarean section, and number of previous preterm births; maternal health problems including preexisting diabetes (insulin and noninsulin dependent), gestational diabetes, chronic hypertension (hypertension that predates the pregnancy or was diagnosed before the 20th week of gestation), gestational hypertension, infection during pregnancy (composite of any periodontal, urinary tract, vaginal, or cervical infections), and obstetrical complications including
1.e2 American Journal of Obstetrics & Gynecology MONTH 2014
preeclampsia, eclampsia, placenta previa, uterine bleeding, placental abruption (premature separation of a normally implanted placenta after the 20th week of gestation and before the fetus is delivered), cord prolapse, chorioamnionitis, breech presentation and small for gestational age (
