The influence of interpregnancy interval on infant mortality

doi:10.1016/j.ajog.2016.12.018

American Journal of Obstetrics and Gynecology

Volume 216, Issue 3, March 2017, Pages 316.e1-316.e9

Presented as a poster at the annual meeting of the Central Association of Obstetricians and Gynecologists, Las Vegas, NV, Oct. 26-29, 2016.

https://doi.org/10.1016/j.ajog.2016.12.018 Get rights and content

Background

In Ohio, the infant mortality rate is above the national average and the black infant mortality rate is more than twice the white infant mortality rate. Having a short interpregnancy interval has been shown to correlate with preterm birth and low birthweight, but the effect of short interpregnancy interval on infant mortality is less well established.

Objective

We sought to quantify the population impact of interpregnancy interval on the risk of infant mortality.

Study Design

This was a statewide population-based retrospective cohort study of all births (n = 1,131,070) and infant mortalities (n = 8152) using linked Ohio birth and infant death records from January 2007 through September 2014. For this study we analyzed 5 interpregnancy interval categories: 0-<6, 6-<12, 12-<24, 24-<60, and ≥60 months. The primary outcome for this study was infant mortality. During the study period, 3701 infant mortalities were linked to a live birth certificate with an interpregnancy interval available. We calculated the frequency and relative risk of infant mortality for each interval compared to a referent interval of 12-<24 months. Stratified analyses by maternal race were also performed. Adjusted risks were estimated after accounting for statistically significant and biologically plausible confounding variables. Adjusted relative risk was utilized to calculate the attributable risk percent of short interpregnancy intervals on infant mortality.

Results

Short interpregnancy intervals were common in Ohio during the study period. Of all multiparous births, 20.5% followed an interval of <12 months. The overall infant mortality rate during this time was 7.2 per 1000 live births (6.0 for white mothers and 13.1 for black mothers). Infant mortalities occurred more frequently for births following short intervals of 0-<6 months (9.2 per 1000) and 6-<12 months (7.1 per 1000) compared to 12-<24 months (5.6 per 1000) (P < .001 and <.001). The highest risk for infant mortality followed interpregnancy intervals of 0-<6 months (adjusted relative risk, 1.32; 95% confidence interval, 1.17–1.49) followed by interpregnancy intervals of 6-<12 months (adjusted relative risk, 1.16; 95% confidence interval, 1.04–1.30). Analysis stratified by maternal race revealed similar findings. Attributable risk calculation showed that 24.2% of infant mortalities following intervals of 0-<6 months and 14.1% with intervals of 6-<12 months are attributable to the short interpregnancy interval. By avoiding short interpregnancy intervals of ≤12 months we estimate that in the state of Ohio 31 infant mortalities (20 white and 8 black) per year could have been prevented and the infant mortality rate could have been reduced from 7.2-7.0 during this time frame.

Conclusion

An interpregnancy interval of 12-60 months (1-5 years) between birth and conception of next pregnancy is associated with lowest risk of infant mortality. Public health initiatives and provider counseling to optimize birth spacing has the potential to significantly reduce infant mortality for both white and black mothers.

Introduction

Infant mortality is defined as a death of a baby in the first year of life and the infant mortality rate (IMR) is the number of infant deaths for every 1000 live births.1, 2 Infant mortality is often used as an indicator of the overall health of a community or population because it is a reflection of a combination factors including maternal health, quality and access to medical care, and socioeconomic status.³ The US IMR has improved in recent years but remains one of the highest among developed countries.³ Unfortunately in Ohio the IMR is higher than the national average. In 2014 there were 955 infant deaths with an IMR of 6.8, which is 13% higher than the national average of 6.0.⁴ In the same year in Cincinnati the IMR was even higher at 8.8 with a 10-year average IMR of 10.3 (Ohio Department of Health, 2014).⁴ Even more striking is the disparity in the IMR by race with the black IMR more than twice the white IMR (14.3 vs 5.3 in 2014).⁴

The leading causes of infant mortality are well documented and have been shown to be related to preterm birth, small-for-gestational-age (SGA) births, sleep-related deaths, and birth defects.⁵ There are a multitude of risk factors that contribute to these leading causes of infant mortality; some, such as smoking, may contribute to >1 of the leading causes. Smoking throughout pregnancy results in an increased risk of preterm birth⁶ and fetal growth restriction.⁷ Additionally, Dietz et al⁸ estimate that 5.3-7.7% of preterm deliveries, 23.2-33.6% of sudden infant death syndrome, and 5.0-7.3% of preterm-related deaths are directly attributable to prenatal smoking.⁸ Other major risk factors that contribute to infant mortality include maternal health status and social determinants of health including racism, poverty, poor nutrition, and poor education.⁵ An additional risk factor that has consistently been correlated with many of the adverse perinatal outcomes associated with infant mortality is having a short interpregnancy interval (IPI).⁹ Specifically, a short IPI carries an increased risk of preterm birth, SGA births, and birth defects.10, 11, 12, 13, 14 Similarly to smoking, having a short IPI likely has a complex multifactorial effect on infant mortality.

The exact mechanism by which having a short IPI leads to adverse perinatal outcomes is not entirely understood, but it has been shown that short IPI increases the risk of uterine rupture in women attempting vaginal birth after cesarean, premature rupture of membranes, endometritis, third-trimester bleeding, placenta previa, placental abruption, maternal death, and anemia.15, 16 One popular explanation in the literature that may lead to these adverse outcomes is the possibility of maternal nutritional depletion syndrome.¹⁷ This hypothesis proposes that closely spaced pregnancies worsen the maternal nutritional status because of the limited recovery time after the stress of the first pregnancy and subsequent postpartum breast-feeding. This impaired maternal nutritional status then increases the risk of adverse perinatal outcomes.¹⁸

A short IPI may subsequently lead to an increased risk of infant mortality via the adverse outcomes that place infants at an increased risk of death or via another unidentified mechanism. Regardless, reduction and prevention of short IPIs is a potentially achievable intervention to reduce the IMR especially in high-risk groups. Many of the studies that looked at the effect of IPI on infant mortality thus far looked at different IPIs, failed to control for appropriate confounding variables, had small sample sizes, are now out of date, or were either done outside of the United States or in United States with a notably different patient population from that seen in the Midwest.10, 19 This study examines the effects of IPI on infant mortality using linked recent Ohio Birth and Infant Death Certificate records.

Section snippets

Materials and Methods

We performed a statewide population-based retrospective cohort study of all births (n = 1,131,070) and infant deaths (n = 8152) using linked Ohio birth and infant death records from January 2007 through September 2014. The protocol for this study was approved by the human subjects institutional review board of the Ohio Department of Health and a deidentified data set extracted from both live birth and infant death certificates was provided for this analysis. This study was exempt from review by

Results

Short IPIs were common in Ohio during the study period with 20.5% of all multiparous births, 20.0% of births to multiparous white mothers, and 23.6% of births to multiparous black mothers following an IPI of <12 months (Figure 2). Although the percentage of births with a short IPI was high in our study, the percentage of births with a short IPI among those that resulted in an infant death was even higher at 34.3%.

When comparing the sociodemographic characteristics of the women with very short

Comment

In this population-based study spanning 7 years and 9 months of births in the state of Ohio, we found that a short IPI of <12 months is associated with significantly increased risk of infant mortality even after adjustment for confounding socioeconomic and maternal characteristics. This is especially true for very short IPIs of <6 months. Using attributable risk calculations we estimate that 240 infant deaths could have been prevented by eliminating short IPIs. This is an important finding that

References (28)

E. Moore et al.
Relationship of trimester-specific smoking patterns and risk of preterm birth
Am J Obstet Gynecol
(2016)
P.M. Dietz et al.
Infant morbidity and mortality attributable to prenatal smoking in the US
Am J Prev Med
(2010)
I. Chen et al.
Relationship between interpregnancy interval and congenital anomalies
Am J Obstet Gynecol
(2014)
A. Conde-Agudelo et al.
Effects of birth spacing on maternal health: a systematic review
Am J Obstet Gynecol
(2007)
E.A. DeFranco et al.
Influence of interpregnancy interval on neonatal morbidity
Am J Obstet Gynecol
(2015)
N.E. Reichman et al.
Validation of birth certificate data. A study of women in New Jersey's HealthStart program
Ann Epidemiol
(2001)
P.M. Dietz et al.
Validation of obstetric estimate of gestational age on US birth certificates
Am J Obstet Gynecol
(2014)
Eunice Kennedy Shriver National Institute of Child Health and Human Development. Infant mortality: topic information....
Centers for Disease Control and Prevention. Infant mortality. Available from:...
M.F. MacDorman et al.
International comparisons of infant mortality and related factors: United States and Europe, 2010
Natl Vital Stat Rep
(2014)

Ohio Department of Health. Ohio infant mortality data: general findings. Available from:...

Ohio Collaborative to Prevent Infant Mortality. Ohio infant mortality reduction plan 2015-2020. Available from:...

K. Blatt et al.

Association of reported trimester-specific smoking cessation with fetal growth restriction

Obstet Gynecol

(2016)

World Health Organization; Department of Reproductive Health and Research. Report of a WHO technical consultation on...

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Earlier studies have proposed a link between the Interpregnancy Interval (IPI) and unfavorable birth outcomes. However, it remains unclear if the outcomes of previous births could affect this relationship. We aimed to investigate whether the occurrence of adverse outcomes–small for gestational age (SGA), preterm birth (PTB), and low birth weight (LBW)–at the immediately preceding pregnancy could alter the association between IPI and the same outcomes at the subsequent pregnancy.
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Among 4,788,279 births from 3,804,152 mothers, absolute risks for subsequent SGA, PTB, and LBW were higher for women with more adverse outcomes in the preceding delivery. The RR of SGA and LBW for IPIs <6 months were greater for women without previous adverse outcomes (SGA: 1.44 [95% Confidence Interval (CI): 1.41–1.46]; LBW: 1.49 [1.45–1.52]) compared to those with three previous adverse outcomes (SGA: 1.20 [1.10–1.29]; LBW: 1.24 [1.15–1.33]). IPIs ≥120 months were associated with greater increases in risk for LBW and PTB among women without previous birth outcomes (LBW: 1.59; [1.53–1.65]; PTB: 2.45 [2.39–2.52]) compared to women with three adverse outcomes at the index birth (LBW: 0.92 [0.78–1.06]; PTB: 1.66 [1.44–1.88]).
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Short interpregnancy interval has been shown to be a key contributor to infant mortality. Black pregnant people have a higher incidence of short interpregnancy interval than people of other races and ethnicities, as well as higher rates of infant mortality. Understanding the factors related to racial disparities in short interpregnancy interval and infant mortality are a public health priority.
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: Supported by the Perinatal Institute, Cincinnati Children’s Hospital Medical Center, and March of Dimes Prematurity Research Center Ohio Collaborative, Grant 22-FY14-470.

: The authors report no conflict of interest. This study includes data provided by the Ohio Department of Health, which should not be considered an endorsement of this study or its conclusions.

: Cite this article as: McKinney D, House M, Chen A, et al. The influence of interpregnancy interval on infant mortality. Am J Obstet Gynecol 2017;216:316.e1-9.

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Meeting PapersCAOG PapersThe influence of interpregnancy interval on infant mortality

Background

Objective

Study Design

Results

Conclusion

Introduction

Section snippets

Materials and Methods

Results

Comment

Am J Obstet Gynecol

Am J Prev Med

Am J Obstet Gynecol

Am J Obstet Gynecol

Am J Obstet Gynecol

Ann Epidemiol

Am J Obstet Gynecol

International comparisons of infant mortality and related factors: United States and Europe, 2010

Natl Vital Stat Rep

Association of reported trimester-specific smoking cessation with fetal growth restriction

Obstet Gynecol

Meeting Papers
CAOG Papers
The influence of interpregnancy interval on infant mortality