Editing Infant mortality (section)

==== Premature birth ====
{{Main|Preterm birth}}
Premature, or [[preterm birth]] (PTB), is defined as birth before a [[gestational age]] of 37 weeks, as opposed to full term birth at 40 weeks. This can be further sub-divided in various ways, one being: "mild preterm (32–36 weeks), very preterm (28–31 weeks) and extremely preterm (<28 weeks)".<ref name="Moutquin-2003">{{Cite journal |vauthors=Moutquin JM |date=April 2003 |title=Classification and heterogeneity of preterm birth |journal=BJOG |volume=110 |issue=Suppl 20 |pages=30–3 |doi=10.1046/j.1471-0528.2003.00021.x |pmid=12763108 |s2cid=33268768 |doi-access=free}}</ref>  A lower gestational age increases the risk of infant mortality.<ref name="harrison-2016">{{Cite journal |vauthors=Harrison MS, Goldenberg RL |date=April 2016 |title=Global burden of prematurity |journal=Seminars in Fetal & Neonatal Medicine |volume=21 |issue=2 |pages=74–9 |doi=10.1016/j.siny.2015.12.007 |pmid=26740166}}</ref>

Between 1990 and 2010 prematurity was the second leading cause of worldwide mortality for neonates and children under the age of five.<ref name="Blencowe" /> The overall PTB mortality rate in 2010 was 11.1% (15 million deaths) worldwide and was highest in low to middle-income countries in sub-Saharan Africa and south Asia (60% of all PTBs), compared with high-income countries in Europe or the United States.<ref name="Blencowe">{{Cite journal |display-authors=6 |vauthors=Blencowe H, Cousens S, Oestergaard MZ, Chou D, Moller AB, Narwal R, Adler A, Vera Garcia C, Rohde S, Say L, Lawn JE |date=June 2012 |title=National, regional, and worldwide estimates of preterm birth rates in the year 2010 with time trends since 1990 for selected countries: a systematic analysis and implications |url=https://researchonline.lshtm.ac.uk/id/eprint/40396/1/1-s2.0-S0140673612608204-main.pdf__tid%3D6e9a5226-c455-11e5-8722-00000aacb362%26acdnat%3D1453830871_1bfa5cad3ce2895d33a963f1f360c67a |journal=Lancet |volume=379 |issue=9832 |pages=2162–72 |doi=10.1016/s0140-6736(12)60820-4 |pmid=22682464 |s2cid=253520}}</ref>{{Failed verification|date=July 2023}} Low-income countries also have limited resources to care for the needs of preterm infants, which increases the risk of infant mortality. The survival rate in these countries for infants born before 28 weeks of gestation is 10%, compared with a 90% survival rate in high-income countries.<ref>{{Cite book |last=March of Dimes Birth Defects Foundation. |title=Born too soon : the global action report on preterm birth |publisher=World Health Organization |year=2012 |isbn=978-92-4-150343-3 |oclc=1027675119}}</ref> In the United States, the period from 1980 to 2000 saw a decrease in the total number of infant mortality cases, despite a significant increase in premature births.<ref name="behrman-2007" />

Based on distinct clinical presentations, there are three main subgroups of preterm births: those that occur due to spontaneous premature labor, those that occur due to spontaneous membrane ([[amniotic sac]]) rupture, and those that are medically induced.<ref>{{Cite journal |last=Kramer |first=M. S. |date=October 1987 |title=Intrauterine growth and gestational duration determinants |url=https://pubmed.ncbi.nlm.nih.gov/3658568 |journal=Pediatrics |volume=80 |issue=4 |pages=502–511 |doi=10.1542/peds.80.4.502 |issn=0031-4005 |pmid=3658568 |s2cid=21632987}}</ref> Both spontaneous factors are viewed to be a result of similar causes; hence, two main classifications remain: spontaneous and medically induced causes.<ref>{{Cite journal |last=Klebanoff |first=M. A. |year=1998 |title=Conceptualizing categories of preterm birth |journal=Prenatal and Neonatal Medicine |volume=3 |issue=1 |pages=13–15}}</ref> The risk of spontaneous PTB increases with "extremes of maternal age (both young and old), short inter-pregnancy intervals, multiple gestations, assisted reproductive technology, prior PTB, family history, substance abuse, cigarette use, low maternal socioeconomic status, late or no prenatal care, low maternal prepregnancy weight, [[bacterial vaginosis]], [[periodontal disease]], and poor pregnancy weight gain."<ref>{{Cite journal |vauthors=Rubens CE, Sadovsky Y, Muglia L, Gravett MG, Lackritz E, Gravett C |date=November 2014 |title=Prevention of preterm birth: harnessing science to address the global epidemic |journal=Science Translational Medicine |volume=6 |issue=262 |pages=262sr5 |doi=10.1126/scitranslmed.3009871 |pmid=25391484 |s2cid=8162848 |doi-access=free}}</ref> Medically induced preterm birth is often conducted when continuing pregnancy poses significant risks to the pregnant parent or fetus; the most common causes include [[preeclampsia]], diabetes, maternal medical conditions, [[fetal distress]], or developmental problems.<ref name="Moutquin-2003" /> Despite these risk factors, the underlying causes of premature infant death are often unknown, and approximately 65% of all cases are not associated with any known risk factor.<ref name="harrison-2016" />

Infant mortality caused by premature birth is mainly attributed to developmental immaturity, which impacts multiple organ systems in the infant's body.<ref name="behrman-2007-2">{{Cite book |last1=Behrman |first1=Richard E. |url=https://www.ncbi.nlm.nih.gov/books/NBK11385/ |title=Mortality and Acute Complications in Preterm Infants |last2=Butler |first2=Adrienne Stith |last3=Outcomes |first3=Institute of Medicine (US) Committee on Understanding Premature Birth and Assuring Healthy |date=2007 |publisher=National Academies Press (US) |language=en}}</ref> The main body systems affected include the respiratory system, which may result in [[pulmonary hypoplasia]], [[Infant respiratory distress syndrome|respiratory distress syndrome]], [[bronchopulmonary dysplasia]] (a chronic lung disease), and [[apnea]].<ref name="behrman-2007-2" /> Other body systems that fully develop at a later gestational age include the [[Gastrointestinal tract|gastrointestinal system]], the skin, the [[immune system]], the [[cardiovascular system]], and the [[Blood|hematologic system]].<ref name="behrman-2007-2" /> Poor development of these systems increases the risk of infant mortality.{{cn|date=December 2023}}

Understanding the biological causes and predictors of PTB is important for identifying and preventing premature birth and infant mortality. While the exact mechanisms responsible for inducing premature birth are often unknown, many of the underlying risk factors are associated with inflammation. Approximately "80% of preterm births that occur at <1,000 g or at <28 to 30 weeks of gestation" have been associated with inflammation.{{citation needed|date=July 2023}} Biomarkers of inflammation, including [[C-reactive protein]], [[ferritin]], various [[interleukin]]s, [[chemokine]]s, [[cytokine]]s, [[defensin]]s, and [[bacteria]], have been shown to be associated with increased risks of infection or inflammation-related preterm birth. Biological fluids have been utilized to analyze these markers in hopes of understanding the pathology of preterm birth, but they are not always useful if not acquired at the appropriate gestational time-frame. For example, biomarkers such as [[fibronectin]] are accurate predictors of premature birth at over 24 weeks of gestation but have poor predictive values before then.<ref>{{Cite journal |vauthors=Goldenberg RL, Goepfert AR, Ramsey PS |date=May 2005 |title=Biochemical markers for the prediction of preterm birth |journal=American Journal of Obstetrics and Gynecology |volume=192 |issue=5 Suppl |pages=S36-46 |doi=10.1016/j.ajog.2005.02.015 |pmid=15891711}}</ref> Additionally, understanding the risks associated with different gestational ages is a helpful determiner of [[Gestational age-specific mortality]].<ref name="behrman-2007">{{Cite book |last1=Behrman |first1=Richard E. |url=https://www.ncbi.nlm.nih.gov/books/NBK11386/ |title=Prematurity at Birth: Determinants, Consequences, and Geographic Variation |last2=Butler |first2=Adrienne Stith |last3=Outcomes |first3=Institute of Medicine (US) Committee on Understanding Premature Birth and Assuring Healthy |date=2007 |publisher=National Academies Press (US) |language=en}}</ref>