The Role of the Vaginal Microbiome in Preterm Birth

Introduction: Preterm birth

Preterm birth (PTB) is the delivery of newborns before the 37th week of gestation, with most preterm births (>80%) occurring between 32 and 37 weeks 15. Globally, rates of preterm birth range from 5-18% for 184 countries, amounting to 15 million babies born prematurely each year 15. In America, preterm birth accounts for 11-12% of American pregnancies 3,9 but with marked disparities in race, occurring in 17.8% of births in African Americans. 3 Both the rates for the United States and the world have been increasing for the past several decades 15, 3, 2. In the United States, incidence of preterm birth increased 30% from 1981 to 2010 15.

Causes of Preterm Birth

There are two main types of preterm labor: providor-initiated birth, involving elective Cesarean section or induction of labor before term, and spontaneous. The majority (70–75%) of all preterm births are spontaneous 1. Prior to about 30% of sPTBs, the fetal membranes rupture, known as preterm prelabor rupture of membranes (PPROM)14.

The causes and mechanisms of spontaneous PTB are not fully understood; In as many as half of all spontaneous preterm births, the cause remains unknown. Many risk factors have been identified, preterm birth is likely caused by an interplay of them 15.

Some risk factors include environmental effects such as exposure to air pollution 16, and identity factors including ethnicity, education level 1, socioeconomic status, and maternal age (those younger than 18 or older than 35 have higher risk). Maternal health is very important, with inadequate nutrition 17, and unhealthy Western-style diets 18, low or high Body Mass Index (BMI), diabetes, chronic hypertension, metabolic and genetic disorders, and other underlying diseases increasing risk of preterm birth 10. Lifestyle risk factors include excessive physical work or long times spent standing, stress, smoking, alcohol, and drug use during pregnancy, 15. Additionally, factors relating to the pregnancy, including inadequate prenatal care, multiple gestations (twins, triplets, ect), primiparity (the number of offspring female has borne), and short intervals of time between pregnancies, increase risk of preterm birth 1, 10.

[ Some Factors Associated with Preterm Birth, CDC]

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Effects of Preterm Birth

The effects of preterm birth are wide-ranging. Babies born prematurely have much higher incidence of disease and death, especially in the month following birth, known as the neonatal period 1. Preterm birth directly causes 35% of all neonatal deaths 15. One reason for this is that babies born before term usually do not have fully developed hearts or lungs, resulting in respiratory and cardiovascular complications that often lead to death 1. Preterm birth also indirectly increases risk of death from other factors, especially infection 15. Collectively, preterm birth is the leading cause of neonatal death 9, contributing to around 80% of perinatal mortality 10.

Even if the baby survives the first month, it will likely face many challenges. 50% of neurologic problems reported in this period can be traced to preterm birth 10. Furthermore, complications, including difficulty gaining weight in infancy 15, and aforementioned respiratory and cardiovascular disorders, continue to lead to mortality in early childhood. Worldwide, complications from preterm birth remain the leading cause of death for children under five,14 amounting to over 1 million deaths a year 15.

Those that survive into adulthood can suffer many significant, long-term impacts, including neuro-developmental and behavioral effects such as anxiety, depression, ADHD, executive functioning disorders, dyslexia, learning disabilities, cerebral palsy, and motor and sensory deficits. Hearing impairment and visual impairment including blindness, myopia, and hypermetropia are also frequent, as well as accelerated adolescent weight gain. Cardiovascular and Respiratory disorders can continue to cause problems, including increased blood pressure and chronic lung disease sometimes leading to a requirement for home oxygen 14, 15.

These effects can all have emotional and economic impacts on the family 15, as well as leading to significant socioeconomic loss later in life 1. In addition to socioeconomic loss for individuals, preterm birth incurs high societal costs, estimated at $26.2 billion yearly 2, 3, 15.

==Vaginal Microbiome== Include some current research, with at least one image.

Role of the Vaginal Microbiome in Preterm Birth

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Edited by [Elianajoy Volin], student of Joan Slonczewski for BIOL 116 Information in Living Systems, 2022, Kenyon College.