Premature birth, defined as birth before 37 weeks of gestation, is a leading cause of infant morbidity and mortality. In the United States, approximately 1 in 10 infants is born prematurely. Premature birth can lead to both short-term and long-term health complications, including respiratory distress, intraventricular hemorrhage, necrotizing enterocolitis, and developmental delays. Understanding the causes of premature birth is critical for developing preventative strategies.
There are 4 main categories of factors that can cause premature birth:
Maternal factors
Certain maternal health conditions and behaviors increase the risk of preterm delivery. The most significant maternal risk factors include:
- Having a previous preterm birth
- Short interval between pregnancies (less than 6-12 months between birth and conception of next pregnancy)
- Chronic conditions like diabetes, high blood pressure, clotting disorders
- Infections – urinary tract, sexually transmitted diseases, malaria
- Lifestyle factors like smoking, substance abuse, inadequate prenatal care
- Multiple pregnancies (twins, triplets)
- Abnormalities with uterus, cervix or placenta
- Older maternal age (over 35 years old)
- Younger maternal age (teen pregnancies)
Women with a history of preterm delivery are at highest risk for preterm birth in subsequent pregnancies. Inter-pregnancy interval is also critical – getting pregnant within 6 months of a previous birth increases risk. Chronic maternal health conditions like diabetes, hypertension, blood clotting disorders increase risk through placental abnormalities and disease. Infections during pregnancy can directly stimulate preterm contractions and labor. Lifestyle factors like smoking, substance abuse, and inadequate prenatal care all confers risk through multiple mechanisms (impaired placental function, greater susceptibility to infections, direct toxicity to the fetus).
Fetal factors
Certain fetal conditions also increase risk of premature delivery. These include:
- Multiple fetuses (twins, triplets)
- Abnormalities of the placenta or umbilical cord
- Birth defects
- Intrauterine growth restriction
- Fetal infection
- Fetal distress
The most significant fetal risk factor is multiple fetuses – almost 60% of twins are born prematurely. The presence of two or more fetuses increases demands on the placenta and uterus, resulting in earlier labor onset. Placental and umbilical cord abnormalities like placenta previa and vasa previa can cause bleeding and early delivery. Some birth defects, like congenital heart disease, are associated with preterm birth. Babies that show intrauterine growth restriction are often delivered early due to inadequate growth. Fetal infections, like cytomegalovirus or rubella, can also lead to early delivery. Finally, signs of fetal distress, like abnormal heart rhythms, may prompt earlier delivery.
Environmental factors
A variety of environmental exposures have been linked to higher risk of preterm birth. Some key risks include:
- Air pollution
- Heavy metal exposure
- Pesticides
- Phthalates (chemicals in plastics)
- Vitamin D deficiency
- Periodontal disease
- Physical injury or trauma
Exposure to air pollution and heavy metals is associated with oxidative stress and inflammation, which may trigger early labor. Pesticides and phthalates can disrupt normal hormonal processes necessary for maintaining pregnancy. Low vitamin D levels may increase risk of infection and inflammation. Periodontal disease increases systemic inflammation, which again can cause premature contractions. Physical trauma, like a car accident, can directly trigger preterm birth through placental abruption or rupture of membranes.
Iatrogenic factors
Finally, premature birth can also be caused by medical interventions, known as iatrogenic factors. These include:
- Labor induction
- Cesarean delivery
- Cervical procedures like cone biopsy
- Fertility treatments
Induction of labor and cesarean deliveries are sometimes performed for maternal-fetal indications prior to 37 weeks, leading to iatrogenic prematurity. Procedures on the cervix, like Loop Electrosurgical Excision Procedure (LEEP), can increase risk in subsequent pregnancies. Fertility treatments, especially multiple embryo transfers during IVF, greatly increase risk of multiples and preterm birth.
Conclusion
Premature birth has numerous causes, ranging from pre-existing maternal health problems to environmental exposures and medical interventions. However, the four major categories of risk factors are maternal factors like chronic disease and infection, fetal factors like multiple gestation pregnancies, environmental toxins like air pollution, and iatrogenic causes like elective early delivery. A combination of genetic risks, individual health status, and environmental exposures interacts to initiate labor prematurely in susceptible women. Understanding the complex web of causes that leads to preterm birth is essential for developing preventative strategies to reduce global rates of prematurity.
References
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