There are many causes of prematurity; some are known and some are not. Known risk factors account for about half of the cases of preterm delivery. These known risk factors include:
Urinary tract infections, respiratory illnesses, and vaginal infections are known to be associated with preterm birth. Recently, gum disease and undetected viral illnesses have been associated with increased rates of prematurity. Even if there is no known infection at the time of a preterm birth, the placenta may show signs of infection.
Group B streptococcus bacteria, in particular, are linked to preterm birth even without causing any disease in the mother. That's why there's a test for this infection, using cultures or rapid screening on swabs of the mom's genital and rectal areas. If identified, this infection can be treated with antibiotics before or during labor to prevent the spread of infection to the infant. With the onset of preterm labor, infection is presumed to be a factor, so after birth, mom and baby are treated with antibiotics.
The membranes surrounding the baby in the womb are a major barrier to infection. If these break or rupture early, the baby is at risk for infection. This is called premature rupture of membranes. If any sign of infection occurs in the mom or is suggested in the monitoring of the fetus, an early delivery will be needed. It could be that the premature rupture of membranes may be caused by infection.
Twins, triplets, and other multiples are not often carried to full term
. Twins have a 25 to 50 percent chance of an early arrival, and the odds rise from there as the number of babies carried in the uterus increases. The uterus may get tight and begin contracting, the placental blood flow may decrease, or the placenta(s) may wear out. For any of these reasons, multiples often come early, or a decision is made to deliver them early.
Infants with irregularities in development may start knocking at the door early. Ultrasound testing often helps to identify them. If the baby needs an intervention before the due date, a premature delivery may be planned.
A condition of the mother:
Moms with uterine or cervical abnormalities; chronic illnesses such as kidney disease, preeclampsia/eclampsia (a pregnancy-related illness with high blood pressure), or diabetes; or a poorly functioning, bleeding, or damaged placenta usually require early delivery of the baby. Delivery may be by cesarean section
(c-section) or a vaginal birth
may be induced for the well-being of the mother and/or the baby.
Other health factors of the mother have been linked to a higher rate of preterm birth. These include:
• A previous preterm delivery
• Fertility problems, a second trimester abortion, or miscarriage
• Becoming pregnant six weeks or less after a previous birth
• Being underweight at conception or gaining less than 20 pounds during pregnancy
• Being younger than 17 or older than 35
• Working late into pregnancy, performing heavy labor, or being subject to a lot of physical or emotional stress
• Smoking, or using drugs such as cocaine or amphetamines