Preterm Labor Day: Factors Associated with Preterm Birth

Labor Day weekend always seems to be busy for us. I think pregnant women believe it represents a celebration and expectation of delivery rather than a tribute to the average working person. And, each year I always seem to be on call to help them celebrate, I suppose as the representative of the typical working person who NEVER gets Labor Day off! This Labor Day was no different and it provided appropriate fodder for my next promised post on preterm birth (PTB): one woman with triplets and spontaneous rupture of membranes at 28 weeks’; one with placenta previa (placenta covering the cervix) and bleeding, accompanied by uterine infection, at 32 weeks; one with a history of a D&C following spontaneous abortion of her previous pregnancy who came in with premature labor at 23 weeks; and, one who delivered a 36 week baby by cesarean section for breech presentation at an outside hospital that required transfer to our neonatal intensive care unit because of respiratory distress.

These four women illustrate several of the major risk factors associated with preterm birth: multifetal pregnancy; placental abnormalities leading to midtrimester bleeding, accompanied over time by infection; possible cervical abnormality (cervical incompetence) resulting from a previous surgical procedure; and “iatrogenic prematurity” resulting from a complacent attitude toward delivery in late third trimester. (The latter is scheduled for a separate post because it is a growing problem in this country that needs to be aggressively addressed).

There are many other risk factors for PTB, for example, black race, maternal age less than 17 or greater than 35, low socioeconomic status, genitourinary tract infections, uterine abnormalities, substance abuse of any kind (tobacco, alcohol, illicit drugs), major stress, low maternal weight, obesity, lack of social supports, poor oral hygiene, to name just a few. But, one of the most important is a history of previous preterm labor or delivery or prior low birthweight baby. A woman who has one preterm delivery has a 15-20% chance of a second; and, if she has two consecutive PTBs, the risk of recurrence ranges between 30-50%! The earlier the previous PTB, the more likely there will be a recurrence. Interestingly, women who have a history of infertility are also at greater risk for PTB once they conceive.

About 40% of PTBs follow “spontaneous preterm labor,” 30% follow premature rupture of membranes, and 30% are “iatrogenic,”resulting from indicated early delivery for maternal or fetal complications, miscalculation of gestational age, or unrealistic expectations of fetal “maturity” in late third trimester (“late preterm” or “near term” births). Spontaneous PTB after 32 weeks is more often associated with increased frequency of uterine contractions, increased uterine volume secondary to multiple gestation or excess amniotic fluid (polyhydramnios), and less likely to be complicated by infection. Early preterm birth (less than 32 weeks) is often associated with infection (overt or subclinical), more frequently associated with long-term morbidity for the baby, and more likely to recur in a subsequent pregnancy. For reasons that are not well understood, it is also more common in African-Americans.

In my next post, I will explain my concerns related to "late preterm birth." Until then, see ya later....

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