Preterm Labor and Delivery (PTL and PTD)
Definition
Preterm labor= regular uterine contractions accompanied by a change in cervical dilation, effacement, or both or initial presentation with regular contractions and cervical dilation of at least 2 cm.
Preterm birth is defined as birth between 20 0/7 weeks of gestation and 36 6/7 weeks of gestation.
Preterm labor is not the only cause of preterm birth. Sometimes membranes have ruptured or medical conditions necessitate delivery.
Statistics
12% of all live births in the US are preterm. PTL preceded approximately 50% of these.
PTD is the leading cause of neonatal mortality in the United States.
PTD account for approximately 70% of neonatal deaths and 36% of infant deaths as well as 25–50% of cases of long-term neurologic impairment in children. Children who are born prematurely have a higher risk of learning disabilities and behavioral problems. (Mayo clinic.org)
The risk of poor birth outcome generally decreases with advancing gestational age.
Infants born prematurely have increased risks of mortality and morbidity throughout childhood, especially during the first year of life.
Causes and Risk factors
It is important to note that causes and risk factors are not the same thing. The cause of a phenomenon like preterm labor implies that it is the causation, or reason that the preterm labor happened. Causation implies a direct link between one factor and one effect. For example, rupture of membranes is a cause of preterm labor.
Risk factors on the other hand may represent mere associations. For example, preterm labor is associated with teen pregnancy. However, and this is not clear, it may not be the teen age, per se, that causes the preterm labor. It might be the poor care teenagers often take of themselves that is the real cause. So while we can see the association between teen age and preterm labor, we do not necessarily see the causation.
Risk factors for Preterm Labor:
Prior preterm birth, which nearly doubles risk in a subsequent pregnancy.
Short cervical length measured by transvaginal ultra- sonography. Short cervix is been defined as less than 25 mm less than 25 weeks of gestation. The shorter the cervix, the higher the risk.
Vaginal bleeding
Urinary tract infections (UTIs)
Genital tract infections
Periodontal disease
Behavioral risk factors for preterm birth:
Low maternal pre pregnancy weight (BMI<19.8)
Smoking and other substance abuse
Short interpregnancy interval
It is interesting to note that while these are well established risk factors for preterm labor, studies have not been able to show that intervening during pregnancy on these factors has decreased the incidence of preterm labor. This is true for all the factors except one: smoking. When smoking is stopped, statistical risk of preterm labor goes down. Personally, I think that studies fail to show benefit from addressing these factors since the factors are addressed too little and too late.
Evaluation of preterm labor
Medical history, with attention to any intercurrent symptoms, details of previous pregnancies and risk factors for preterm labor
Physical exam
Lab studies to see if there are intercurrent illnesses like urinary tract infection which could be treated
Transvaginal cervical ultrasound to check cervical length
Obstetric Ultrasound to determine characteristics of the baby, fluid and placenta
External fetal monitoring and toco to evaluate the fetal heart rate and any contractions.
Prevention of Preterm Birth
Cerclage and progesterone are the two interventions that have been evaluated in randomized trials for effectiveness in preventing preterm birth in women with single gestations without a prior preterm birth .
For those with prior preterm birth:
1. IM progesterone supplementation starting at 16–24 weeks of gestation through 37 weeks to reduce the risk of recurrent spontaneous preterm birth
2. Patients who also have short cervical length (less than 25 mm) before 24 weeks of gestation, cerclage placement is effective and should be discussed.
For those without prior history of preterm birth with an incidentally identified very short cervical length less than or equal to 20 mm before or at 24 weeks:
1. Vaginal progesterone is recommended
2. cerclage placement in women with a cervical length less than 25 mm detected between 16 weeks of gestation and 24 weeks of gestation has NOT been associated with a significant reduction in preterm birth.
Management of preterm labor
The history of treating preterm labor has been characterized by our impression that we were using effective treatments, only to discover that in studies, these same treatments made no difference in the measured outcomes. Of course, the effectiveness of the treatment according to the study depends on the outcomes measured in the study. .
We have used various nonpharmacologic and pharmacologic (drug) methods to try to treat preterm labor. However, sometimes it is difficult to know if these measures are helping the preterm labor, or helping something else, or helping nothing. Sometimes it is unclear whether we are treating preterm labor itself or factors that have led to preterm labor such as dehydration or overactivity.
Bedrest, pelvic rest, and hydration have been used to treat preterm labor. According to ACOG, " Evidence for the effectiveness of these interventions is lacking, and adverse effects have been reported " . To say that evidence is lacking on the effectiveness of an intervention is different than saying that evidence shows that it does not work. In medicine, when we say we have " evidence " it must be of very high quality, from prospectively controlled blinded if possible, randomized adequately powered studies. These are cumbersome and expensive to arrange. We can state that our available evidence does not support the use of these nonpharmacologic measures, but at the same time it is still reasonable to put some of them into judicious use. It is common sense for example, to hydrate a dehydrated pregnant patient who may be suffering from the flu, which has in turn, precipitated preterm labor.
We have also used medical therapies for preterm labor such as various tocolytics drugs to inhibit uterine contractions, for example, magnesium sulfate, terbutaline, procardia and indomethacin. These tocolytic drugs DO slow contractions and prolong pregnancy. They buy time for us to administer two PROVEN therapies : corticosteroids for accelerating lung maturity, and magnesium sulfate, for protecting the premature brain. Why don't we just keep patients on these drug to keep the contractions away ? We don't because ACOG states what the best available studies have shown,
" Maintenance therapy with tocolytics is ineffective for preventing preterm birth and improving neonatal outcomes and is not recommended for this purpose."
In summary, our treatments for Preterm Labor are few and specific :
Treat intercurrent illness that may be contributing.
For PTL less than 34 weeks, use tocolytics to obtain time to administer a full course of steroids for the lungs (48 hours).
For PTL less than 34 weeks, whose first steroid dose is over week away, a repeat course of steroids may be administered.
For PTL less than 32 week, use Magnesium sulfate to protect the premature brain.
ACOG handout for patients on Preterm Labor
References:
ACOG practice bulletin number 127, June 2012 Management of Preterm Labor
ACOG practice bulletin number 130, October 2012 Prediction and Prevention of Preterm Birth