Tocolytic Therapy for Acute Preterm Labor

Question 1

What races have higher incidence of preterm labor?

Answer 1

AA

Question 2

T or F. Women with a previous Hx of preterm labor have an increased risk of having another preterm child

Answer 2

T. Although this risk can be offset with progesterone admin

Question 3

What are the other risk factors of preterm labor?

Answer 3

low socioeconomic statue

poor nutritional status

extremes of age

smoking

Question 4

What is thought to cause preterm labor?

Answer 4

multifactorial with an underlying infection as the initiating factor in up to 40% of preterm births

Question 5

Why would an infection stimulate labor?

Answer 5

Activation of the immune system can produce inflammatory cytokines and prostaglandins that result in uterine contractions and weakening of the amniotic membranes

NOTE: ABX have NOT been shown to decrease the risk of preterm birth

Question 6

What are tocolytics used for?

Answer 6

They can temproarily inhibit uterine contractions (but have not been shown to prevent preterm labor before 37 weeks)

Question 7

What is the primary goal of tocolytic therapy?

Answer 7

to allow admin of glucocorticoids to reduce the risk of the prematurity related complications of respiratory distress syndrome, necrotizing entercolitis, and hemorrhage OR

to facilitate maternal transport to a more appropriate facility for birth

Question 8

What is the most commonly used tocolytic?

Answer 8

Magnesium sulfate

Question 9

How does magnesium sulfate prevent labor?

Answer 9

It decreases the availability of calcium by blocking intracellular channels, which decreased myometrial contractility

Question 10

What are some possible maternal AEs to magnesium sulfate?

Answer 10

flushing, N/V, blurry vision, HA, lethargy, hypotension, and pulmonary edema

Question 11

What are some signs of magnesium sulfate toxicity?

Answer 11

loss of patellar reflexes followed by decreased urine output

Respiratory depression can occur

Question 12

How would magnesium sulfate affect the neonatal heart?

Answer 12

causes non-clinically significant bradycardia

Question 13

What are some suggested protective mechanisms of magnesium sulfate?

Answer 13

-can prevent gross motor dysfunction (cerebral palsy)

Question 14

Although it is widely used as a tocolytic agent, the literature does not support MS as being effective in withholding delivery for 48 hrs, preventing preterm birth, or reducins the risk for neonatal morbidity BUT is most likely neuroprotective for the fetus

Question 15

What are some beta-mimetics used in labor delay?

Answer 15

Terbutaline, Salbutamol, and Hexoprenaline

Question 16

T or F. Beta mimetics should not be used for prolonged tocolysis (48-72+ hrs) because of the potential for serious maternal cardiac toxicity and death

Answer 16

T.

Question 17

How do beta-mimetics work?

Answer 17

They function as beta-adrenergic receptor agonists, relaxing smooth muscle including the myometrium via Gi mechanisms (cAMP) causing suppression of the availability of intracellular calcium and the activity of myosin light-chain kinases, thus suppressing myometrial contractility

Question 18

Are beta-mimetics effective?

Answer 18

They decrease the risk of delivery within 48 hrs and show a trend toward reduction within 7 days, but there is no reduction in preterm birth or neonatal morbidity.

Question 19

How do beta-mimetics compare to other tocolytics?

Answer 19

They are not superior and not as effective as nifedipine in reducing the risk of delivery within 7 days or before 34 weeks gestation

Question 20

What is the most commonly used beta-mimetic?

Answer 20

Terbutaline given as a subQ injection

Question 21

What are some AEs to beta-mimetics?

Answer 21

tachycardia, tremor, dyspnea, chest discomfort, palpitations, and hyperglycemia

Question 22

Beta-mimetics are contraindicated in what pts.?

Answer 22

those with known cardiac disease or poorly controlled diabetes

Question 23

What are calcium channel blockers most commonly used for?

Answer 23

Tx of HTN, angina, and coronary artery disease by preventing reuptake of calcium ions via voltage-dependent calcium channels

These work to prevent labor osnet because the lack of intracellular calcium inhibits actin and myosin, and thus myometrial activity

Question 24

What are the main advantages of nifedipine in preventing labor?

Answer 24

Significantly reduced risk of delivery within 7 days of initiations as well as a reduction in delivery rates before 34 weeks, as well as decreased risk of respiratory distress, necrotizing enterocolitis, and intraventricular hemorrhage

Question 25

What is the most commonly used prostaglandin inhibitor to treat preterm labor?

Answer 25

Indomethacin.

Question 26

How do prostaglandins induce labor?

Answer 26

they increase gap junction size which facilitates increased intracellular calcium leading to myometrial contractility

Question 27

T or F. Overall, studies have shown that prostaglandin inhibitors are better tolerated and have a lwoer discontinuation rate owing to side effects than other tocolytics such as beta-mimetics and magnesium sulfate

Answer 27

T.

Question 28

What effects do prostaglandin inhibitors have on the fetus?

Answer 28

Premature closure of the ductus arteriosus and oligohydramnios if used for too long

It seems to be a safe and effective tocolytic when used for a short period of time, however