Search for best tocolytic for preterm labour

Comparing forces on the fetal neck in breech delivery in lithotomy versus all-fours position: a simulation model

PURPOSE

To measure forces applied to the fetal neck, in a simulation model for breech delivery, in both lithotomy versus all-fours position.

METHODS

We used a Laerdal SimMom simulator and a Birthing Baby together with PROMPT Flex Software. The descent of the fetus was accomplished using the Automatic Delivery Module 2. The baby was always in breech position; the SimMom in either all-fours or lithotomy positions. Sensors were located inside the fetal neck region to simulate forces applied to the plexus.

RESULTS

The lowest force on the fetal neck region was recorded for the delivery in all-fours position without further maneuvers (mean force 58.70 Newton, standard deviation 2.54 N). As weight was added to the baby, the force increased (i.e. + 500 g, mean force 71.8 N, SD 3.08 N, p < 0.001). Delivery in lithotomy position resulted in a mean force of 81.56 N (SD 19.55 N). The force significantly increased in case of delivery of the head without assistance from contractions (mean force 127.93 N, SD 23.10 N). In all-fours position, the delivery of the fetal head from pelvic floor level without contractions (Frank's Nudge maneuver) resulted in a mean force of 118.45 N (SD 15.48 N, p = 0.02). Maneuvers for shoulder dystocia (the inverted type that can occur during breech delivery) led to significantly higher mean forces independent from birthing positions.

CONCLUSION

Breech delivery in all-fours position was associated with the lowest force acting on the fetal neck in our simulation model.

Hypotension in normotensive pregnant women treated with nifedipine as a tocolytic drug

OBJECTIVE

To determine hypotensive effect of nifedipine in the treatment of preterm labor.

METHODS

A descriptive analytic study was conducted on pregnant women treated with nifedipine as tocolytic drug for preterm labor. Maternal blood pressure before and at 15, 30, 45 and 60 min after administration of nifedipine was evaluated and analyzed. Hypotension was defined as a decrease in systolic or diastolic blood pressure of 15 mmHg or more.

RESULTS

A total of 157 pregnant women met the inclusion criteria. The mean systolic and diastolic blood pressure before treatment was 109.4 and 72.5 mmHg, respectively. The blood pressure following treatment with nifedipine was significantly decreased both systolic and diastolic blood pressure (p < 0.05) at 30, 45 and 60 min. Of 157 patients, 28 (17.8%) and 27 (17.2%) had systolic and diastolic hypotension, respectively. Of the patients with decreased blood pressure, the mean decrease of systolic and diastolic blood pressure was 16.3 and 14.5 mmHg, respectively.

CONCLUSION

Nifedipine was associated with a minimal but significant decrease in blood pressure. 17% of cases have hypotension. However, hypotension secondary to nifedipine was not associated with significant clinical symptoms, suggesting that nifedipine is relatively safe in terms of hypotensive effect.

Differences in muscarinic-receptor agonist-, oxytocin-, and prostaglandin-induced uterine contractions

OBJECTIVE

To investigate the contractile response of the perfused swine uterus to various receptor pathways (oxytocin, prostaglandins, and muscarine).

DESIGN

An extracorporeal perfusion model of the swine uterus was used that keeps the uterus in a functional condition and is appropriate for the study of physiologic questions.

INTERVENTION(S)

Oxytocin-, prostaglandin-, and carbachol-induced uterine contractility and peristalsis were assessed using an intrauterine double-chip microcatheter.

SETTING

University hospital.

MAIN OUTCOME MEASURE(S)

Intrauterine pressure profiles.

RESULT(S)

A dose-dependent increase in intrauterine pressure (IUP) in the isthmus uteri and corpus uteri was observed after the administration of prostaglandin F(2alpha) (PGF(2alpha)) and oxytocin, which reached a plateau after further stimulation. A dose-dependent increase in IUP in the isthmus uteri and corpus uteri was also observed after the administration of prostaglandin E(1) (PGE(1)) and prostaglandin E(2) (PGE(2)), with a plateau in IUP in the middle-concentration range and a decrease during the further course of stimulation. After administration of PGE(1), PGE(2), and PGF(2alpha), different directions of contraction waves were also observed. Carbachol also showed a unique contractility pattern, with isolated, very powerful, dose-dependent contractions with an IUP gradient, suggesting directed transport from the upper region to the lower region.

CONCLUSION(S)

This study demonstrated that oxytocin, the prostaglandins, and carbachol modulate contractility in nonpregnant swine uteri in a characteristic way, resulting in different contractility patterns.

Guidelines for the management of spontaneous preterm labor

Preterm birth is defined as delivery at <37 completed weeks of pregnancy (World Health Organization). Spontaneous preterm birth (SPB) includes preterm labor, preterm spontaneous rupture of membranes, preterm premature rupture of membranes (PPROM) and cervical weakness; it does not include indicated preterm delivery for maternal or fetal conditions. Early SPB (<32 weeks' gestation) is associated with an increased higher perinatal mortality rate, inversely proportional to gestational age. The pathophysiologic events that trigger SPB are largely unknown but include decidual hemorrhage (abruption), mechanical factors (uterine overdistention or cervical incompetence), and hormonal changes (perhaps mediated by fetal or maternal stress). In addition, several cervicovaginal infections have been associated with preterm labor. SPB is also the leading cause of long-term morbidity, including neurodevelopmental handicap, cerebral palsy, seizure disorders, blindness, deafness and non-neurological disorders, such as bronchopulmonary dysplasia and retinopathy of prematurity. Delaying delivery may reduce the rate of long-term morbidity by facilitating the maturation of developing organs and systems. The benefits of administration of antepartum glucocorticosteroids to reduce the incidence and severity of respiratory distress syndrome may be exploited by delay. Delay may also permit transfer of the fetus in utero to a center with neonatal intensive care unit facilities. There is considerable variation in the way that spontaneous preterm labor (SPTL) is diagnosed, managed and treated internationally. The development of clinical guidelines requires an evidence-based approach to improve outcome and allow more efficient use of resources. With recent advances in our understanding of the etiology and mechanisms of SPTL and the availability of safer, more specific tocolytics, it was felt that guidelines should be developed to achieve, if possible, an European consensus in patient diagnosis, management and treatment.

Randomized double-blind placebo-controlled trial of transdermal nitroglycerin for preterm labor

OBJECTIVE

Despite advances in perinatal medicine, the incidence of preterm birth continues to increase. The primary goal of tocolytic therapy is to reduce neonatal morbidity and mortality. While studies have demonstrated a prolongation of pregnancy, no tocolytic has been shown to improve neonatal outcomes. The objective of this randomized placebo-controlled trial was to determine the effect of transdermal nitroglycerin on neonatal outcomes in women who present in preterm labor.

STUDY DESIGN

We randomized 153 women in labor between 24 and 32 weeks to receive either transdermal nitroglycerin or placebo patches. The primary outcome was a composite of neonatal morbidity (chronic lung disease, intraventricular hemorrhage, periventricular leukomalacia, necrotizing enterocolitis) and mortality. Secondary outcomes included birth within 48 hours, birth before 28, 34, and 37 weeks, number of doses of antenatal corticosteroids received, side effects, and adverse events.

RESULTS

Infants born to transdermal nitroglycerin treated mothers (n = 74) had a statistically significantly reduced composite outcome compared to placebo treated mothers (n = 79) (relative risk 0.29 [95% confidence interval 0.08, 1.00] [p = 0.048]; risk difference -0.10 [95% confidence interval -0.19, -0.01); number needed to treat 10 [95% confidence interval 5, 100]). Birth prior to 28 weeks was reduced (relative risk 0.50, 95% confidence interval 0.23, 1.09). Transdermal nitroglycerin caused significantly more maternal side effects (relative risk 1.41, 95% confidence interval 1.06, 1.86).

CONCLUSION

Transdermal nitroglycerin may reduce neonatal morbidity and mortality as a result of decreased risk of birth before 28 weeks.

Uterine contractility in response to different prostaglandins: results from extracorporeally perfused non-pregnant swine uteri

BACKGROUND

Prostaglandins (PGs) are important stimulators of uterine contractility. Limited data are available at present on the effects of different PGs on uterine contractility, measured using intraluminal pressure changes in the complete uterus. The goal of this study was to assess dynamic changes in uterine contractility and peristalsis in response to PGs in comparison with the effects of oxytocin administration.

METHODS

An extracorporeal perfusion model of swine uteri was used, which keeps the uterus in a functional condition, and is appropriate for the study of physiological questions. Oxytocin- and PG-induced uterine contractility and peristalsis were assessed using an intrauterine double-chip microcatheter.

RESULTS

A dose-dependent increase in intrauterine pressure (IUP) in the isthmus uteri (P < 0.001) and the corpus uteri (P < 0.001) was observed after the administration of PGF(2alpha) and oxytocin, which reached a plateau after further stimulation. A dose-dependent increase in IUP in the isthmus uteri (P < 0.001) and the corpus uteri (P < 0.001) was also observed after the administration of PGE(1) and PGE(2), with a plateau in IUP in the middle-concentration range and a decrease in the course of further stimulation. PGE(2) caused significantly more contractions starting in the corpus uteri and moving to the isthmus uteri (P = 0.008). The direction of most contractions caused by PGE(1), PGE(2) and oxytocin differed from that of PGF(2alpha).

CONCLUSIONS

This study demonstrates that the PGs tested modulate contractility in non-pregnant swine uteri in a characteristic way, resulting in different contractility patterns.

Risk-benefit effects of tocolytic therapy

Tocolytics are potent drugs that are used to interdict preterm labour. Although all of these agents have some side effects, if not frankly adverse effects under certain clinical situations, two of these drugs, the beta-mimetics and magnesium sulphate (MgSO(4)), have been found to have considerable potential for adverse maternal cardiovascular and respiratory effects. Furthermore, magnesium sulphate has been shown to have harmful, indeed, sometimes lethal, effects in some babies. Although less well established, NSAIDs, the most common example of which is indomethacin, also have some important adverse effects in fetuses. Within the limits of contemporary scientific knowledge, calcium channel blockers, such as nifedipine, appear to be among the more efficacious and safer drugs that are currently being used for tocolysis.

Delay of preterm birth in sheep by THG113.31, a prostaglandin F2alpha receptor antagonist

OBJECTIVE

A novel prostaglandin F2alpha receptor antagonist, THG113.31, was tested for the suppression of uterine contractility and delay of preterm labor in sheep.

STUDY DESIGN

We determined the tocolytic effectiveness of THG113.31 on contractions that were stimulated in vitro by prostaglandin F2alpha and E2 in longitudinal and circular myometrial strips. We also tested the ability of THG113.31 in vivo to lower uterine electromyographic activity that was induced by the progesterone receptor blocker, RU486, and to delay preterm birth.

RESULTS

THG113.31 suppressed the amplitude of prostaglandin F2alpha, but not prostaglandin E2-induced contractions of both circular and longitudinal myometrium (P<.01). The times to delivery after RU486 were 34.8+/-1.1 hours (saline solution) and 41.9+/-0.5 hours (THG113.31; P<.001) or an average delay of 7.1 hours. There were no changes in fetal blood gases (PaO2 , PaCO2 , pH, or SaO2) because of THG113.31. Fetal cortisol levels rose in each group, and fetal and maternal prostaglandin E2 and F2alpha metabolite concentrations rose similarly in both groups.

CONCLUSION

THG113.31 specifically suppresses prostaglandin F2alpha-induced myometrial contractility and delays delivery.

Current medical therapy in the prevention and treatment of preterm labour

The prevention of preterm birth should be one of the major aims of antenatal care. Unfortunately, identification of women who will subsequently deliver preterm is imprecise. Prevention is also difficult. Surgical prevention with cerclage may help a proportion of women. Medical prevention is currently limited to the identification and treatment of bacterial vaginosis, although recent studies have suggested that progesterone prophylaxis may be helpful in some women. Confirmation of efficacy and safety is required before progesterone is introduced as long-term prophylaxis for all women at high risk. The optimal medical treatment (rather than prevention) of threatened preterm labour is controversial. Tocolysis is generally accepted to improve neonatal outcome although this has never been convincingly demonstrated in appropriate trials. Antibiotics confer benefit in the presence of ruptured membranes but are not indicated in uncomplicated preterm labour. In future, it may be possible to identify a subgroup of women in preterm labour with intact membranes who will benefit from tocolysis. The choice of first-line tocolytic therapy is currently debated but atosiban or nifedipine are suggested in current UK guidelines. A direct comparison of these drugs is required in a clinical trial. Although indirect comparisons have been made, these are difficult to interpret due to methodological differences. Each of these drugs have their advocates. Nifedipine has been reported to delay delivery and improve outcome but there are inconsistencies in the clinical trials. Atosiban is also reported to delay delivery and is well tolerated but improved neonatal outcome may have been hidden in clinical trials due to the requirement for rescue tocolysis.

Adverse and beneficial effects of tocolytic therapy

In addition to questions raised about the efficacy of many tocolytics, appropriate concern has been voiced about the safety of these potent drugs. Although some degree of risk for adverse effects with drugs promising a strong therapeutic effect can be accepted, caution needs to be exercised when benefits are marginal or unproven. Unfortunately, some of the tocolytics, most notably the betamimetics and magnesium sulfate, have been found to have considerable potential for adverse maternal cardiovascular and respiratory effects. Although less clearly established, the use of indomethacin appears to be associated with increased fetal and neonatal risks. Concerning magnesium sulfate, in addition to the well-known maternal effects, the accumulating evidence showing an increased frequency of adverse outcomes in the fetus and neonate has led to the recommendations to abandon its use entirely as a tocolytic. Given the limitations of our current state of knowledge, nifedipine would appear to be among the more efficacious and safer tocolytics available to use when properly indicated.

Medical and obstetric problems complicating pregnancy

The present review addresses several medical and obstetric factors/problems, and their interactions during pregnancy. These include the following: maternal age; morbidity and mortality during pregnancy; thromboembolism; gestational diabetes; haemolysis, elevated liver enzymes, low platelets syndrome; human immunodeficiency virus; hepatitis C; preterm labour; antenatal administration of corticosteroids; intrapartum surveillance; breech delivery; and caesarean section.