Tocolytic therapy for preterm labour: assessing its potential for reducing preterm delivery

Lipoxygenase and cyclooxygenase inhibitors reveal a complementary role of arachidonic acid derivatives in pregnant human myometrium

OBJECTIVE

The aim of this study was to assess the involvement of lipoxygenase (LOX) metabolic pathways in uterine tissues from pregnant women as well as the combined inhibition of LOX and cyclooxygenase (COX) on contractile activity.

STUDY DESIGN

Uterine biopsies were performed from consenting women undergoing elective caesarean sections at term (n = 24). Western blot analysis and isometric tension measurements were performed in vitro on fresh human myometrial strips. Concentration-response curves to arachidonic acid (AA) 861 and baicalein (5- and 12-LOX inhibitors, respectively) were performed. The combined effects of baicalein and indomethacin were also assessed. Contractile activities were quantified by calculating both amplitude and the area under the curve over 20 minute periods.

RESULTS

5- and 12-LOX were present in all tested tissues. Addition of AA861 or baicalein resulted in tocolytic effects (P < .05). Finally, the combined inhibition of both COX and 12-LOX pathways resulted in additive tocolytic effects.

CONCLUSION

5- and 12-LOX pathways modulate human myometrium contractility.

The present and future of tocolysis

This chapter discusses the tocolytic agents currently in use for the treatment of preterm labour and considers them in light of the evidence base. These agents are the beta2 sympathomimetic agonists, magnesium sulphate (MgSO(4)), indomethacin, nifedipine and atosiban. The available evidence for these agents shows that the beta2 agents are effective but have significant maternal side effects and no effect on perinatal outcome. MgSO(4) and glyceryl trinitrate are clearly ineffective. Nifedipine is effective with a low maternal side effect profile and is associated with improved perinatal outcomes. Meta-analyses of the several randomized controlled trials of atosiban show that it is no more effective than other tocolytic therapies. Possible directions for the future will be discussed.

Genetic variation associated with preterm birth: a HuGE review

Preterm birth (PTB) is a major public health concern because of its high prevalence, associated mortality and morbidity, and expense from both short-term hospitalization and long-term disability. In 2002, 11.9% of U.S. births occurred before 37 weeks gestation. Epidemiologic studies have identified many demographic, behavioral, and medical characteristics associated with PTB risk. In addition, recent evidence indicates a role for genetic susceptibility. We reviewed 18 studies published before June 1, 2004, that examined associations between polymorphisms in the maternal or fetal genome and PTB risk. Studies of a polymorphism in tumor necrosis factor-alpha, a proinflammatory cytokine, showed the most consistent increase in the risk of PTB. Environmental factors such as infection, stress, and obesity, which activate inflammatory pathways, have been associated with PTB, suggesting that environmental and genetic risk factors might operate and interact through related pathways. This review highlights maternal and fetal genetic susceptibilities to PTB, the potential relationships with environmental risk factors, and the need for additional well-designed studies of this critical public health problem.

The epidemiology of threatened preterm labor: a prospective cohort study

OBJECTIVE

The purpose of this study was to describe the occurrence, timing, and outcomes of hospital-based diagnoses of preterm labor.

STUDY DESIGN

Administrative records identified hospital admissions for preterm labor among 2534 women in an ongoing cohort study. Factors that were considered risks for prematurity were examined by logistic regression for an association with any preterm labor diagnosis, a preterm labor diagnosis <33 weeks of gestation, or > or =33 weeks of gestation.

RESULTS

Of 234 women (9%) who experienced hospitalization for preterm labor, 90 women (38%) were delivered in the first episode. Previous preterm birth consistently was associated with a diagnosis of preterm labor. Reporting a sexually transmitted infection (odds ratio, 1.8; 95% CI, 1.1-3.0) or bacterial vaginosis (odds ratio, 2.6; 95% CI, 1.7-4.1) early in pregnancy was associated with hospitalization for preterm labor between 24 and 32 weeks of gestation.

CONCLUSION

The incidence of first-time hospitalization for preterm labor was 9%, with most episodes not resulting in preterm birth. Previous preterm birth was associated therefore with a preterm labor diagnosis.

What is the future of tocolysis?

Use of the currently available tocolytics is controversial because it has not been associated with improved perinatal outcomes. New markers of preterm labour may come from gene-profiling studies, in as much as they may help in identifying novel genes regulating myometrial quiescence and in expanding our understanding of the pathologic process of uterine dysfunction. Study of certain transcripts in circulating white blood cells by RT-PCR could assist the obstetrician in evaluation of the risks. Uterine electromyography (EMG) also has the potential benefit of monitoring tocolytic treatment, although no standard method of clinical interpretation has yet been devised for the results yielded by this instrumentation. Recent functional genomic studies found that in the uterus at term there is a massive down-regulation of a large panel of developmental cell adhesion molecules and proliferation-related genes. Conversely, maintaining the developmental processes in an active state in patients at risk would help to prevent preterm delivery. It is too early to suggest any therapies with anticytokines in pregnant women. However, exploration of genetic polymorphisms, which may influence the balance of pro- and anti-inflammatory cytokines that are relevant to the course of preterm labour, seems to be a novel avenue that should be explored.