The rate of rise of corticotrophin releasing factor and endogenous digoxin-like immunoreactivity in normal and abnormal pregnancy

Preeclampsia. Part 2: experimental and genetic considerations

Preeclampsia-eclampsia is still one of the leading causes of maternal and fetal morbidity and mortality. Despite active research for many years, the etiology of this disorder exclusive to human pregnancy is an enigma. Recent evidence suggests there may be several underlying causes or predispositions leading to the signs of hypertension, proteinuria, and edema, findings that allow us to make the diagnosis of the "syndrome" of preeclampsia. Despite improved prenatal care, severe preeclampsia and eclampsia still occur. Although understanding of the pathophysiology of these disorders has improved, treatment has not changed significantly in over 50 years. Although postponement of delivery in selected women with severe preeclampsia improves fetal outcome to a degree, this is not done without risk to the mother. In the United States, magnesium sulfate and hydralazine are the most commonly used medications for seizure prophylaxis and hypertension in the intrapartum period. The search for the underlying cause of this disorder and for a clinical marker to predict those women who will develop preeclampsia-eclampsia is ongoing, with its prevention the ultimate goal. This review began with the clinical and pathophysiologic aspects of preeclampsia-eclampsia (Part 1). Now, in Part 2, the experimental observations, the search for predictive factors, and the genetics of this disorder are reviewed.

Maternal plasma corticotropin-releasing hormone trajectories vary depending on the cause of preterm delivery

OBJECTIVE

Although second trimester maternal plasma corticotropin-releasing hormone concentrations are elevated in women who are destined to deliver preterm, the sensitivity and positive predictive value of an individual test of corticotropin-releasing hormone concentration is low. This poor screening performance may be due in part to the observation that the causes of preterm delivery are heterogenous, with potentially different effects on corticotropin-releasing hormone production. We have reanalyzed data from a previous cohort of women with multiple samplings to determine whether the trajectory of increase of placental corticotropin-releasing hormone provided more information than did a single sample.

STUDY DESIGN

In this cohort, where 2 to 4 samples that had been assayed for corticotropin-releasing hormone were available on 305 women, the general form of the exponential equation y = ae(bt) was fitted to the corticotropin-releasing hormone data of each individual by the Gauss-Newton nonlinear least squares method, which generated the parameters, y-intercept and rate of rise, in corticotropin-releasing hormone concentration for each woman. Nonparametric statistical techniques, including bootstrapping, were applied to compare the results for the group of women who delivered at term with the group of women who delivered spontaneously preterm and the group of women who were delivered preterm by induction or cesarean delivery because of obstetric indication.

RESULTS

The 3 clinically defined groups have significantly different parameters, y-intercept and rate of rise, which describe the corticotropin-releasing hormone trajectory. The group that delivered preterm because of obstetric indications had a similar mean y-intercept but significantly greater mean rate of rise in corticotropin-releasing hormone concentration than the term group (0.3491 vs 0.1788; 95% CI, 0.2331-0.4615 vs 0.1394-0.2330). The group that delivered spontaneously preterm had a significantly greater mean y-intercept than the group that delivered preterm because of obstetric indication (17.08 vs 1.83; 95% CI, 5.89-28.43 vs 0.03-5.19) but a similar mean rate of rise to the group that delivered at term.

CONCLUSION

These data suggest that spontaneous preterm delivery is associated with an abnormal setting of the production of corticotropin-releasing hormone that is present from very early in pregnancy, although women who experience an induced preterm delivery are characterized by rapidly rising placental corticotropin-releasing hormone concentrations. These data further suggest that clinical abnormalities that are associated with preterm delivery by induction or cesarean delivery are associated with abnormalities that lead to a rapidly increasing corticotropin-releasing hormone concentrations. Trajectories for corticotropin-releasing hormone provide information beyond that obtained from a single sample.

Rate of rise in maternal plasma corticotrophin-releasing hormone and its relation to gestational length

OBJECTIVE

To assess the relationship between rate of increase in maternal plasma corticotrophin-releasing hormone and gestational length.

DESIGN

A prospective observational study.

SETTING

Department of Obstetrics and Gynaecology, Prince of Wales Hospital, Hong Kong.

METHODS

Serial venous samples taken at four to six week intervals from 81 pregnant Chinese subjects were assayed for corticotrophin-releasing hormone concentrations. The investigators responsible for the laboratory assay were blinded to the obstetric outcome.

RESULTS

A total of 380 blood samples were taken. Each subject provided three to seven samples (median = 5). Seven of the 81 subjects had preterm delivery. Maternal corticotrophin-releasing hormone levels increased exponentially as gestation advanced. A negative correlation between the rate of rise of logarithmic equivalence of corticotrophin-releasing hormone concentrations (Ln-corticotrophin releasing hormone) per week and the gestational age at delivery was demonstrated (r = -0.45, P < 0.001). The rate of increase of Ln-corticotrophin releasing hormone concentrations per week was also significantly greater for those who delivered preterm before 37 weeks compared with those with uncomplicated term deliveries (0.27 Vs 0.22, P = 0.018).

CONCLUSIONS

The rate of increase in maternal plasma corticotrophin-releasing hormone is inversely proportional to gestational length. Results in a Chinese population confirm and extend results from previous caucasian populations. This study provides another piece of evidence on the close link between maternal plasma corticotrophin-releasing hormone and the timing of human parturition. As the hormone is synthesized by the placenta, it supports the suggestion that the human placenta has an important role in determining gestational length.

Circulating maternal corticotropin-releasing hormone and gonadotropin-releasing hormone in normal and abnormal pregnancies

OBJECTIVE

Corticotropin-releasing hormone and gonadotropin-releasing hormone are produced by the human placenta and have been measured in the maternal circulation during pregnancy. Our objective was to determine concentrations of these substances in maternal plasma throughout normal pregnancies and in early pregnancy loss.

STUDY DESIGN

Fifty-one pregnant women were followed up prospectively and plasma samples were drawn at 8, 10, 12, 14, 16, 28, and 36 weeks' gestation and during labor. Specific and sensitive radioimmunoassays were used to determine corticotropin-releasing hormone and gonadotropin-releasing hormone concentrations in these samples.

RESULTS

Blood samples were drawn at all time points and outcome data were available from 33 women who completed their pregnancies at term without complications. In this normal group circulating corticotropin-releasing hormone concentrations increased from low or undetectable concentrations at 8 weeks (< or = 23.2 +/- 1.3 pg/ml, mean +/- SEM) to measurable values at 16 weeks (34.3 +/- 2.2 pg/ml). Thereafter there was a significant increase to 1294 +/- 113 pg/ml in labor. Gonadotropin-releasing hormone demonstrated a trimodal distribution, increasing significantly from 8 to 14 weeks, decreasing at 16 weeks, and increasing again by term. The ratio of corticotropin-releasing hormone to gonadotropin-releasing hormone in the normal group demonstrated a 30-fold increase from 8 weeks to term. In eight cases of early pregnancy loss corticotropin-releasing hormone and gonadotropin-releasing hormone concentrations were not significantly different from those of the normal group in early pregnancy. In two cases of premature delivery gonadotropin-releasing hormone concentrations and ratios were within the normal range; corticotropin-releasing hormone levels were normal in both cases of premature delivery.

CONCLUSION

In this study we determined maternal concentrations of corticotropin-releasing hormone and gonadotropin-releasing hormone in normal pregnancies and in labor at term. Neither maternal concentrations of corticotropin-releasing hormone nor gonadotropin-releasing hormone were useful in identifying pregnant women at risk for early pregnancy loss.

New perspectives for the effective treatment of preterm labor

Preterm birth (before 37 completed weeks of gestation) continues to account for the vast majority of neonatal morbidity and mortality. The incidence of preterm birth can be reduced by appropriate social interventions and antenatal care. Currently available tocolytic agents suffer from low uterospecificity and prolong pregnancy only marginally, although postponement of birth by a few days may be of some value. Further progress is needed in at least four areas: prevention of preterm labor; identification of preterm labor; selection of candidates for tocolysis, and treatment of preterm labor. Effective, early treatment of vaginosis offers particular promise for the prevention of preterm labor and identification of specific biochemical markers will facilitate early detection of this process. Oxytocin antagonists offer greater specificity than current tocolytics and can be expected to show improved efficacy and risk profiles. Such compounds will allow more effective treatment of preterm labor with a lower risk of side effects.