Effect of maternal administration of thyrotropin releasing hormone on the preterm fetal pituitary-thyroid axis

Effects of betamethasone and thyroid releasing hormone on fetal lung maturation: an experimental and morphometric study

OBJECTIVE

To determine the effects of betamethasone and thyroid releasing hormone (TRH) on morphologic fetal rabbit lung maturation when administered separately and in combination.

MATERIAL AND METHODS

Twenty-five pregnant rabbits were divided into five groups. Study groups were as follows: TRH or betamethasone alone (between 24 and 27th days of gestation), TRH + betamethasone or betamethasone + TRH (second dose of drugs were added in the last 2 days), and the control. The pregnancies were terminated on the 27th day of gestation. Weights and volumes of the fetal lungs were determined and the results were compared.

RESULTS

Mean lung weights in all treatment groups were significantly heavier than controls (P < 0.05). The differences between mean lung weights of TRH alone, TRH + betamethasone, and betamethasone alone groups were not statistically significant (P > 0.05), but the mean lung weight of betamethasone + TRH group was significantly lower than the other treatment groups (P < 0.05). Mean lung volume of TRH alone group was significantly higher than control group; however, there were no significant differences between other treatment groups and the control. No correlation was found between the lung weights and volumes in all groups (r = 0.1, P > 0.05).

CONCLUSION

Only TRH alone treatment produced a significant increase in both fetal lung volume and weight compared to the control group. Administering TRH alone can lead to increased lung maturation. Combining TRH to corticosteroid treatment significantly decreased mean fetal lung weight, instead of an increase. According to these results combined used of these two substances probably counteract each others effect, instead of having a synergism.

Neurodevelopmental outcome of children treated with antenatal thyrotropin-releasing hormone

OBJECTIVE

To evaluate neurodevelopmental outcome until 2 years of age in children who participated in a multicenter antenatal thyrotropin-releasing hormone (TRH) trial to improve respiratory outcome and to lower mortality.

METHODS

Neurodevelopmental outcome was studied in infants whose mothers were admitted to the Academic Medical Center and enrolled in the European Antenatal TRH trial. Mothers were treated for imminent preterm delivery (before 30 weeks) with corticosteroids plus either placebo (placebo-group) or TRH (TRH-group). TRH treatment consisted of 400 micro g every 8 hours up to 4 doses. Assessments included neurologic development at 12 months and psychomotor development at 12 and 24 months using the Bayley developmental scales.

RESULTS

Sixty-two infants were included, 10 of whom died. Of the surviving infants, 24 received TRH and 28 received placebo. Ten infants were lost to follow-up. Each group consisted of 21 infants. Both groups were comparable regarding gestational age, birth weight, and time interval between trial medication and birth. However, in the TRH group, more respiratory problems, ventilator days, and chronic lung disease were found. Neurologic and motor outcome did not differ between the groups, but lower mental developmental index scores were found in the TRH group at both ages.

CONCLUSIONS

Antenatal TRH treatment is associated with a delay in mental development. This study demonstrates the importance of long-term follow-up of perinatal intervention trials with possible consequences for neurodevelopmental outcome of the infant.

Is there a role for antenatal TRH therapy for the prevention of neonatal lung disease?

Unfortunately, surfactant therapy is not routinely available to infants in some parts of the world because of its cost. It is the hypothesis of this article that in situations where surfactant is not available, there may be a role for antenatal thyrotropin-releasing hormone (TRH) plus glucocorticoid therapy. Data from randomized clinical trials, which compared therapy with antenatal glucocorticoid plus TRH to that with glucocorticoid alone were extracted and subjected to meta-analysis. The trials that incorporated surfactant therapy were analyzed separately from those in which surfactant was not used. In addition, because surfactant therapy was only available to some patients in the Australian ACTOBAT trial, each group analysis was performed with and without the ACTOBAT data. A characteristic of the earlier presurfactant trials is that few were designed for "intention to treat" analysis. In most of these studies, it was decided a priori to include babies who delivered within a specified time period after hormone therapy. The addition of TRH did not decrease respiratory distress syndrome in those trials in which surfactant therapy was used. In the presurfactant trials, respiratory distress syndrome was significantly decreased when "intention to treat" data were examined, as well as in those infants who delivered between 1 and 10 days after maternal therapy. There was also a significant decrease in oxygen dependency at 28 days after birth, and in oxygen dependency or death at this time, in those infants who delivered 1 to 10 days after treatment. Antenatal TRH had no significant effect of on neonatal complications such as air leak, intraventricular hemmorhage, patent ductus arteriosus, retinopathy of prematurity, or necrotizing enterocolitis. However, TRH did produce transient suppression of the pituitary thyroid axis. There were also a variety of transient complications in the mothers, including nausea, vomiting or flushing, light-headed feeling, and increased blood pressure. The authors conclude that the implementation of appropriate antenatal glucocorticoid treatment is the first priority. Once this has been established, the data presented here suggest that addition of antenatal TRH should be considered in those situations where surfactant is not available.

Two trials of antenatal thyrotrophin-releasing hormone for fetal maturation: stopping before the due date. Antenatal TRH Trial and the Thyroneth Trial Groups

OBJECTIVES

To determine whether the addition of antenatal thyrotrophin-releasing hormone (TRH) to corticosteroids, given to women at risk of preterm delivery, would decrease the risk of death and severe morbidity associated with prematurity.

DESIGN

Two concurrent multicentre, double blind, randomised, placebo-controlled trials were designed with a common core dataset to be analysed as a single large pragmatic trial.

SETTING

Hospital maternity units.

POPULATIONS

Pregnant women at risk of preterm delivery who had been prescribed a course of corticosteroids to enhance fetal maturation.

INTERVENTIONS

Antenatal administration of TRH 400 microg every eight hours for four doses versus matching placebo.

MAIN OUTCOME MEASURES

Primary: death of the baby or chronic lung disease (defined as oxygen dependency at 28 days after birth). Secondary: other measures of respiratory morbidity, in particular respiratory distress syndrome. Other measures of short term neonatal morbidity including intraventricular haemorrhage and necrotising enterocolitis. Measures of maternal side effects.

RESULTS

The antenatal TRH trial was halted early on the basis of external evidence. Overall a total of 225 women were recruited who delivered 275 babies. The primary outcome of death or chronic lung disease occurred in 33 babies in the TRH group and 43 babies in the placebo group (RR 0.8, 95% CI 0.5-1.2). There were no other differences between the two groups. Stratified analysis did not reveal any differences between the two groups depending on how long before the time of delivery the mother had received the TRH or placebo.

CONCLUSIONS

These trials are too small to provide convincing evidence of the effect of antenatal TRH on neonatal outcome. When added to the existing systematic review and meta-analysis, however, these data should provide evidence on which subsequent practice can be based. The process by which the trials were monitored and stopped is of relevance to future trials.

Plasma thyroid hormones in premature infants: effect of gestational age and antenatal thyrotropin-releasing hormone treatment. TRH Collaborative Trial Participants

Thyroid hormones are important for both perinatal adaptation and long-term psychomotor development; however, there is limited information on the effects of extreme prematurity and antenatal TSH-releasing hormone (TRH) treatment on pituitary-thyroid function. In this study we assayed plasma triiodothyronine (T3) and TSH in infants who were part of a collaborative trial of antenatal maternal TRH therapy. Within the control population (n = 166), infants of 24-28-wk and 28-32-wk gestational age had comparable levels of T3 (0.94 and 1.06 nmol/L, respectively) and TSH (5.7 and 7.2 mU/L) at birth, but the increases at 2 h and subsequent T3 levels were less in the 24-28 wk versus 28-32-wk gestation infants. In the TRH-treated group (n = 131), T3 was lower in the first day for infants delivered 7-72 h after antenatal TRH compared with control infants. TSH at birth was approximately 3.5-fold greater for infants delivered at 0-6 h after the last TRH dose compared with the control group and was suppressed in infants delivering at 7-36 h. T3 and TSH levels were not different between control and TRH-treated groups at 3-28 d of age. In TRH stimulation tests on d 28, control and TRH-treated groups had similar peak levels of TSH and incidence of exaggerated response (TSH > or = 35 mU/L). We conclude that extremely premature infants have a reduced postnatal surge in TSH and T3 and maintain lower T3 concentrations, probably reflecting tertiary hypothyroidism. The stimulatory and suppressive effects of antenatal TRH treatment observed at birth are transient and do not affect pituitary-thyroid responsiveness at 28 d of age.

Antenatal thyrotropin-releasing hormone to prevent lung disease in preterm infants. North American Thyrotropin-Releasing Hormone Study Group

BACKGROUND

Pulmonary disease is common in preterm infants, despite antenatal glucocorticoid therapy. The addition of antenatal thyrotropin-releasing hormone therapy has been reported to decrease pulmonary morbidity in these infants.

METHODS

We enrolled 996 women at 13 North American centers who were in preterm labor at <30 weeks' gestation in a double-blind, placebo-controlled, randomized trial of antenatal thyrotropin-releasing hormone, given intravenously in four doses of 400 microg each at eight-hour intervals. The primary outcome was chronic lung disease or death of the infant on or before the 28th day after delivery, and secondary outcomes were respiratory distress syndrome and chronic lung disease or death at 36 weeks' postmenstrual age. Complete data were available for 981 women and their 1134 live-born infants. The 769 infants born at < or = 32 weeks' gestation were defined as the group at risk.

RESULTS

There were no significant differences between the at-risk treatment and placebo groups in mean (+/-SD) birth weight (1109+/-354 vs. 1097+/-355 g), gestational age (27.9+/-2.1 vs. 27.9+/-2.1 weeks), sex, or race. The frequencies of respiratory distress syndrome (66 percent vs. 65 percent), death at 28 days (11 percent vs. 11 percent), chronic lung disease or death at 28 days (45 percent vs. 42 percent) and at 36 weeks (32 percent vs. 34 percent), and other neonatal complications as well as the severity of lung disease were not significantly different in the at-risk treatment and placebo groups. Similarly, there were no differences in outcome between the treatment and placebo groups for the infants born at >32 weeks' gestation.

CONCLUSIONS

In preterm infants at risk for lung disease, antenatal administration of thyrotropin-releasing hormone and glucocorticoid is no more beneficial than glucocorticoid alone.

Collaborative trial of prenatal thyrotropin-releasing hormone and corticosteroids for prevention of respiratory distress syndrome. Collaborative Santiago Surfactant Group

OBJECTIVE

Our purpose was to determine whether adding antenatal thyrotropin-releasing hormone to prenatal corticosteroids reduces the frequency of respiratory distress syndrome.

STUDY DESIGN

A randomized, multicenter, double-blind, placebo-controlled trial was conducted of thyrotropin-releasing hormone (400 micrograms intravenously every 8 hours four times) in women with singleton pregnancies < 33 weeks of gestation who received antenatal betamethasone (12 mg intramuscularly every 24 hours two times). Neonates weighing < 1.0 kg received prophylactic surfactant and those above that weight received rescue therapy.

RESULTS

One hundred ninety women received thyrotropin-releasing hormone and 180 were given placebo. There were no differences in the frequency of respiratory distress syndrome (relative risk 1.17 [95% confidence interval 0.93 to 1.48]), use of oxygen at age 28 days (1.14 [0.80 to 1.62]), or neonatal mortality (1.05 [0.79 to 1.38]). Air leaks were more frequent in the thyrotropin-releasing hormone group (1.57 [1.23 to 2.01]).

CONCLUSIONS

The combination of antenatal thyrotropin-releasing hormone and corticosteroids does not reduce the frequency of respiratory distress syndrome or improve the outcome of preterm neonates compared with the use of corticosteroids alone.

Maternofetal transfer of thyrotrophin-releasing hormone: effect of concentration and mode of administration

We studied the effect of maternal concentration and mode of administration on transfer rate of TSH-releasing hormone (TRH) in an in vitro model of dually perfused isolated lobule of human term placenta. Varying concentrations (4-40 microg dL(-1)) of TRH were added either to the open maternal circulation to mimic an infusion or as a single bolus dose to the closed maternal circulation. TRH was measured by RIA. Perfusion efficiency in each experiment was determined by using antipyrine and creatinine as diffusable markers. At a concentration equivalent to the usual clinical dose of 400 microg, transplacental transfer of TRH was 0.4 +/- 0.1%, with an fetal/maternal ratio of 0.01 +/- 0.003. Placental clearance rate (y = 0.07x; R2 = 0.97; p < 0.001; n = 28) and uptake of TRH (y = 0.40x; R2 = 0.95; p < 0.001) in the closed experiments increased exponentially with increasing maternal concentration. Placental clearance (y = 0.05x; R2 = 0.99; p < 0.001; n = 30), and uptake of TRH (y = 0.35x; R2 = 0.98; p < 0.01) under steady state also correlated with maternal TRH concentration. For a given concentration, placental clearance and uptake of TRH was comparable whether given as a bolus or an infusion. We conclude that TRH is transferred sparingly across the human term placenta and its transfer rate is a function of the maternal concentration of TRH and not its mode of administration.

[Prenatal corticotherapy and acceleration of fetal maturation. II. Results of clinical applications]

Numerous subsequent controlled trials and recent meta-analysis have confirmed the efficiency of antenatal glucocorticoid therapy in reducing both the incidence of respiratory distress syndrome (RDS) and perinatal mortality. Moreover, antenatal glucocorticoid administration reduces the odds of several severe complications relating to immaturity: intraventricular hemorrhage (IVH), ductus arteriosus patency, necrotising enterocolitis, and hemodynamic failure. Exogenous surfactant therapy has not ruled out the benefits of corticosteroids: on the contrary, a synergic effect is obtained when both antenatal and postnatal therapeutic approaches are combined. Very premature infants may also take advantage of the hormonal treatment: in this population, RDS occurrence, IVH incidence and perinatal mortality are also reduced. Unfortunately, despite convincing evidence, the incidence of antenatal steroids therapy has not yet achieved the optimal and desirable level. Obstetricians and pediatricians must be encouraged to ensure high maternal exposure to steroids when preterm delivery is likely to occur.

Thyrotropin-releasing hormone: does two hundred micrograms provide effective stimulation to the preterm fetal pituitary gland compared with four hundred micrograms?

OBJECTIVE

Our purpose was to compare the response of the fetal pituitary-thyroid axis to 200 and 400 micrograms of thyrotropin-releasing hormone administered to the mother immediately before delivery with a control group.

STUDY DESIGN

A randomized controlled trial was conducted of 26 women at gestational ages between 24 weeks and 33 weeks 6 days who had received one or more doses of betamethasone who were expected to be delivered within 1 to 4 hours. Women received either 200 or 400 micrograms of thyrotropin-releasing hormone or were in the control group.

RESULTS

Thyroid-stimulating hormone determinations on cord blood had a higher mean level in both treatment groups compared with the control group. No differences were seen in cord blood results between the two treatment groups for thyroid-stimulating hormone, thyroxine, triiodothyronine, free thyroxine, free triiodothyronine, and prolactin levels. The only other differences found were in a higher level in total thyroxine and a lower level of free thyroxine in the 400 micrograms thyrotropin-releasing hormone group compared with the 200 micrograms group in the 48-hour blood determinations.

CONCLUSION

Both 200 and 400 micrograms of thyrotropin-releasing hormone provided fetal pituitary stimulation, as reflected in fetal thyroid-stimulating hormone levels in cord blood, and both gave significantly higher levels compared with a control group.

Maternal administration of glucocorticoid and thyrotropin-releasing hormone enhances fetal lung maturation in undisturbed preterm lambs

OBJECTIVE

We hypothesized that combined treatment with glucocorticoid plus thyrotropin-releasing hormone administered to pregnant ewes with preterm gestation accelerates fetal lung maturation of undisturbed lambs better than single hormonal treatment does.

STUDY DESIGN

Twenty-five pregnant ewes at 123 days of gestation were randomized to receive (1) 0.9% sodium chloride (controls), (2) betamethasone (12 mg intramuscularly every 24 hours two times), (3) thyrotropin-releasing hormone (400 micrograms intravenously every 8 hours six times), or (4) thyrotropin-releasing hormone plus betamethasone. After delivery by cesarean section at 125 days fetal lamb lung compliance and alveolar lavage phospholipid content were determined.

RESULTS

Betamethasone plus thyrotropin-releasing hormone significantly increased fetal lung compliance expressed as milliliters of air per gram of wet weight at 40 cm H2O and 5 cm H2O (0.82 +/- 0.13 and 0.35 +/- 0.10 ml/gm wet lung, respectively) versus betamethasone (0.37 +/- 0.02 and 0.07 +/- 0.02), thyrotropin-releasing hormone (0.38 +/- 0.02 and 0.14 +/- 0.03), and control (0.25 +/- 0.03 and 0.09 +/- 0.01) groups. Also, total phospholipids and saturated phosphatidylcholine concentrations in alveolar lavage were significantly higher in the combined betamethasone plus thyrotropin-releasing hormone group (27.3 +/- 4.9 and 16.9 +/- 4.3 micrograms/gm wet lung, respectively) versus betamethasone (10.9 +/- 3.5 and 6.7 +/- 2.1), thyrotropin-releasing hormone (15.2 +/- 5.6 and 7.3 +/- 2.0), and control (7.9 +/- 2.4 and 3.6 +/- 1.0) groups.

CONCLUSION

Combined maternal administration of betamethasone plus thyrotropin-releasing hormone improves lung maturation in undisturbed fetal lambs at 125 days' gestation more than does either hormone given alone.

A randomized, controlled trial of antepartum thyrotropin-releasing hormone and betamethasone in the prevention of respiratory disease in preterm infants

OBJECTIVE

The objective was to investigate whether the addition of thyrotropin-releasing hormone to antepartum betamethasone further reduces the incidence of respiratory disease in preterm infants.

STUDY DESIGN

A randomized, placebo-controlled, double-blind trial of antepartum thyrotropin-releasing hormone (400 micrograms given intravenously four times) and betamethasone (5 mg given intramuscularly four times) was conducted in 378 mothers likely to be delivered between 24 and 32.6 weeks' gestation. Statistical analysis was by relative risk, chi 2, t tests, and multiple logistic regression analysis.

RESULTS

Four hundred five live-born infants were delivered. In infants without lethal abnormalities delivered between 24 hours and 10 days from entry (n = 175) the incidence of respiratory distress syndrome was reduced from 52% to 31% (relative risk 0.61, 95% confidence interval 0.41 to 0.89) and that of severe respiratory distress syndrome from 42% to 20% (relative risk 0.48, 95% confidence interval 0.29 to 0.78) in the placebo and thyrotropin-releasing hormone groups, respectively. The number of deaths fell from 14 to one (relative risk 0.08, 95% confidence interval 0.01 to 0.63). The incidence of chronic lung disease was not significantly different, but that of an adverse outcome (chronic lung disease or death by 36 weeks' gestation) fell from 29% in the placebo group to 16% with thyrotropin-releasing hormone (relative risk 0.55, 95% confidence interval 0.31 to 0.99).

CONCLUSION

The addition of thyrotropin-releasing hormone to antepartum glucocorticoid treatment reduces the incidence of respiratory distress syndrome and improves survival in preterm infants.