Fetal growth retardation, particularly within lymphoid organs, following repeated maternal injections of betamethasone in sheep

Effect of maternal betamethasone administration on feto-placental vascular resistance in the mouse†

Antenatal corticosteroids are often administered to women at risk of preterm birth to accelerate fetal lung development; however, there is evidence that this treatment may adversely affect placental function in some fetuses. Our group has recently demonstrated that wave reflections in the umbilical artery (UA), measured using high-frequency ultrasound, are sensitive to placental vascular abnormalities. In the present study, we used this approach to investigate the effect of maternal administration of betamethasone, a clinically relevant corticosteroid, on the feto-placental vasculature of the mouse. Fetuses were assessed at embryonic day (E)15.5 and E17.5 in C57BL6/J mice. At both gestational ages, the UA diameter, UA blood flow, and the wave reflection coefficient were significantly elevated in the betamethasone-treated mice compared to vehicle-treated controls. These observations support the interpretation that placental vascular resistance dropped with betamethasone treatment to an extent that could not be explained by vasodilation of the UA alone. Consistent with clinical studies, the effect of betamethasone on UA end-diastolic velocity was heterogeneous. Our results suggest that UA wave reflections are more sensitive to acute changes in placental vascular resistance compared with the UA pulsatility index, and this technique may have clinical application to identify a favorable placental vascular response to fetal therapies such as antenatal corticosteroids, where the fetal heart rate is likely to vary.

The critical importance of the fetal hypothalamus-pituitary-adrenal axis

The fetal hypothalamus-pituitary-adrenal (HPA) axis is at the center of mechanisms controlling fetal readiness for birth, survival after birth and, in several species, determination of the timing of birth. Stereotypical increases in fetal HPA axis activity at the end of gestation are critical for preparing the fetus for successful transition to postnatal life. The fundamental importance in fetal development of the endogenous activation of this endocrine axis at the end of gestation has led to the use of glucocorticoids for reducing neonatal morbidity in premature infants. However, the choice of dose and repetition of treatments has been controversial, raising the possibility that excess glucocorticoid might program an increased incidence of adult disease (e.g., coronary artery disease and diabetes). We make the argument that because of the critical importance of the fetal HPA axis and its interaction with the maternal HPA axis, dysregulation of cortisol plasma concentrations or inappropriate manipulation pharmacologically can have negative consequences at the beginning of extrauterine life and for decades thereafter.

Ovine fetal thymus response to lipopolysaccharide-induced chorioamnionitis and antenatal corticosteroids

Rationale

Chorioamnionitis is associated with preterm delivery and involution of the fetal thymus. Women at risk of preterm delivery receive antenatal corticosteroids which accelerate fetal lung maturation and improve neonatal outcome. However, the effects of antenatal corticosteroids on the fetal thymus in the settings of chorioamnionitis are largely unknown. We hypothesized that intra-amniotic exposure to lipopolysaccharide (LPS) causes involution of the fetal thymus resulting in persistent effects on thymic structure and cell populations. We also hypothesized that antenatal corticosteroids may modulate the effects of LPS on thymic development.

Methods

Time-mated ewes with singleton fetuses received an intra-amniotic injection of LPS 7 or 14 days before preterm delivery at 120 days gestational age (term = 150 days). LPS and corticosteroid treatment groups received intra-amniotic LPS either preceding or following maternal intra-muscular betamethasone. Gestation matched controls received intra-amniotic and maternal intra-muscular saline. The fetal intra-thoracic thymus was evaluated.

Results

Intra-amniotic LPS decreased the cortico-medullary (C/M) ratio of the thymus and increased Toll-like receptor (TLR) 4 mRNA and CD3 expression indicating involution and activation of the fetal thymus. Increased TLR4 and CD3 expression persisted for 14 days but Foxp3 expression decreased suggesting a change in regulatory T-cells. Sonic hedgehog and bone morphogenetic protein 4 mRNA, which are negative regulators of T-cell development, decreased in response to intra-amniotic LPS. Betamethasone treatment before LPS exposure attenuated some of the LPS-induced thymic responses but increased cleaved caspase-3 expression and decreased the C/M ratio. Betamethasone treatment after LPS exposure did not prevent the LPS-induced thymic changes.

Conclusion

Intra-amniotic exposure to LPS activated the fetal thymus which was accompanied by structural changes. Treatment with antenatal corticosteroids before LPS partially attenuated the LPS-induced effects but increased apoptosis in the fetal thymus. Corticosteroid administration after the inflammatory stimulus did not inhibit the LPS effects on the fetal thymus.

Multiple courses of antenatal corticosteroids for preterm birth (MACS): a randomised controlled trial

BACKGROUND

One course of antenatal corticosteroids reduces the risk of respiratory distress syndrome and neonatal death. Weekly doses given to women who remain undelivered after a single course may have benefits (less respiratory morbidity) or cause harm (reduced growth in utero). We aimed to find out whether multiple courses of antenatal corticosteroids would reduce neonatal morbidity and mortality without adversely affecting fetal growth.

METHODS

1858 women at 25-32 weeks' gestation who remained undelivered 14-21 days after an initial course of antenatal corticosteroids and continued to be at high risk of preterm birth were randomly assigned to multiple courses of antenatal corticosteroids (n=937) or placebo (n=921), every 14 days until week 33 or delivery, whichever came first. The primary outcome was a composite of perinatal or neonatal mortality, severe respiratory distress syndrome, intraventricular haemorrhage (grade III or IV), periventricular leucomalacia, bronchopulmonary dysplasia, or necrotising enterocolitis. Analysis was by intention to treat. All patients and caregivers were unaware of the treatment given. This trial is registered as number ISRCTN2654148.

FINDINGS

Infants exposed to multiple courses of antenatal corticosteroids had similar morbidity and mortality to those exposed to placebo (150 [12.9%] vs 143 [12.5%]). Those receiving multiple doses of corticosteroids also weighed less at birth than those exposed to placebo (2216 g vs 2330 g, p=0.0026), were shorter (44.5 cm vs 45.4 cm, p<0.001), and had a smaller head circumference (31.1 cm vs 31.7 cm, p<0.001).

INTERPRETATION

Multiple courses of antenatal corticosteroids, every 14 days, do not improve preterm-birth outcomes, and are associated with a decreased weight, length, and head circumference at birth. Therefore, this treatment schedule is not recommended.

FUNDING

Canadian Institutes of Health Research.

Single Versus Repeat Courses of Antenatal Steroids to Improve Neonatal Outcomes: Risks and Benefits

Recent additions to the literature provide evidence supporting the use of repeat courses of antenatal steroids. Both human and animal studies offer evidence that repeat courses of corticosteroids improve neonatal pulmonary outcomes, especially for the infants delivered at earlier gestational ages. Although there is also evidence to suggest altered neuronal maturation and intrauterine growth restriction in animals treated with repeat steroids, randomized controlled studies in humans have shown that birth weight reduction was only seen in those infants treated with 4 or more courses of corticosteroids. In addition, the reduction in neonatal birth weight and head circumference seen after multiple courses of antenatal corticosteroids normalizes by the time of hospital discharge. Studies are ongoing to investigate the 24-month post delivery physical and neurodevelopmental outcomes in infants exposed to repeat courses of antenatal corticosteroids. Although there is evidence demonstrating the safety of a single repeat, or 'rescue', dose of antenatal corticosteroids, this must be tempered against the adverse effects seen after multiple courses of weekly repeat steroids. Randomized controlled trials are needed to determine the optimal number of courses of antenatal steroids to reduce the frequency of neonatal respiratory distress syndrome (RDS) without adversely affecting other neonatal outcomes.

The endocrinology of pregnancy and fetal loss in wild baboons

An impressive body of research has focused on the mechanisms by which the steroid estrogens (E), progestins (P), and glucocorticoids (GC) ensure successful pregnancy. With the advance of non-invasive techniques to measure steroids in urine and feces, steroid hormones are routinely monitored to detect pregnancy in wild mammalian species, but hormone data on fetal loss have been sparse. Here, we examine fecal steroid hormones from five groups of wild yellow baboons (Papio cynocephalus) in the Amboseli basin of Kenya to compare the hormones of successful pregnancies to those ending in fetal loss or stillbirth. Using a combination of longitudinal and cross-sectional data, we analyzed three steroid hormones (E, P, GC) and related metabolites from 5 years of fecal samples across 188 pregnancies. Our results document the course of steroid hormone concentrations across successful baboon pregnancy in the wild and demonstrate that fecal estrogens predicted impending fetal loss starting 2 months before the externally observed loss. By also considering an additional 450 pregnancies for which we did not have hormonal data, we determined that the probability for fetal loss for Amboseli baboons was 13.9%, and that fetal mortality occurred throughout gestation (91 losses occurred in 656 pregnancies; rates were the same for pregnancies with and without hormonal data). These results demonstrate that our longstanding method for early detection of pregnancies based on observation of external indicators closely matches hormonal identification of pregnancy in wild baboons.

Stress Hormones: A Link between Maternal Condition and Sex‐Biased Reproductive Investment

In species where offspring fitness is sex-specifically influenced by maternal reproductive condition, sex allocation theory predicts that poor-quality mothers should invest in the evolutionarily less expensive sex. Despite an accumulation of evidence that mothers can sex-specifically modulate investment in offspring in relation to maternal quality, few mechanisms have been proposed as to how this is achieved. We explored a hormonal mechanism for sex-biased maternal investment by measuring and experimentally manipulating baseline levels of the stress hormone corticosterone in laying wild female European starlings (Sturnus vulgaris) and examining effects on sex ratio and sex-specific offspring phenotype adjustment. Here we show that baseline plasma corticosterone is negatively correlated with energetic body condition in laying starlings, and subsequent experimental elevation of maternal baseline plasma corticosterone increased yolk corticosterone without altering maternal condition or egg quality per se. Hormonal elevation resulted in the following: female-biased hatching sex ratios (caused by elevated male embryonic mortality), lighter male offspring at hatching (which subsequently grew more slowly during postnatal development), and lower cell-mediated immune (phytohemagglutinin) responses in males compared with control-born males; female offspring were unaffected by the manipulation in both years of the study. Elevated maternal corticosterone therefore resulted in a sex-biased adjustment of offspring quality favorable to female offspring via both a sex ratio bias and a modulation of male phenotype at hatching. In birds, deposition of yolk corticosterone may benefit mothers by acting as a bet-hedging strategy in stochastic environments where the correlation between environmental cues at laying (and therefore potentially maternal condition) and conditions during chick-rearing might be low and unpredictable. Together with recent studies in other vertebrate taxa, these results suggest that maternal stress hormones provide a mechanistic link between maternal quality and sex-biased maternal investment in offspring.

Sexually dimorphic effects of maternal asthma during pregnancy on placental glucocorticoid metabolism and fetal growth

Human pregnancy is associated with sexually dimorphic differences in mortality and morbidity of the fetus with the male fetus experiencing the poorest outcome following complications such as pre-eclampsia, pre-term delivery and infection. The physiological mechanisms that confer these differences have not been well characterised in the human. Work conducted on the effect of maternal asthma during pregnancy, combining data collected from the mother, placenta and fetus has found some significant sex-related mechanistic differences associated with fetal growth in both normal pregnancies and pregnancies complicated by asthma. Specifically, sexually dimorphic differences have been found in placental glucocorticoid metabolism in male and female fetuses of normal pregnancies. In response to the presence of maternal asthma, only the female fetus alters placental glucocorticoid metabolism resulting in decreased growth. The male fetus does not alter placental function or growth in response to maternal asthma. As a result of the alterations in glucocorticoid metabolism in the female, downstream changes occur in pathways regulated by glucocorticoids. These data suggest that the female fetus adjusts placental function and reduces growth to compensate for maternal disease. However, the male fetus continues to grow in response to maternal asthma with no changes in placental function. This response by the male fetus may partially contribute to the increased risk of morbidity and mortality in this sex.

ACTH-induced stress response during pregnancy in a viviparous gecko: no observed effect on offspring quality

The typical stress response in reptiles involves the release of corticosterone from the adrenal glands. Elevated maternal concentrations of corticosterone in mammals during pregnancy may have deleterious effects on offspring fitness, and recent work has shown a suppression of the hormonal response to stress during pregnancy in rats. Little is known about the influence of reproductive state on the secretion of corticosterone in viviparous reptiles or on the effects of high levels of corticosterone during reproduction on the developing embryos. We examined whether New Zealand common geckos (Hoplodactylus maculatus), pregnant with embryos at stages 34-35 of development, secrete corticosterone in response to adrenocorticotrophic hormone (ACTH) and whether an ACTH-induced increase in maternal corticosterone affects the outcome of pregnancy. Corticosterone concentrations in pregnant lizards increased more than seven-fold over basal levels following injection of ACTH. However, there were no significant effects of elevated corticosterone on the duration or success of pregnancy, or on various morphological measures, growth, or sprint speed of the offspring. This may reflect a lack of sensitivity of relevant embryonic tissues to corticosterone under the conditions of the present experiment or an ability of the embryos to bind, degrade, or restrict placental transport of corticosterone. Future studies should investigate the possibility of corticosteroid effects on other offspring tissues, including effects in adult life.

Perinatal corticosteroids: A review of research. Part I: Antenatal administration

The premature infant may receive therapeutic glucocorticoid drugs while in utero or in the postnatal period. This article (part I of a two-part series) discusses the benefits and risks of in utero, or antenatal, corticosteroids (ACS) for the premature infant. Part II addresses the benefits and risks of postnatal corticosteroid (PCS) use. There are numerous clinical studies on the therapeutic use of these steroids for the prevention of respiratory distress syndrome and chronic lung disease in the premature infant, although research results on the efficacy of repeated steroid exposure among premature infants vary. Premature infants who are exposed to repeated courses of ACS and/or high-cumulative-dose PCS may show no neurologic side effects until later in life. Research in newborn animal models focused on the timing, duration, and amounts of ACS and PCS. Current clinical research includes examination of the neurodevelopment of infants who are therapeutically exposed to perinatal corticosteroids, to identify safer minimal dose protocols. Over the past 30 years, corticosteroids have been increasingly prescribed before and after birth. Understanding the potential treatment benefits and risks to human fetuses and neonates is vital to clinical practice. This review presents historic and pharmacokinetic information about prenatal use of corticosteroids. It also offers scientific evidence of the benefits and risks identified in animal models and clinical trials, to stimulate thought that gtiides neonatal clinical practice.

Protecting embryos from stress: corticosterone effects and the corticosterone response to capture and confinement during pregnancy in a live-bearing lizard (Hoplodactylus maculatus)

Hormones in the embryonic environment, including those of the hypothalamo-pituitary-adrenal (HPA) axis, have profound effects on development in eutherian mammals. However, little is known about their effects in reptiles that have independently evolved viviparity. We investigated whether exogenous corticosterone affected embryonic development in the viviparous gecko Hoplodactylus maculatus, and whether pregnant geckos have a corticosterone response to capture and confinement that is suppressed relative to that in non-pregnant (vitellogenic) females and males. Corticosterone implants (5 mg, slow-release) administered to females in mid-pregnancy caused a large elevation of corticosterone in maternal plasma (P<0.001), probable reductions in embryonic growth and development (P=0.069-0.073), developmental abnormalities and eventual abortions. Cool temperature produced similar reductions in embryonic growth and development (P< or =0.036 cf. warm controls), but pregnancies were eventually successful. Despite the potentially harmful effects of elevated plasma corticosterone, pregnant females did not suppress their corticosterone response to capture and confinement relative to vitellogenic females, and both groups of females had higher responses than males. Future research should address whether lower maternal doses of corticosterone produce non-lethal effects on development that could contribute to phenotypic plasticity. Corticosterone implants also led to increased basking in pregnant females (P<0.001), and basal corticosterone in wild geckos (independent of reproductive condition) was positively correlated with body temperature (P<0.001). Interactions between temperature and corticosterone may have broad significance to other terrestrial ectotherms, and body temperature should be considered as a variable influencing plasma corticosterone concentrations in all future studies on reptiles.

Repeated prenatal corticosteroids reduce glial fibrillary acidic protein in the ovine central nervous system

INTRODUCTION

A single course of corticosteroid reduces intracranial hemorrhage in preterm infants. The mechanism of protection is unclear. Glial fibrillary acidic protein (GFAP), expressed by astrocytes, is regulated by glucosteroids and is an important component of the cells forming the blood brain barrier. We have evaluated the effect of prenatal corticosteroid upon ovine GFAP.

METHODS

Date-mated ewes were studied in two protocols and lambs delivered on day 125 or 145 (term = 150). In the maternal injection protocol (n = 36) ewes were administered saline, single or repeated injections of corticosteroid. In the fetal injection protocol (n = 48) direct ultrasound-guided fetal injections of saline, single or repeated corticosteroid were administered, and an additional control group did not receive fetal injections. Optic nerve GFAP immunohistochemistry was performed and quantified.

RESULTS

At 125 days, repeated, but not single, administration of corticosteroid, by either maternal or fetal route, was associated with a significant reduction in GFAP (both p < 0.002); by 145 days, the deficit had recovered (both p > 0.05). The process of performing repeated fetal injections had an independent effect upon GFAP at 145 days (p = 0.002).

CONCLUSION

Repeated administration of corticosteroid results in a reduction in GFAP in the developing ovine optic nerve, with recovery demonstrated by 145 days.

Antenatal dexamethasone: effect on ovine placental 11beta-hydroxysteroid dehydrogenase type 2 expression and fetal growth

Antenatal glucocorticoids are routinely given to women at risk for preterm delivery. The fetus is protected from excessive glucocorticoids by the placental enzyme 11beta-hydroxysteroid dehydrogenase type 2 (11beta-HSD-2), which catalyzes the conversion of cortisol to its biologically inactive metabolite, cortisone. We examined the effects of antenatal dexamethasone on the expression of placental 11beta-HSD-2 in fetal sheep. Ewes were randomized to receive repeated or single courses of dexamethasone or placebo beginning at 76-78 or 104-106 d of gestation, respectively. In the single course group, the ewes received dexamethasone (6 mg, n = 7) or placebo (n = 6) as four intramuscular injections over 48 h up to 18 h before placental harvest. In the repeated course group, the ewes received the same treatment (dexamethasone, n = 10, or placebo, n = 9) once a week for 5 consecutive weeks starting at 76-78 d of gestation. Placental harvest occurred at 106-108 d of gestation in the four groups. By semi-quantitative RT-PCR, we found that placental 11beta-HSD-2 expression was lower in the fetuses of ewes exposed to a single course of dexamethasone than placebo (p < 0.05). Placental 11beta-HSD-2 expression did not differ significantly between fetuses of ewes treated with repeated courses of dexamethasone compared with placebo, or a single course of dexamethasone. Fetuses of dexamethasone treated ewes weighed less than those of placebo treated ewes (ANOVA, main effects for dexamethasone versus placebo treatment: F = 14.5, p = 0.007). Fetuses of ewes exposed to repeated courses of dexamethasone weighed less than those of ewes exposed to placebo or a single course of dexamethasone (p < 0.05). We conclude that maternal antenatal dexamethasone treatment reduces placental 11beta-HSD-2 expression and fetal weight at mid-gestation in the ovine pregnancy.

Cohort study of the neonatal outcome of twin pregnancies that were treated with prophylactic or rescue antenatal corticosteroids

OBJECTIVE

The purpose of this study was to compare the neonatal outcome of 2 approaches to antenatal corticosteroid therapy for threatened preterm delivery in twins: a prophylactic approach in which corticosteroids were administered every 2 weeks from 24 to 32 weeks of gestation and a rescue approach in which corticosteroids were given to women at immediate risk of preterm delivery.

STUDY DESIGN

A retrospective cohort study of 1038 twin babies delivered between 1990 and 1996 in a University Teaching Hospital. One hundred thirty-six babies were exposed to prophylactic therapy, and 902 babies were treated expectantly with rescue therapy.

RESULTS

Prophylactic corticosteroids were not associated with a significant reduction in respiratory distress syndrome (adjusted odds ratio, 0.7; 95% CI, 0.2-2.0). Unnecessary therapy was more likely with a prophylactic policy (relative risk, 7.5; 95% CI, 5.3-10.7) and was associated with a reduction in mean birth weight in term babies of 129 g (95% CI, -218 to -33; P =.008).

CONCLUSION

Prophylactic corticosteroids have no proven beneficial effect on the risk of respiratory distress syndrome in preterm twin babies. Such a policy exposes a large number of babies to unnecessary treatment that adversely affects growth.

Treatment of preterm labor

The ultimate goal of treating preterm labor is to prolong the pregnancy long enough to decrease the incidence of neonatal mortality and morbidity associated with prematurity, while minimizing maternal and fetal risks. There are many controversies in treating preterm labor. Much of this controversy stems from the difficulty in establishing efficacy and safety of interventions and uncertainty of the diagnosis of preterm labor. This article outlines conventional measures and tocolytic therapy directed at prolonging the pregnancy. A review of the effect of tocolytic agents, administration, side effects, and nursing interventions is included. Key words: preterm labor treatment,

Repeated doses of antenatal corticosteroids in animals: a systematic review

OBJECTIVE

The purpose of this review was to assess the effects of repeated doses of antenatal corticosteroids on lung and brain function and on growth restriction in animals.

STUDY DESIGN

MEDLINE and EMBASE were searched for randomized controlled trials that compared repeated doses of antenatal corticosteroids versus a single dose, with or without placebo, in pregnant animals.

RESULTS

Nineteen studies were included. The animals that were studied included sheep, monkeys, rabbits, and mice. There were 8 studies that assessed the effects of repeated doses of antenatal corticosteroids on lung function. All the studies reported improvement in lung function after repeated doses of antenatal corticosteroids. Seven studies investigated the effects of repeated doses of antenatal corticosteroids on brain or nervous system function or growth; all the studies found adverse effects with repeated doses of antenatal corticosteroids. Eleven studies looked at the effect of repeated doses of antenatal corticosteroids on fetal growth. Nine studies found evidence of fetal growth restriction with repeated doses of antenatal corticosteroids. One study assessed long-term behavioral outcomes in mice and found no effect.

CONCLUSION

Evidence from randomized controlled trials in animals suggests that repeated doses of antenatal corticosteroids may have beneficial effects in terms of lung function but may have adverse effects on brain function and fetal growth. Because of the differences between animals and humans, it is difficult to extrapolate directly the results of these studies to humans. Therefore, randomized controlled trials in humans are needed to assess the effects of repeated courses of antenatal corticosteroids for pregnant women who are at increased risk of preterm birth in terms of important perinatal, neonatal, and maternal outcomes.

Antenatal corticosteroids for preterm birth

A single course of antenatal corticosteroids is a rare example of a treatment that yields both a health benefit and a cost savings. This article reviews the history and background of antenatal corticosteroids, its use in clinical practice and the controversy today regarding the use of multiple courses of antenatal corticosteroids.

Repeated ultrasound guided fetal injections of corticosteroid alter nervous system maturation in the ovine fetus

INTRODUCTION

Recent studies in sheep have shown that repeated maternal injections of betamethasone are associated with adverse effects within the nervous system. Repeated fetal injections of betamethasone achieve serial improvements in preterm lung function in sheep and are a possible alternative to repeated maternal therapy. We have evaluated the effect of repeated fetal administration of betamethasone on nervous system maturation in an ovine model.

METHODS

Date-mated ewes (n = 48) were randomized to receive ultrasound-guided fetal injections of betamethasone or saline between days 104 to 124 of gestation and were delivered by cesarean section on day 125 or 145 (term = 150). Optic and sciatic nerves were prepared for light and electronmicroscopy. Eye diameters were measured and transverse sections of retinae were evaluated. Data were analyzed using a mixed model analysis of variance.

RESULTS

Repeated fetal administration of corticosteroid did not significantly affect optic nerve myelination but resulted in significant delays in sciatic axonal growth (p < 0.02) and retinal maturation (p < 0.04). The process of performing repeated fetal injections also significantly affected some retinal parameters.

CONCLUSION

Repeated fetal administration of betamethasone alters some aspects of nervous system maturation in sheep. It is premature to plan trials of repeated fetal corticosteroid therapy in humans.

Alterations of placental vascular function in asthmatic pregnancies

Asthma during pregnancy is associated with low-birthweight neonates at term but the mechanisms that cause this outcome are presently unknown. Changes in placental vascular function resulting from asthma or its treatment could contribute to altered fetal growth. We have prospectively followed women with asthma and a control group of women without asthma during their pregnancies, classified them based on asthma severity and glucocorticoid intake, and monitored fetal development and placental blood flow using Doppler ultrasound at 18 and 30 wk gestation. The placentae from these women were collected after delivery and vascular responses to dilator and constrictor agonists assessed using an in vitro placental perfusion method. At 18 wk gestation, umbilical artery flow velocity waveforms were significantly reduced in the moderate and severe asthmatic groups and in those women using high-dose inhaled glucocorticoid for the treatment of their asthma (ANOVA, p < 0.05). However, at 30 wk gestation there were no significant differences in umbilical artery flow velocity between control and asthmatic women (ANOVA, p > 0.05). Corticotropin-releasing hormone (CRH), a potent vasodilator that acts via the nitric oxide pathway, caused a dose-dependent vasodilatory response in all placentae in vitro. However, CRH-induced dilation was significantly reduced in moderate and severe asthmatics (ANOVA, p < 0.05). Vasoconstrictor responses to potassium chloride and prostaglandin F(2alpha) were reduced in placentae from moderate and severe asthmatic women (ANOVA, p < 0.05). These studies demonstrate significant differences in placental vascular function in pregnancies complicated by asthma, which may relate directly to the asthma or be a consequence of the associated glucocorticoid treatment. These changes in vascular function in asthmatic pregnancies may contribute to the low-birthweight outcome observed in this condition.

The effects of repeat doses of antenatal corticosteroids on maternal adrenal function

OBJECTIVE

The purpose of this study was to determine whether repeated doses of maternal corticosteroids suppress the maternal hypothalamic-pituitary-adrenal axis.

STUDY DESIGN

The low-dose corticotropin stimulation test (1.0 microg intravenously) was administered a median of 3 days after the last betamethasone dose to 18 pregnant women who had received at least 2 weekly courses of antenatal betamethasone and to 6 control subjects matched for gestational age who had not received antenatal corticosteroids.

RESULTS

The mean basal cortisol level was significantly depressed among women who had received betamethasone with respect to control subjects (1.9 +/- 1.5 vs 26.5 +/- 6.2 microg/dL; P <.001). The maternal cortisol level after corticotropin stimulation was significantly lower in all women who had received betamethasone (P <. 001). The mean time to attainment of peak cortisol level was significantly longer among women who had received betamethasone than among control subjects (37 +/- 6.8 vs 27.4 +/- 1.6 minutes; P <.001).

CONCLUSIONS

Repeated courses of betamethasone lead to barely detectable maternal basal cortisol levels and secondary adrenal insufficiency.

Fetal sciatic nerve growth is delayed following repeated maternal injections of corticosteroid in sheep

AIMS

A single course of prenatal corticosteroid reduces the mortality and morbidity of preterm birth. Repeated courses of prenatal corticosteroids are widely prescribed despite a lack of safety data. Repeated corticosteroids delay myelination in the ovine central nervous system at the time of preterm delivery but with catch-up at term. We aimed to evaluate their effect in the peripheral nervous system.

METHODS

Thirty date-mated ewes were administered either saline, a single injection of betamethasone, or four injections of betamethasone between 104 and 124 days' gestation, with delivery on day 125 or 145 (term = 150 days). Sciatic nerves were dissected and fixed in modified Karnovsky's fixative and prepared for light and electron microscopy to determine the proportion of myelinated axons and mean axon diameter.

RESULTS

Repeated, but not single, corticosteroid administration resulted in significant decreases in the total cross-sectional and fascicle-containing areas of the sciatic nerve, and in the mean diameter of myelinated and unmyelinated axons. Deficits persisted at term. The proportion of myelinated axons was unaffected.

CONCLUSION

Repeated prenatal corticosteroids have the capacity to affect the growth of peripheral nerve axons in sheep. Documentation of their effects in human pregnancy await randomized trials.

Retinal maturation is delayed by repeated, but not single, maternal injections of betamethasone in sheep

PURPOSE

The safety and efficacy of prescribing a single maternal course of corticosteroid during pregnancy has been documented in human trials. However, the current trend is to prescribe repeated courses of corticosteroid. We investigated an aspect of the safety of this practice in an animal model.

METHODS

Date-mated ewes received saline, single or four corticosteroid injections between days 104 and 124 of gestation (term = 150). Lambs were delivered on day 125 or 145 by caesarian section after spinal anaesthesia. Eye diameters were measured and semi-thin toluidine-blue-stained transverse sections of retinae were analysed using an Optimus Image Analysis program.

RESULTS

At 125 days, retinal measures in the ventral periphery and area centralis were significantly thinner than control (p = 0.0001). At 145 days, total eye size was significantly reduced compared with control (p = 0.03), and retinal measures in the ventral periphery (p = 0.0001), but not the area centralis (p = 0.19), remained significantly different from control.

CONCLUSION

Repeated maternal administration of corticosteroid may affect retinal maturation in the fetus.

Maternal, but not fetal, administration of corticosteroids restricts fetal growth

OBJECTIVE

Previous studies have shown that repeated doses of corticosteroids given to pregnant sheep improve postnatal lung function, but restrict fetal growth. Repeated administration of corticosteroids directly to the fetus also enhances postnatal lung function. The purpose of the present study was to investigate and characterize the relative effects on growth of repeated maternal and fetal treatments by study of body, organ, and placental weights.

METHODS

Date-bred pregnant sheep were given intramuscular betamethasone or saline to either the mother or fetus on three occasions at weekly intervals commencing at 104 days gestation, followed by cesarean section at 125 days. Twenty-two animals which had received three doses of betamethasone were compared with 21 which had received a single dose at 104 days and with 12 saline-treated controls.

RESULTS

Repeated maternal doses of betamethasone resulted in reductions in birthweight and weights of the placenta and major organs. Direct fetal injection did not affect birthweight, placental weight, placental/ birthweight ratio, or weights of the major organs with the exception of the liver.

CONCLUSIONS

Administration of repeated doses of betamethasone directly to the sheep fetus does not produce the growth-restricting effects induced by maternal administration and does not affect the placental/birthweight ratio.