Nitroglycerin as a uterine relaxant: a systematic review

Nitroglycerin: a comprehensive review in cancer therapy

Nitroglycerin (NTG) is a prodrug that has long been used in clinical practice for the treatment of angina pectoris. The biotransformation of NTG and subsequent release of nitric oxide (NO) is responsible for its vasodilatating property. Because of the remarkable ambivalence of NO in cancer disease, either protumorigenic or antitumorigenic (partly dependent on low or high concentrations), harnessing the therapeutic potential of NTG has gain interest to improve standard therapies in oncology. Cancer therapeutic resistance remains the greatest challenge to overcome in order to improve the management of cancer patients. As a NO releasing agent, NTG has been the subject of several preclinical and clinical studies used in combinatorial anticancer therapy. Here, we provide an overview of the use of NTG in cancer therapy in order to foresee new potential therapeutic avenues.

Techniques for managing an impacted fetal head at caesarean section: A systematic review

A complication arising at caesarean birth when the baby's head is deeply engaged in the pelvis and may be difficult to deliver, is known as an 'impacted fetal head'. This obstetric emergency occurs in 16% of second stage caesarean sections. Multiple techniques are described in the literature to manage the complication but there is no consensus regarding which technique results in the best maternal and neonatal outcomes. The objective of this review is to determine which technique for managing impacted fetal head at caesarean section has the best maternal and neonatal outcomes. A literature search of three electronic databases was conducted in November 2021. Studies directly comparing two methods for the management of impacted fetal head at caesarean section in the second stage were included. Systematic reviews, meta-analyses, case-control studies, and studies not fitting the search criteria were excluded. Data was extracted in Covidence and meta-analysis of the six most commonly reported outcomes was conducted using RevMan 5.4. In total, 16 studies (3344women) were included. 13 studies (2506women) compared the push method with reverse breech extraction. meta-analysis showed that risk of extension of the uterine incision, blood transfusion, bladder injury, postpartum haemorrhage, NICU admission and Apgar score <7 at 5 min were significantly higher with the push method compared with reverse breech extraction. Three studies (838women) compared the push method with Patwardhan's technique. meta-analysis of studies comparing the push method with Patwardhan's technique found no significant differences between the two groups in any of the six maternal or neonatal outcomes. Evidence derived from small, inadequately powered studies suggests reverse breech extraction is associated with better outcomes than the push method. The method which produces the best outcomes is still unknown as not all methods have been tested. Further high quality, adequately powered RCTs are warranted for definitive conclusions to be drawn and to ameliorate the paucity of evidence on how best to manage this complication.

Nitroglycerin Use in the Emergency Department: Current Perspectives

Nitroglycerin, a fast-acting vasodilator, is commonly used as a first-line agent for angina in the emergency department and to manage chest pain due to acute coronary syndromes. It is also a treatment option for other disease states such as acute heart failure, pulmonary edema, and aortic dissection. Nitroglycerin is converted to nitric oxide, a potent vasodilator, in the body, leading to venodilation at lower dosages and arteriodilation at higher dosages that results in both preload and afterload reduction, respectively. Although nitroglycerin has historically been administered as a sublingual tablet and/or spray, it is often given intravenously in the emergency department as this enables titration to effect with predictable pharmacokinetics. In this review article, we outline the indications, mechanism of action, contraindications, and adverse effects of nitroglycerin as well as review relevant literature and make general recommendations regarding the use of nitroglycerin in the emergency department.

Comparison of Nitroglycerin and Terbutaline for External Cephalic Version in Women Who Received Neuraxial Anesthesia: A Retrospective Analysis

External cephalic version is a technique that decreases the need for cesarean delivery in patients with breech presentation. Several techniques exist to increase the success of external cephalic version; however, there are no studies comparing different tocolytics in patients who also received neuraxial anesthesia. We, therefore, performed a review of 198 patients who presented for external cephalic version and compared their success rates based on the tocolytic medication utilized. The external cephalic version success rate for patients who received terbutaline was significantly higher than for those who received nitroglycerin (N [%]: 57 [65.6] terbutaline group versus 40 [36.0] nitroglycerin group; P < .001).

Primary Dysmenorrhea: Assessment and Treatment

Primary dysmenorrhea is defined as menstrual pain in the absence of pelvic disease. It is characterized by overproduction of prostaglandins by the endometrium, causing uterine hypercontractility that results in uterine muscle ischemia, hypoxia, and, subsequently, pain. It is the most common gynecological illness in women in their reproductive years and one of the most frequent causes of pelvic pain; however, it is underdiagnosed, undertreated, and even undervalued by women themselves, who accept it as part of the menstrual cycle. It has major implications for quality of life, such as limitation of daily activities and psychological stress, being one of the main causes of school and work absenteeism. Its diagnosis is essentially clinical, based on the clinical history and normal physical examination. It is important to exclude secondary causes of dysmenorrhea. The treatment may have different approaches (pharmacological, non-pharmacological and surgical), but the first line of treatment is the use of nonsteroidal anti-inflammatory drugs (NSAIDs), and, in cases of women who want contraception, the use of hormonal contraceptives. Alternative treatments, such as topical heat, lifestyle modification, transcutaneous electrical nerve stimulation, dietary supplements, acupuncture, and acupressure, may be an option in cases of conventional treatments' contraindication. Surgical treatment is only indicated in rare cases of women with severe dysmenorrhea refractory to treatment.

Obstetric and Anesthetic Approaches to External Cephalic Version

Breech presentation is the most common abnormal fetal presentation and complicates approximately 3% to 4% of all pregnancies. External cephalic version (ECV) should be recommended to women with a breech singleton pregnancy, if there is no maternal or fetal contraindication. ECV increases the chance of cephalic presentation at the onset of labor and decreases the rate of cesarean delivery by almost 40%. The success rate of ECV is approximately 60%. Review of the risks and benefits for performing an ECV and for both the timing of ECV and the number of attempts should be should be discussed with the patient.

Maternal plasma nitric oxide metabolites and cervical length assessment in predicting the tocolytic therapy in preterm labor in Isfahan

Background:

Preterm labor (PTL) is the main challenge in prenatal health care, leads to high rate of mortality and increases cost of health services. To evaluate the preterm delivery (PTD)-related risk factors, we decided to measure nitrite oxide metabolites and cervical length (CL) as the diagnostic and predictive tools for PTD in women and response to tocolytic therapy.

Materials and Methods:

In this case–control study, sixty women of 18–35 years with first pregnancy during the 24–34 gestational weeks with PTL in case group admitted to the delivery section of Beheshti Hospital, Isfahan, Iran were included. Sixty women in control group have the same specifications. NO and CL level were assessed, and the collected data were analyzed by SPSS software, version 20 and MedCalc software, version 15.1.

Results:

The two groups were similar regarding maternal and gestational age (P > 0.05). Lower level of NO was observed in PTL women with a mean of 35.30 ± 8.27 μmol/L compared to the normal gestation group with a mean of 39.05 ± 10.17 μmol/L (P = 0.035). In addition, the diagnostic accuracy of both PTL-predicting factors was determined (NO ≤31, sensitivity 99.7%, specificity 82.5% and CL ≤22, sensitivity 80%, specificity 99.9%).

Conclusion:

As the previous investigations stated, it can be claimed that NO might be the reliable marker for predicting the PTL, and administration of NO synthesis could be a candidate for the future therapeutic target.

The effects of sequential use of oxytocin and sublingual nitroglycerin in the cases of retained placenta

OBJECTIVES

To evaluate the effects of adding sublingual nitroglycerin to oxytocin, for delivery of retained placenta after vaginal delivery.

METHOD

The study was performed as a placebo controlled clinical trial on women who did not finish delivering placenta after 30 min of active management of the third stage of labor. In case group, 1 mg nitroglycerin and in the control group, placebo was prescribed sublingually.

RESULTS

In total, 80 women finished the study. The number of manual removal of placenta did not show significant difference between the two groups [25 women (62.5%) in the case and 30 women (75%) in the control group, p = 0.335]. There was no significant difference between the two groups according to duration of the third stage of labor, hemoglobin index, decline in HB index >30% and maternal vital signs after treatment. There was no significant difference between the two groups according to adverse effects [eight women (20%) in the case group and four (10%) in the control group (p = 0.348)].

CONCLUSION

The sequential use of oxytocin and sublingual nitroglycerin could not lead to delivery of more placentas and did not reduce the necessity of manual removal of placenta in comparison with placebo.

Effect of a physiotherapy program in women with primary dysmenorrhea

OBJECTIVE

To evaluate the efficacy of a physiotherapy program for relieving symptoms of primary dysmenorrhea among Mexican women.

STUDY DESIGN

This was a single-center, prospective, experimental, parallel group, randomized controlled trial. This cross-sectional study was performed at the Universidad Politécnica de Pachuca, Hidalgo, Mexico. Female patients with primary dysmenorrhea, age of 18-22 years; pain intensity from 4 to 10cm on a Visual Analogue Scale (VAS); and sedentary lifestyle were included. The patients were then randomized to receive a physiotherapy program for three months or to no intervention program. The physiotherapy program consisted of overall stretching, specific stretches, Kegel exercises, jogging, and relaxation exercises. Patient evaluations of symptomatology and pain intensity were recorded basally and throughout for three menstrual periods. The data were entered into a computerized database for descriptive and inferential statistical analyses.

RESULTS

A per-protocol population of eighty three women with a mean age of 20.2±1.8 years underwent the physiotherapy program, and seventy seven participants with a mean age of 20.4±1.2 years received no treatment. The participant assessments of pain on the VAS during the second and the third menstrual cycles demonstrated a significant reduction in the treatment group (p<0.05) compared with the control group.

CONCLUSIONS

The results showed that strengthening, stretching and muscle relaxation techniques, in addition to jogging, are effective for reducing dysmenorrheic symptoms when they are regularly performed.

Antenatal exposure to indomethacin increases the risk of severe intraventricular hemorrhage, necrotizing enterocolitis, and periventricular leukomalacia: a systematic review with metaanalysis

OBJECTIVE

The purpose of this study was to provide an updated summary of the literature regarding the effects of tocolysis with indomethacin on neonatal outcome by systematically reviewing previously and recently reported data.

STUDY DESIGN

All previously reported studies pertaining to indomethacin tocolysis and neonatal outcomes along with recently reported data were identified with the use of electronic databases that had been supplemented with references that were cited in original studies and review articles. Observational studies that compared neonatal outcomes among preterm infants who were exposed and not exposed to indomethacin were included in this systematic review. Data were extracted and quantitative analyses were performed on those studies that assessed the neonatal outcomes of patients that received antenatal tocolysis with indomethacin.

RESULTS

Twenty-seven observational studies that met criteria for systematic review and metaanalysis were identified. These studies included 8454 infants, of whom 1731 were exposed to antenatal indomethacin and 6723 were not exposed. Relative risks with 95% confidence intervals were calculated for dichotomous outcomes with the use of random and fixed-effects models. Metaanalysis revealed no statistically significant differences in the rates of respiratory distress syndrome, patent ductus arteriosus, neonatal mortality rate, neonatal sepsis, bronchopulmonary dysplasia, or intraventricular hemorrhage (all grades). However, antenatal exposure to indomethacin was associated with an increased risk of severe intraventricular hemorrhage (grade III-IV based on Papile's criteria; relative risk, 1.29; 95% confidence interval, 1.06-1.56), necrotizing enterocolitis (relative risk, 1.36; 95% confidence interval, 1.08-1.71), and periventricular leukomalacia (relative risk, 1.59; 95% confidence interval, 1.17-2.17).

CONCLUSION

The use of indomethacin as a tocolytic agent for preterm labor is associated with an increased risk for severe intraventricular hemorrhage, necrotizing enterocolitis, and periventricular leukomalacia.

Comparison between nitroglycerin dermal patch and nifedipine for treatment of preterm labor: a randomized clinical trial

OBJECTIVE

Preterm labor and delivery are of the most important complications of pregnancy and have a major role in neonatal mortality and morbidity. Management of preterm labor and prevention from preterm delivery in order to lower these risks have always been under serious concern. The purpose of this study was to compare the effect of nifedipine and nitroglycerin (NG) dermal patch for taking control of preterm labor.

STUDY DESIGN

The study was performed as a randomized clinical trial on women who had been admitted in the hospital diagnosed with preterm labor. In one group, the NG dermal patch and in the other group, nifedipine was prescribed. Then the women of the two groups were followed up to delivery and were compared according to arrest of labor for 2 h, 48 h, 7 days, gestational age at the time of delivery and their adverse effects. The primary outcome was to postpone delivery for 48 h in order to have enough time for prescribing corticosteroids

RESULT

The women of the two groups did not have any significant difference according to age, body mass index, primary Bishop Score, gestational age at the time of tocolytic therapy, history of abortion, vaginal or cesarean delivery and preterm labor. In more women in the NG group, delivery was postponed for 2 h (59 (98.3%) vs 48 (80%), P=0.001), for 48 h (52 women (86.7%) vs 41(68.3%), P=0.016) and also for 7 days (47 (78.3%) vs 37 (61.7%), P=0.046), than the women in the nifedipine group. Gestational age at the time of delivery was higher in the NG group (35.6±1.9 vs 34.3±2.05 weeks, P=0.155), however, it was not statistically significant. Apgar score of minute 5, (P=0.03) and neonatal weight (P=0.04), were more and cesarean deliveries, neonatal intensive care unit (NICU) admission and duration of NICU stay were less in the NG group. Adverse effects were similar, minimal and negligible in both groups.

CONCLUSION

The NG patch is a more effective method for preterm labor control than nifedipine with regard to minimal side effects.

Transdermal nitroglycerin for the treatment of preterm labor: a systematic review and metaanalysis

OBJECTIVE

The purpose of this study was to evaluate the efficacy and safety of transdermal nitroglycerin as a tocolytic agent in women with preterm labor.

STUDY DESIGN

We conducted a systematic review and metaanalysis of randomized controlled trials.

RESULTS

Thirteen studies were included (1302 women) comparing transdermal nitroglycerin vs placebo (2 studies; n = 186); β2-adrenergic receptor agonists (9 studies; n = 1024); nifedipine (1 study; n = 50); and magnesium sulfate (1 study; n = 42). There were no significant differences between transdermal nitroglycerin and placebo for delivery within 48 hours of the initiation of treatment or at <28, <34, or <37 weeks of gestation, adverse neonatal outcomes, and neurodevelopmental status at 24 months of life. Nevertheless, 1 study found a marginally significant reduction in the risk of a composite outcome of major neonatal morbidity and perinatal death (3/74 [4.1%] vs 11/79 [13.9%]; relative risk, 0.29; 95% confidence interval, 0.08-1.00). When compared with β2-adrenergic receptor agonists, transdermal nitroglycerin was associated with a significant reduction in the risk of preterm birth at <34 and <37 weeks of gestation, admission to the neonatal intensive care unit, use of mechanical ventilation, and maternal side effects. There were no significant differences between transdermal nitroglycerin and nifedipine and magnesium sulfate in delivery within 48 hours of treatment and pregnancy prolongation, respectively. Overall, women who received transdermal nitroglycerin had a higher risk of headache.

CONCLUSION

Although transdermal nitroglycerin appears to be more effective than β2-adrenergic receptor agonists, the current evidence does not support its routine use as a tocolytic agent for the treatment of preterm labor. Further double-blind placebo-controlled trials are needed.

Anaesthesiological considerations on tocolytic and uterotonic therapy in obstetrics

AIM

Significant side effects of tocolytic and uterotonic substances may be of concern to the anaesthesiologist. Recently, new drugs have been introduced having less side effects for both the mother and the neonate.

METHODS

A literature search was undertaken mainly focusing on meta-analyses, to review the possible side effects that might affect the course of anaesthesia and to suggest which precautions should be considered to prevent the occurrence of significant interactions with anaesthetic manipulations and drugs.

RESULTS

Magnesium sulphate has a proven benefit in lowering systolic blood pressure and preventing the occurrence of eclampsia, but not as a tocolytic. beta-adrenergic agonists are being abandoned due to the availability of tocolytic agents causing less side effects. Calcium channel blockers (CCB) are frequently used but can cause major maternal cardiovascular complications. Nitroglycerin seems to be appreciated as an acute tocolytic rather than a routine substance during pre-term labour. Cyclo-oxygenase-2 inhibitors are still under investigation but their tocolytic benefit is questionable mainly due to foetal side effects. Atosiban is considered the first-choice tocolytic. With respect to oxytocic drugs, oxytocine, prostaglandines and methylergometrine may all cause serious side effects especially when combined. The cardiovascular side effects of prostaglandins and methylergometrine can be life-threatening. Both oxytocin and carbetocin have a rather low risk for maternal complications.

CONCLUSION

Atosiban and CCB are at least as effective tocolytic agents as beta-mimetics but have significantly less side effects. Magnesium sulphate can cause neuromuscular blockade, especially when combined with CCB. Concerning oxytocic agents, short-acting oxyctocin and long-acting carbetocin have the least side effects as compared with prostaglandins and methylergometrine.

Clinical use of nitric oxide donors and L-arginine in obstetrics

Nitric oxide (NO) is a free radical that plays a fundamental role in human physiology, being involved in the homeostasis of different functions. In obstetrics this molecule is determinant in the physiology of labor and cervical ripening; it possibly plays a fundamental role in the etiology of preeclampsia and intrauterine growth restriction, and it could also be utilized in view of its ability to induce smooth muscle relaxation. Several clinical trials have ascertained the ability of the topical application of NO donors to promote cervical ripening, and also labor induction. There is much less evidence on the use of NO donors in the vascular complications of pregnancy, either as prophylactics or therapeutic agents. Due to the capacity of NO to promote relaxation of smooth muscle, NO donors have been employed as tocolytics with performance similar to other agents. Moreover, although anecdotal, the experience of sudden uterine relaxation using NO donors in obstetric emergencies remains of great clinical value.

Chronic pelvic pain in women of childbearing age

PURPOSE OF REVIEW

The purpose of this article is to summarize new findings in the area of chronic pelvic pain in women of childbearing age.

RECENT FINDINGS

Particular attention over the past few years has been paid to the multidisciplinary approach in diagnosing and treating chronic pelvic pain, because it is common knowledge that different medical specialties very often deal with patients affected by this condition.

SUMMARY

A classification of chronic pelvic pain is presented, along with the recommended evaluation, diagnostic investigations, and treatment of this condition, based on recent reports in the literature.

Primary dysmenorrhea: advances in pathogenesis and management

Primary dysmenorrhea is painful menstrual cramps without any evident pathology to account for them, and it occurs in up to 50% of menstruating females and causes significant disruption in quality of life and absenteeism. Current understanding implicates an excessive or imbalanced amount of prostanoids and possibly eicosanoids released from the endometrium during menstruation. The uterus is induced to contract frequently and dysrhythmically, with increased basal tone and increased active pressure. Uterine hypercontractility, reduced uterine blood flow, and increased peripheral nerve hypersensitivity induce pain. Diagnosis rests on a good history with negative pelvic evaluation findings. Evidence-based data support the efficacy of cyclooxygenase inhibitors, such as ibuprofen, naproxen sodium, and ketoprofen, and estrogen-progestin oral contraceptive pills (OCPs). Cyclooxygenase inhibitors reduce the amount of menstrual prostanoids released, with concomitant reduction in uterine hypercontractility, while OCPs inhibit endometrial development and decrease menstrual prostanoids. An algorithm is provided for a simple approach to the management of primary dysmenorrhea.

Recent pharmacological advances in the treatment of preterm membrane rupture, labour and delivery

Preterm delivery (before 37 completed weeks of gestation) is the major determinant of infant mortality. In women with a previous preterm birth associated with bacterial vaginosis, prophylactic antibiotics (e.g., metronidazole) reduce the risk of preterm birth and low birth weight. Trichomonas vaginalis increases the risk of preterm delivery, but metronidazole is not beneficial for this and may even be detrimental. Antibiotic use (e.g., erythromycin) prolongs pregnancy in late premature rupture and has health benefits for the neonate. However, antibiotics are probably not useful in preterm labour. Intramuscular 17alpha-progesterone and vaginal progesterone reduce the rate of preterm labour in high-risk pregnancies, including previous spontaneous preterm delivery. Magnesium sulfate, beta2-adrenoceptor agonists and the oxytocin-receptor antagonist, atosiban, are effective in reducing uterine contractions short-term, but there is little evidence that this leads to improved outcomes for the neonate. However, tocolysis with calcium-channel blockers does seem to lead to better outcomes for the neonate. Fetal side effects, such as ductus arteriosus constriction and impaired renal function, are associated with the inhibition of prostaglandin synthesis with indomethacin. New approaches and more effective drugs are required in the treatment of preterm delivery.

Difficult delivery of the impacted fetal head during cesarean section: intraoperative disengagement dystocia

Cesarean section is commonly perceived as a simple and safe alternative to difficult vaginal birth. However, several trends in obstetrical practice may act in concert to cause impaction of the fetal head during the second stage of labor or, more commonly, following failed instrumental delivery. Subsequently, difficult and potentially traumatic disengagement of the deeply wedged head during cesarean section occurs. The maneuvers to disengage the wedged head include pushing (bimanual or by an assistant) the head through the vagina or, alternatively, pulling the infant's feet through the uterine incision. Although both methods may cause serious maternal and neonatal complications, available data seem to favor the pulling method and better outcome seems to depend on adequate uterine relaxation, the patient's position during operation, and special attention to the uterine incision. More data are needed to establish the frequency and extent of intraoperative disengagement dystocia and to determine the management protocol that carries the lowest risk in such circumstances.

Randomized comparison of intravenous nitroglycerin and subcutaneous terbutaline for external cephalic version under tocolysis

OBJECTIVE

The purpose of this study was to compare the efficacy and safety of intravenous nitroglycerin with that of subcutaneous terbutaline as a tocolytic agent for external cephalic version at term.

STUDY DESIGN

We performed a prospective randomized trial. Patients between 37 and 42 weeks of gestation were assigned randomly to receive either 200 microg of intravenous nitroglycerin therapy or 0.25 mg of subcutaneous terbutaline therapy for tocolysis during external cephalic version. The rate of successful external cephalic version and side effects were compared between groups.

RESULTS

Of 59 randomly assigned patients, 30 patients received intravenous nitroglycerin, and 29 patients received subcutaneous terbutaline. The overall success rate of external cephalic version in the study was 39%. The rate of successful external cephalic version was significantly higher in the terbutaline group (55% vs 23%; P = .01). The incidence of palpitations was significantly higher in patients who received terbutaline therapy (17.2% vs 0%; P = .02), as was the mean maternal heart rate at multiple time periods.

CONCLUSION

Compared with intravenous nitroglycerin, subcutaneous terbutaline was associated with a significantly higher rate of successful external cephalic version at term.

Sublingual nitroglycerin versus placebo as a tocolytic for external cephalic version: a randomized controlled trial in parous women

OBJECTIVE

The purpose of this study was to evaluate the efficacy of sublingual nitroglycerin as a tocolytic agent for external cephalic version in parous women.

STUDY DESIGN

A double-blinded randomized controlled trial was performed. Patients with parity of >or=1 at 36 to 40 weeks of gestation who were eligible for external cephalic version were included. Patients were randomized to receive either two sublingual sprays of 400 mug of nitroglycerin or two sprays of placebo 3 minutes before the trial of external cephalic version. Rates of successful external cephalic version and side effects were compared between groups.

RESULTS

Of 99 patients in the study, 50 patients received sublingual nitroglycerin, and 49 patients received placebo. There were no differences in maternal age, gestational age, estimated fetal weight, amniotic fluid index, and placental location between the two groups. The success rate of external cephalic version was 48% in the nitroglycerin group compared with 63% in the placebo group (P=.13). There was a higher incidence of headaches in the nitroglycerin group (42% vs 4%, P<.001).

CONCLUSION

Sublingual nitroglycerin was associated with a higher rate of headache and did not improve the rate of successful external cephalic version.

Steady-state maternal and fetal plasma concentrations of glyceryl trinitrate (GTN) in the preterm sheep

The administration of glyceryl trinitrate (GTN; nitroglycerin) is increasing during preterm pregnancies, yet its disposition and, importantly, the extent of fetal exposure remain to be elucidated. When used as a tocolytic (pharmacological agent that stops uterine contractions), it is administered transdermally (24–48 h). Here, we quantified the maternal and fetal steady-state plasma concentrations of maternal intravenous GTN in preterm sheep and continuously monitored maternal and fetal vascular parameters to observe possible dose-dependant vascular effects. Preterm (120 days gestation) pregnant sheep (n = 6) were instrumented with maternal femoral arterial (MA) and venous (MV) and fetal femoral arterial (FA) and umbilical venous (UV) polyethylene blood-sampling catheters. During maternal GTN infusion (3.0 µg·kg–1·min–1, 60-min duration) the steady-state GTN concentrations ([GTN]) were as follows: MA, 98.6 ± 9.0 nM; UV, 17.4 ± 7.6 nM; and FA, <5 nM. There were no changes in maternal and fetal mean arterial pressure and heart rate or in uterine activity. Overall, the steady-state [GTN] was established by 5 min, and the UV/MA ratio of [GTN] was 0.18. The FA [GTN] (<5 nM) indicates that the fetus cleared essentially all GTN in the UV, and the maternal and fetal heart rate and mean arterial pressure appear to be independent of maternal GTN infusion.Key words: nitroglycerin, pharmacokinetics, maternal-fetal exchange, pregnancy, cardiovascular.