Intra-amniotic Pressure Research Articles

Intraamniotic sealing of fetoscopic membrane defects in ex vivo and in vivo sheep models using an integrated semirigid bioadhesive patch

Preterm prelabor rupture of membranes is the most frequent complication of fetoscopic surgery. Strategies to seal the membrane defect created by fetoscopy have been attempted with little success. We previously developed an integrated semirigid bioadhesive patch composed of silicone and hydroxypropyl methylcellulose that achieved ex vivo sealing of membrane defects. To evaluate the feasibility of the insertion of our integrated semirigid bioadhesive patches using a fetoscopic technique and to test the adhesion in ex vivo human membranes and in an in vivo ovine model. An experimental study involving 2 experiments: (1) ex vivo-human fetal membranes were mounted in a custom-designed model with saline solution simulating intraamniotic pressure. The insertion of 2 different bioadhesive patches made of silicone-hydroxypropyl methylcellulose and silicone-polyurethane-hydroxypropyl methylcellulose was performed through a 12-Fr cannula mimicking fetoscopic surgery technique. The experiment was repeated 10 times with membranes from different donors. Measures included insertion time, successful insertion, and adhesion at 5 minutes; (2) in vivo-16 patches of silicone-hydroxypropyl methylcellulose were inserted by fetoscopy in the amniotic cavity of pregnant sheep (4 bioadhesives per animal, in 4 ewes). Measures included successful insertion, adhesion at 5 minutes, and adhesion at the end of surgery. In the ex vivo insertion study, there was no difference in the insertion time between silicone-hydroxypropyl methylcellulose and silicone-polyurethane-hydroxypropyl methylcellulose patches (P=.49). Insertion was successful in all cases, but complete adhesion at 5 minutes was superior for silicone-hydroxypropyl methylcellulose (P=.02). In the in vivo study, insertion of silicone-hydroxypropyl methylcellulose by fetoscopy was feasible and successful in all cases, and no complications were reported. Adhesion persisted at 5 minutes and at the end of the surgery in 68.8% and 56.3% of the patches, respectively. We describe the feasibility of deploying through a fetoscopic trocar a semirigid silicone-hydroxypropyl methylcellulose patch that seals fetal membranes after an invasive fetal procedure. The results warrant further research for improving long-term adhesion and developing a clinically applicable system.

Changes in the Intra-Amniotic Pressure following Transabdominal Amnioinfusion during Pregnancy

Objective: The aim of the article was to investigate the changes in intra-amniotic pressure following transabdominal amnioinfusion during pregnancy. Design: This retrospective study included 19 pregnant women who underwent transabdominal amnioinfusion during pregnancy to relieve umbilical cord compression and improve the intrauterine environment or to increase the accuracy of ultrasonography. Materials and Methods: We measured and analyzed the changes in intra-amniotic pressure, single deepest pocket, and the amniotic fluid index before and after amnioinfusion. We also determined the incidence of maternal or fetal adverse events, such as preterm premature rupture of membranes, preterm delivery, fetal death within 48 h, placental abruption, infection, hemorrhage, and peripheral organ injury. Results: A total of 41 amnioinfusion procedures were performed for 19 patients. The median gestational age during the procedure was 24.3 weeks. The median volume of the injected amniotic fluid was 250 mL. The median single deepest pocket and amniotic fluid index after amnioinfusion were significantly higher than those before amnioinfusion (4.0 cm vs. 2.65 cm; p < 0.001 and 13.4 cm vs. 6.0 cm; p < 0.001). However, the median (range) intra-amniotic pressure after amnioinfusion was not significantly different compared to that before amnioinfusion (11 mm Hg vs. 11 mm Hg; p = 0.134). Maternal or fetal adverse events were not observed following amnioinfusion. Conclusion: Intra-amniotic pressure remained unchanged following amnioinfusion. The complications associated with increased intra-amniotic pressure are not likely to develop if the amniotic fluid index and/or single deepest pocket remains within the normal range after amnioinfusion. Studies of groups with and without complications are warranted to clarify the relationship between the intra-amniotic pressure and incidence of complications.

Effect of intra‐amniotic fluid pressure from polyhydramnios on cervical length in patients with twin–twin transfusion syndrome undergoing fetoscopic laser surgery

To determine the relationship between intra-amniotic pressure and cervical length (CL) in patients with twin-twin transfusion syndrome (TTTS) undergoing fetoscopic laser photocoagulation (FLP), and to identify pre- or intraoperative factors associated with increased intra-amniotic pressure in this population. This was a prospective cohort study of patients undergoing FLP for TTTS. Exclusion criteria were triplet or higher-order gestation and prior cervical cerclage, amnioreduction or FLP procedure. CL was assessed using preprocedure transvaginal ultrasound. Intra-amniotic pressure measurements were obtained on initial placement of the trocar into the amniotic cavity, using a direct hydrostatic pressure gauge. The relationship between intra-amniotic pressure and CL was assessed using multivariate linear regression analysis, including relevant preoperative and intraoperative variables. In total, 283 pregnancies met the inclusion criteria. Quintero stage of TTTS was I in 33 pregnancies, II in 88, III in 150 and IV in 12. Mean gestational age (GA) at FLP was 20.7 ± 3 weeks. Mean intra-amniotic pressure was 23.1 ± 9 mmHg. On unadjusted linear regression analysis, there was no significant association between intra-amniotic pressure and preoperative CL (P = 0.24) or GA at delivery (P = 0.22). On multivariate analysis, the factors associated significantly with intra-amniotic pressure were: number of prior term deliveries (P = 0.03), recipient maximum vertical pocket (P < 0.0001), Quintero stage IV (P = 0.01) and type of anesthesia (sedation vs general anesthesia; P = 0.01). In pregnancies with TTTS, intra-amniotic pressure is not associated with CL or GA at delivery. This novel finding suggests that cervical shortening in this population is not mechanically driven. Copyright © 2019 ISUOG. Published by John Wiley & Sons Ltd.

Relationship between higher intra-amniotic pressures in polyhydramnios and maternal symptoms

ObjectivesOur study aimed to analyze the differences in intra-amniotic pressures in patients with polyhydramnios with and without symptoms. Study designWe recruited patients with pregnancies in which amnioreduction was performed for polyhydramnios in the Department of Fetal-Maternal Medicine at Nagara Medical Center between April 2017 and August 2018. Amnioreduction was performed for severe polyhydramnios with maternal symptoms [symptomatic group] or polyhydramnios without maternal symptoms [asymptomatic group] such as abdominal distension, dyspnea, or threatened premature labor. We measured the intra-amniotic pressure after every 200 ml volume reduction during the amnioreduction. ResultsA total of 27 patients who underwent amnioreduction were classified into symptomatic (66.7%, 18/27) and asymptomatic (33.3%, 9/27) groups. Gestational age, amniotic fluid index at the time of amnioreduction, and the volume of amniotic fluid removed were not significantly different between the symptomatic and asymptomatic groups [median 32.4 weeks vs. 33.1 weeks, median 38.0 cm vs. 39.0 cm, and median 1500 ml vs. 2500 ml, respectively]. However; the intra-amniotic pressure before amnioreduction was significantly higher in the symptomatic group than in the asymptomatic group [median 15.0 mmHg (range, 10–27) vs. 10.0 mmHg (range, 6.0–13); p < 0.005]. After amnioreduction, these pressures decreased significantly to median 9.0 mmHg (range, 5.0–13) (p < 0.001) in the symptomatic and 7.0 mmHg (range, 4.0–11) (p < 0.05) in the asymptomatic group. The median intra-amniotic pressure gradually decreased and reached a plateau during the amnioreductions in both groups. ConclusionsWith polyhydramnios, the intra-amniotic pressure was significantly higher in the symptomatic group than in the asymptomatic group. Therefore, uterine pressure tolerance might vary according to the individual. In addition, intra-amniotic pressure monitoring might enhance the safety during amnioreduction procedures to avoid drastic and potentially harmful pressure changes.

When should foetal pH measurements be performed after a prolonged deceleration? An experimental study in a fetal sheep model

ObjectiveThe aim of fetal heart rate monitoring during labour is to identify and prevent foetal distress, but its evaluation is not perfect. Fetal scalp blood sampling for pH measurement is one of the second-line methods of monitoring when fetal heart rate is classified as suspicious. This study aims to determine when pH testing should be performed after a prolonged deceleration. Study designThis was an experimental study in a fetal sheep model. A partial umbilical cord occlusion was performed for seven minutes followed by a recuperation period of 30 min. Hemodynamic parameters (heart rate, mean blood pressure and intra-amniotic pressure) and blood gases were recorded before occlusion (T0), during occlusion (T4), just after the end of occlusion (T7), and then 10, 20 and 30 min after occlusion (T17, T27 and T37 respectively). ResultsTen experiments were carried out. During partial cord occlusion, the fetal pH decreased significantly to acidosis. After a prolonged deceleration with fetal acidosis, the pH recovered to a normal value, defined by a pH greater than or equal to 7.25, after 20 min of recuperation. ConclusionAfter a prolonged deceleration, fetal pH normalizes between 20 and 30 min thereafter. Thus, if a foetal blood sample is indicated, this delay must be respected in order to avoid inducing an unnecessary intervention decision.

Non-invasive emergent cerclage using a plastic sling: case series

Cervical incompetence represents a controversial problem for the modern obstetrician. Treatment modalities since its description have changed with time. Shirodkar and McDonald cerclage techniques have remained the mainstay in the...

Prediction of pulmonary hypoplasia in mid‐trimester preterm prelabor rupture of membranes: research or clinical practice?

Prediction of pulmonary hypoplasia in mid‐trimester preterm prelabor rupture of membranes: research or clinical practice?

Comparison of the effects of sevoflurane and isoflurane anesthesia on the maternal-fetal unit in sheep

The aim of this study was to determine the hemodynamic and blood gas effects of inhalational anesthetics on the maternal-fetal sheep unit. The principal hypothesis, tested in chronically instrumented near-term pregnant ewes, was that sevoflurane anesthesia may be safe and useful for the mother and fetus during pregnancy, compared with isoflurane. Six chronically instrumented pregnant and 3 nonpregnant ewes were tested repeatedly to establish the minimum alveolar concentration (MAC) for sevoflurane and isoflurane to be used in the hemodynamic and blood gas studies. Progressively increasing concentrations of sevoflurane or isoflurane in oxygen were administered to 12 pregnant ewes. Uterine blood flow, maternal and fetal heart rates, blood pressure, arterial blood gases, and intra-amniotic pressure were subsequently measured. The MAC of sevoflurane was 1.52 +/- 0.1 15% and 1.92 +/- 0.17% in pregnant and nonpregnant ewes, respectively; while the MAC of isoflurane in the pregnant and nonpregnant sheep was 1.02 +/- 0.12% and 1.42 +/- 0.19%, respectively. In both the sevoflurane and isoflurane groups, changes in maternal and fetal blood gases were minimal during exposure to low-dose (0.5-1.0 MAC) inhaled concentrations. Although uterine blood flow was maintained and the fetus remained well oxygenated at higher concentrations of both agents (2.0 MAC of either agent), the agents produced decreases in maternal and fetal arterial pressure. A "low-dose" concentration (0.5-1.0 MAC) of sevoflurane may be safe and useful for both mother and fetus during near-term pregnancy. However, a high concentration (1.5-2.0 MAC) of sevoflurane or isoflurane may induce hemodynamic instability in the mother and fetus when administered.

Increased maternal intraabdominal pressure alters the contractile properties of fetal rabbit bladder

Background/Purpose Increased intraabdominal pressure (IAP) causes impairment of urine flow by compressing the urine-transporting structures and leads to development of various types of anatomical and functional abnormalities in the urinary system. An intrauterine experiment was conducted to determine the relationship between IAP and intraamniotic pressure (IAMNP) and the effects of increased IAMNP on the contractile properties of fetal bladder in the rabbit model. Materials and Methods Fourteen time-mated pregnant rabbits were used. A preliminary study (n = 5, 20-day gestation) was performed to determine the relation between IAP and IAMNP. Intraabdominal pressure and IAMNP were recorded through an intraperitoneal catheter and 2 intraamniotic transducers, respectively. Basal IAP and IAMNP were recorded. Then, IAP was increased for 4 cm H 2O in each subsequent 30-minute period until reaching 20 cm H 2O. Control (n = 5) and experiment (n = 4) group animals underwent intraperitoneal catheter placement in the 15th day of gestation. Intraabdominal pressure was increased by intraperitoneal air insufflations from 20th day to term in the experiment group. At term, the fetal bladders were excised and the contractile activity was then recorded isometrically. Electrical field stimulation was applied, and contractile responses to carbachol and high potassium (20 mmol/L KCl) were also evaluated. Results A strong relationship was found between IAMNP and IAP and defined as IAMNP = IAP × 0.8 + 2.0 ( R 2 = 0.816, P = .000). Increased IAP did not change basal rhythmic activity but resulted in frequency-related electrical field stimulation responses being higher contractility responses for frequencies below 10 Hz ( P < .05) and similar responses at and above 10 Hz. Bladders imposed to elevated IAP displayed greater sensitivity to carbachol with a shift to the left in the concentration-response curve. High potassium–induced contractions had a shorter rise time ( P < .05) but similar contraction amplitudes and half decay times in bladders imposed to increased IAP. Conclusion Intraamniotic pressure is affected by IAP in pregnant rabbits in accordance with an equation (IAMNP = IAP × 0.8 + 2.0). Increased IAMNP changes contractile properties of the fetal rabbit bladder without affecting spontaneous activity and shortens the rise time of high potassium–induced contractions. Increased IAMNP also results in cholinergic hypersensitivity in fetal bladders. These results may explain the mechanism of dysfunctional voiding and abnormal bladder function observed in conditions in which IAP and/or IAMNP are elevated.

Fetal hydrocephalus, intrauterine diagnosis and therapy considerations: an experimental rat model

Fetal hydrocephalus is induced by a single intraperitoneal injection of 8 mg/kg 6-aminonikotinamide (6-AN), a niacinamide antagonist, in Sprague-Dawley rats on day 13 of gestation. Laparotomy was carried out in some rats 3, 6, 7 and 8 days after the intraperitoneal injection. The fetuses were collected by uterotomy and fixed in a formalin solution after measuring head circumference and body length for further histological investigations. The ventricular areas and volumes of the lateral ventricles were measured using a computer morphometric technique after all fetuses were serially sectioned sagittally or coronally. Furthermore, 8 maternal rats (4 treated with 6-AN and 4 controls) were used for ultrasound investigation. The fetal ventricular system and the central canal were demonstrated and compared by transabdominal ultrasound in the 6-AN and control groups. On day 19 of gestation the cerebrospinal fluid (CSF) was drained in some fetuses for 18 h through a thin micro-catheter, which was inserted into the lateral ventricle. In some other fetuses the intracranial pressure (ICP) and the intra-amniotic pressure (IAP) were measured after Doppler sonography of the cerebral blood flow (CBF). These measurements were carried out using a transuterine approach following the laparotomy. Hydrocephalus was produced due to the closure of all outlets of the fourth ventricle. Macrocephalus was clear on day 17 (4 days after 6-AN injection). The entire ventricular system was dilated, including the aqueduct and foramen of Monro, and cerebellar hypoplasia was revealed. Increased ICP in 6-AN fetuses was associated with decreasing CBF. The cerebral mantel was better developed after CSF drainage. The intra-amniotic pressure was increased in all pregnant rats and was either similar to or higher than ICP.

Twin‐to‐twin transfusion syndrome: treatment with endoscopic laser surgery or serial amnio‐reduction?

Twin‐to‐twin transfusion syndrome: treatment with endoscopic laser surgery or serial amnio‐reduction?

Effects of amniodistention with carbon dioxide on fetal acid-base status during fetoscopic surgery in a sheep model.

Because the data from previous experiments on the fetal effects of carbon dioxide (CO2) amniodistention in endoscopic fetal surgery are conflicting, we set out to evaluate the fetal acid-base status during CO2 amniodistention, with or without maternal hyperventilation, using a sheep model for endoscopic surgery. We assigned 26 pregnant ewes undergoing amniodistention with CO2 (4-5 mmHg intraamniotic pressure) to one of the following three groups: group I had fetal surgery + no maternal hyperventilation (n = 10); group II had fetal surgery + maternal hyperventilation (n = 10); group III had no fetal surgery + maternal hyperventilation (n = 6). Hyperventilation kept CO2 at 29-31 mmHg; in its absence, pCO2 ranged from 38 to 41. Fetal surgery consisted of fetoscopic tracheal clipping. Maternal blood pressure (mean, 98/69 mmHg) and heart rate (mean, 72 bpm) were kept at values comparable to human pregnancy. Fetal and maternal blood gas measurements were taken every 15 min during 1 h of amniodistention. The ranges for baseline mean fetal pCO2 (mmHg) and pH were 51-55 and 7.24-7.25, respectively, in all study groups. After 1 h of amniodistention, mean +/- SEM values of fetal pCO2 and pH were 88 +/- 3 and 7.06 +/- 0.03 in group I, 69 +/- 4 and 7.13 +/- 0.02 in group II, and 71 +/- 5 and 7.14 +/- 0.04 in group III, respectively. Therefore, maternal hyperventilation attenuated but could not prevent significant fetal hypercarbia and acidosis. Fetal surgical manipulation had no effect on these observations. CO2 amniodistention should not be considered for clinical practice until ways of preventing its effects on the fetal acid-base status can be demonstrated.

The placental transfer and fetal effects of levobupivacaine, racemic bupivacaine, and ropivacaine.

The purposes of this study were to assess the effects of levobupivacaine on uterine blood flow and fetal well-being and to compare its placental transfer with that of bupivacaine and ropivacaine. After a control period, pregnant ewes that were fitted with instruments for long-term monitoring were randomized to receive a two-step intravenous infusion of levobupivacaine, bupivacaine, or ropivacaine, in a blinded manner, for 1 h. Maternal and fetal hemodynamics were monitored during the study. Arterial blood samples were drawn at 30 and 60 min of infusion from the mother and fetus to determine the acid-base status (60 min only) and serum drug concentrations. The fetal brain, heart, liver, lungs, adrenal glands, and kidneys were obtained to measure tissue drug levels. Maternal blood pressure, central venous and intraamniotic pressures, acid-base status and uterine blood flow were unaffected by any drug infusion. In contrast to the other two local anesthetics, the infusion of bupivacaine was associated with a small but significant decrease in the ewe's heart rate. At the end of the study, the heart rate in the bupivacaine-treated animals was significantly less than in the animals treated with the other two drugs. All fetuses were in good condition at the start of study, and none of the local anesthetics affected fetal well-being. No significant differences were found among the three drugs in the maternal serum, fetal serum, fetal tissue concentrations, and tissue:serum concentration ratios. Levobupivacaine was similar to bupivacaine and ropivacaine in causing no important hemodynamic changes in the pregnant ewe and fetus. There were no significant differences in the fetal serum and tissue levels of the drugs.

Fetal response to neutral gas and liquid media for intraamniotic distension

Purpose: This study was aimed at comparing the effects of a neutral liquid and a neutral gas used as intraamniotic media on umbilical blood flow, O 2 delivery, blood pressure, acid-base status, and electrolytes in the fetus at escalating intraamniotic pressures. Methods: Eight fetal lambs underwent invasive monitoring of common umbilical blood flow, blood pressure, blood gases, sodium, and hematocrit, as intraamniotic pressure was raised from 0 to 30 mm Hg. The animals were divided equally in two groups depending on the intraamniotic medium used (group I, warmed saline and group, II, air). Maternal systemic blood pressure, O 2 saturation, and temperature were kept constant. Results: In each group, a threshold level of intraamniotic pressure was evident, above which there was a significant decrease in the common umbilical artery blood flow, with concomitant fetal hypoxemia and hypercarbia. This intraamniotic pressure threshold was 20 mm Hg in group I (saline), but only 15 mm Hg in group II (air). Conclusions: Although both a neutral liquid and a neutral gas can safely be used as intraamniotic media, a neutral liquid medium allows for a wider range of safe intrauterine working pressure (0 to 20 mm Hg), as compared with a neutral gas (0–15 mm Hg).

Fetal carotid blood flow during videofetoscopy

Background/Purpose: Intracranial bleeding has been reported as one of the complications of both open and minimally invasive fetal surgery and putatively attributed to intraoperative fluctuations of carotid blood flow. The aim of this study was to look at fetal carotid blood flow and its relationship with umbilical blood flow, blood pressure, oxygen delivery, and acid-base status in the fetus at various intraamniotic pressures with both liquid and gas media during fetoscopic surgery. Methods: Six 115- to 130-day-gestation ewes underwent continuous invasive systemic blood pressure monitoring in the descending aorta. A hysterotomy was performed. A 6-mm ultrasonic blood flow probe was placed around the common umbilical artery at its origin from the fetal aorta. This was followed by placement of a double-lumen, 4F catheter in the fetal descending aorta through a femoral artery. A 4-mm ultrasonic blood flow probe was then placed around the fetal left common carotid artery. A pressuremonitoring, multiperforated catheter was placed inside the amniotic cavity. The fetus was repositioned inside the uterus, which was then closed. The abdominal wall was closed loosely. No further manipulation was performed for 1 hour. Intraamniotic pressure was raised from 0 to 30 mm Hg at 5-mm Hg intervals by infusing either warmed saline or medical air. Common umbilical artery and left carotid artery blood flows, blood pressure, blood gases, bicarbonate, sodium, and hematocrit were recorded in all fetuses at each 5-mm Hg interval. Maternal systemic blood pressure, O 2 saturation, and temperature were kept constant. Results: Carotid blood flow remained stable within the intraamniotic pressure range studied (0 to 30 mm Hg), despite the significant drop in common umbilical artery blood flow uniformly observed above 20 mm Hg when saline was infused and above 15 mm Hg when air was infused. There was fetal hypoxemia and hypercarbia concomitant with decreased common umbilical artery blood flow (however, without fetal acidosis, because of compensatory elevation of bicarbonate). Within the intraamniotic pressure range studied, fetal aortic blood pressure, sodium, and hematocrit did not vary significantly, even when there was decreased umbilical blood flow. Conclusions: Fetal carotid blood flow is protected, possibly autoregulated, remaining stable even after umbilical blood flow decreases as a consequence of elevated intrauterine pressures up to 30 mm Hg during videofetoscopy. These data suggests that perioperative intracranial bleeding related to videofetoscopic surgery is caused by factors other than fluctuations of cerebral blood flow.

Patterns of fetal perinasal fluid flow in cases of congenital diaphragmatic hernia

OBJECTIVE(S): Our purpose was to expand the previous reported series of observations of fetal perinasal fluid flow in cases of antenatally diagnosed congenital diaphragmatic hernia, characterize the timing parameters of the fetal breath cycle, and define the relationship of fetal perinasal fluid flow and the diaphragmatic component of fetal breathing movements. Our hypothesis was that characteristics of diaphragm-related and nondiaphragm-related perinasal fluid flow and other breath cycle characteristics differ in cases of congenital diaphragmatic hernia compared with controls. STUDY DESIGN: Fetal perinasal fluid flow velocity and fetal chest wall movements were studied in 24 cases of uncomplicated pregnancy, and flow was studied in 24 cases of antenatally diagnosed congenital diaphragmatic hernia at gestational ages ranging from 30 to 41 weeks. The examination of fetal perinasal fluid flow velocity was performed with use of an ultrasonography system applying color flow and spectral Doppler analysis. Breath-to-breath interval, time of inspiration, time of expiration, and peak inspiratory and expiratory velocities were determined for each type of perinasal flow. RESULTS: The study revealed that the time of expiration in cases of congenital diaphragmatic hernia at 30 to 36 and 37 to 41 weeks of gestation was significantly shorter than in cases of uncomplicated pregnancy. The ratio of time of inspiration and breath-to-breath interval in cases of diaphragmatic hernia was approximately 30% higher ( p = 0.001) at 30 to 36 weeks of gestation than in cases of uncomplicated pregnancy. The study also showed that in cases of congenital diaphragmatic hernia the expiratory peak velocity ratio at 30 to 36 weeks of gestation was significantly lower than in cases of uncomplicated pregnancy. CONCLUSIONS: We conclude that by Doppler ultrasonography measurements of fetal perinasal fluid flow, in cases of congenital diaphragmatic hernia, we can evaluate the timing parameters of fetal diaphragm-related breath cycles, the relationship of intraalveolar and intraamniotic pressures, and fetal upper respiratory tract resistance. Fetuses with diaphragmatic hernia spent significantly more time with diaphragm-nonrelated perinasal flow than did fetuses in cases of uncomplicated pregnancy, which can cause the increased loss of lung liquid and consequently be associated with pulmonary insufficiency in the early neonatal period. (Am J Obstet Gynecol 1997;176:807-13.)

Reducing the Deleterious Effects of Intrauterine CO2during Fetoscopic Surgery

The fetoscopic approach to fetal intervention is a promising minimally invasive technique for correcting congenital anomalies in utero. However, expansion of the amniotic cavity with CO2to visualize the fetus causes fetal hypercarbia and acidosis. We assessed whether maternal hyperventilation during intrauterine CO2insufflation could attenuate the fetal hypercarbic acidosis. Seven fetal lambs of 105 ± 2 days (mean ± SEM) gestation (term = 145 days) were instrumented with a carotid arterial catheter in utero. After 7 ± 1 days of recovery, fetoscopic exposure was obtained with intrauterine insufflation of CO2at 10 mmHg of intraamniotic pressure. After 30 min, the ewe was hyperventilated at a mean respiratory rate of 23/min for 30 min under continuous insufflation. The uterus was then deflated and following 1 hr of stabilization, and the same protocol of CO2pneumometrium was repeated. Fetal and maternal arterial blood was sampled at baseline and at 15 min intervals. FetalPaCO2increased during 30 min of CO2insufflation (50.8 ± 2.8 vs. 72.3 ± 5.0 mmHg,P< 0.01); however, this change was reversed (to 51.5 ± 3.0 mmHg,P< 0.01) by 30 min of maternal hyperventilation. The fetus developed acidosis after 30 min of CO2pneumometrium (pH 7.350 ± 0.012 vs. 7.236 ± 0.026,P< 0.01); this was also reversed (to 7.366 ± 0.019,P< 0.01) by maternal hyperventilation. These results were reproducible during the second CO2insufflation challenge. Fetal hypercarbic acidosis during fetoscopy with CO2insufflation is reduced by maternal hyperventilation.

Inhibition and augmentation of progesterone production during pregnancy: Effects on parturition in rhesus monkeys

OBJECTIVES: Uterine quiescence during mammalian pregnancy is attributed to progesterone. However. systemic progesterone levels remain elevated in primates before parturition. Epostane, a selective 3β-hydroxysteroid dehydrogenase inhibitor, and progesterone (with or without epostane) were administered to late pregnant rhesus monkeys to clarify the role of progesterone in primate parturition. STUDY DESIGN: On days 122 to 132 of gestation (term 167 days), 11 rhesus monkeys (Macaca mulatta) with timed pregnancies were divided into three treatment groups: (1) epostane alone (10 mg/kg subcutaneously), (2) epostane with progesterone subcutaneously in Silastic silicone rubber capsules, and (3) progesterone implants only with no surgical instrumentation. Maternal and fetal blood and amniotic fluid were sampled for progesterone, estrone, estradiol, cortisol, testosterone, androstenedione, dehydroepiandrosterone, dehydroepiandrosterone sulfate, and amniotic fluid was sampled for prostaglandins E 2 and F 2α. Uterine activity was monitored continuously by electromyography and intraamniotic pressure. Cervical status was assessed by a modified Bishop's score. Production of prostaglandins E 2 and F 2α by amnion was determined by tissue superfusion. The group of three noninstrumented monkeys, which received only progesterone Silastic silicone rubber implants subcutaneously at 146 to 148 days, were observed until spontaneous vaginal delivery. RESULTS: Epostane reduced maternal and fetal progesterone levels by 75% and 50%, respectively, followed by increased uterine activity and cervical ripening within 24 hours and vaginal delivery within 48 hours. Amniotic fluid progesterone decreased to undetectable levels. Progesterone implants prevented the epostane-induced decrease in maternal and fetal progesterone levels and the associated myometrial and cervical changes until the implants were removed. Alterations in other steroid hormones were consistent with inhibition of 3β-hydroxysteroid dehydrogenase. Amniotic prostaglandin E 2 production was increased sixfold by epostane ( p < 0.05) but did not reach the high levels normally seen at spontaneous parturition. Animals that received progesterone implants alone had markedly elevated circulating progesterone concentrations yet were delivered spontaneously at term (range 163 to 167 days). CONCLUSIONS: Progesterone withdrawal induces preterm labor and delivery (which can be blocked by progesterone substitution) but exogenous progesterone, even in substantial quantities, does not prevent parturition at term. (Am J Obstet Gynecol 1997;176:682-91.)

Intraabdominal carbon dioxide insufflation in the pregnant ewe. Uterine blood flow, intraamniotic pressure, and cardiopulmonary effects.

Laparoscopic surgical procedures are being performed in pregnant women with increasing frequency. Maternal-fetal physiologic changes occurring during intraabdominal carbon dioxide insufflation are poorly understood, and maternal-fetal safety is of concern during carbon dioxide pneumoperitoneum. A previous pilot study using end-tidal carbon dioxide-guided ventilation resulted in maternal and fetal acidosis and tachycardia during carbon dioxide pneumoperitoneum. Using serial arterial PCO2 to guide ventilation, this study was designed to evaluate maternal-fetal cardiopulmonary status, uterine blood flow, and the intraamniotic pressure effects of intraabdominal carbon dioxide insufflation in singleton pregnant ewes between 120 and 135 days of gestation. In a prospective randomized cross-over study, nine ewes were to receive either abdominal insufflation with carbon dioxide to an intraabdominal pressure of 15 mmHg (n = 9; insufflation group) or receive no insufflation (n = 9; control group). Anesthesia was induced with thiopental and maintained with end-tidal halothane (1 to 1.5 minimum alveolar concentration/100% oxygen). Mechanical ventilation was guided by serial maternal arterial blood gas analysis to maintain PaCO2 between 35 and 40 mmHg. Data from insufflated animals were collected during insufflation (60 min) and after desufflation (30 min). Control group data were collected and matched to similar time intervals for 90 min. Ewes were allowed to recover, and after a rest period (48 h) they were entered in the cross-over study. During insufflation there was a significant increase (P < 0.05) in maternal PaCO2 to end-tidal carbon dioxide gradient and minute ventilation, with concomitant decreases in maternal end-tidal carbon dioxide and PaO2. Intraamniotic pressure increased significantly during insufflation. No significant changes were observed in maternal hemodynamic variables, fetal variables, or in uterine blood flow during the study. There were no fetal deaths or preterm labor in any of the animals during the experiment. During the 1-h insufflation, a marked increase in PaCO2-to-end-tidal carbon dioxide gradient was observed, suggesting that capnography may be an inadequate guide to ventilation during carbon dioxide pneumoperitoneum in the pregnant patient. No other significant circulatory changes were observed.

Amniotic fluid pressure in twin-to-twin transfusion syndrome: an objective prognostic factor.

Severe twin-to-twin transfusion syndrome presenting before 28 weeks' gestation is associated with a high neonatal mortality and morbidity due to polyhydramnios-related very premature delivery or intrauterine death of one or both twins. Management options include serial amniodrainages or laser coagulation of the intertwin placental anastomoses; however, early antenatal prognostic factors are lacking. Serial amniocenteses were performed in 9 pregnancies with twin-to-twin transfusion syndrome presenting with second-trimester polyhydramnios, and serial measurements of amniotic fluid pressure were made. Although in 8 cases the pre-drainage pressure was above the 95th centile of the normal range for singleton pregnancies, the pressures were lower in the pregnancies resulting in two livebirths than in the cases where one or both babies died. This study suggests that patients presenting with intraamniotic pressure > 17 mm Hg cannot be safely managed by serial amniodrainages.