Coupling of uterine contractions during labor: a pilot study

A review of 2167 cardiotocograms revealed 53 (2.5%) with coupling of contractions. The data of these patients was compared to the data of 53 patients with cardiotocograms without coupling. In the coupling group there were more primigravidas (45 vs. 18), and a lower incidence of normal vaginal deliveries (11.3% vs. 83.0%). Vacuum and forceps deliveries occurred in 49.1% in the coupling group and cesarean births in 39.6%. The corresponding figures in the control group were 9.4% and 7.5%, respectively. Coupling seems to be a sign of dysfunctional labor associated with a high incidence of abnormal deliveries, but several confounding variables could not be ruled out.     

Changes in uterine blood flow during uterine contractions

During spontaneous and oxytocin-induced labor, recordings were made of relative uterine blood flow (thermistor method), intrauterine pressure, femoral venous and arterial pressures, and maternal heart rate. In prelabor, uterine blood flow exhibits frequent irregular waves quite independent of the observed uterine activity. During labor there is a characteristic relationship between uterine blood flow and uterine contractions. An initial decline in uterine blood flow precedes the contraction by about half a minute, followed by partial or complete recovery in the early contractile phase. A second drop begins as the intrauterine pressure reaches about 30 mm. Hg, and the decline continues to the peak of the contraction or beyond. After the contraction is completed, the uterine blood flow recovers to its original level.     

Changes in fetal supraventricular extrasystoles during uterine contractions in labour.

The electrocardiogram and phonocardiogram were recorded from a fetus exhibiting supraventricular ectopic beats during labour. The ectopic beats showed increased amplitude of the first heart sound (S1) compared to sinus and postectopic beats; the R-S1 interval was prolonged and the mechanical systole, measured as the S1-S2 interval, shortened. During uterine contractions these parameters were measured every 10 sec. The S1 amplitude of the ectopic beats decreased; simultaneously the R-S1 interval increased and the S1-S2 interval shortened. The changes were delayed compared to the amniotic pressure curve. The changes found can be explained by a shift of blood between the fetus and placenta, caused by uterine contraction.     

Effect of exercise during pregnancy on uterine contractions

External tocometry was performed one hour before and one hour after pregnancy gymnastics in 102 healthy pregnant women between 25th and 38th gestational week. There were no statistically significant differences in the number of contractions. The short-term increase in frequency of contraction was without any clinical importance. No prolongation of the duration of contractions could be observed with advanced pregnancy. 34 per cent of the women were delivered in the 41st gestational week, 32 per cent before the 40th one. In case of threatening premature delivery gymnastics are contraindicated with exclusion of relaxation exercises. They are allowed only in case that a good attitude of contractions before and after gymnastics can be demonstrated by objective external tocometry.     

Effect of an oxytocin antagonist on plasma oxytocin levels during nocturnal uterine contractions in the pregnant baboon.

TT-235 is a potent oxytocin (OT) antagonist that blocks the action of OT at the receptor level. Previous studies have shown that pregnant baboons demonstrate nocturnal uterine contractions induced by OT as they near delivery. The purpose of this study was to evaluate the changes in plasma OT levels following uterine contraction blockage with TT-235. A tethered pregnant baboon model in its last trimester of pregnancy was used. Three blocks of arterial blood samples, immediately before, plus 1 h and plus 2 h following an OT antagonist injection, were collected once nocturnal uterine contractions were detected. Each block consisted of a continuous 10 min withdrawal with 10 samples per block (1 ml/min). A TT-235 dosage of 300 micrograms/kg and saline for control were utilized. Uterine activities were monitored as pressure changes in the amniotic fluid, and the frequency and mean amplitude of contractile activity per 10 min intervals were expressed as contractile force. Plasma OCT levels were determined by a radioimmunoassay following plasma extraction with petroleum ether. The contractile force was decreased by 77% (p < 0.05) within 2 h after TT-235 administration while it increased 23% following saline infusion. Plasma OT levels were unchanged following saline infusion while they increased 82% (p < 0.05) 2 h after the administration of TT-235. If a positive feedback existed between uterine contractions and OT release, one would expect plasma OT levels to be decreased with contractile activity following TT-235 infusion. Since this is not the case in the present study, the data suggest that there is either a negative feedback or an independent relationship between nocturnal uterine contractions and OT release.     

Fetal cardiorespiratory changes during spontaneous prelabor uterine contractions in sheep

Fetal cardiorespiratory changes during spontaneous prelabor uterine contractions (called contractures) were studied in 12 chronically catheterized fetal sheep at 120 to 143 days' gestation. During contractures the carcass blood flow increased significantly from 27 +/- 2 (SEM) to 32 +/- 3 ml/min/100 gm. There were no significant changes in combined ventricular output or in blood flow to the umbilical circulation, brain, heart, adrenal glands, gut, kidney, and lung. Fetal arterial blood pressure increased from 57 +/- 2 to 62 +/- 1 mm Hg (p less than 0.001) during contractions. There were no significant changes in fetal heart rate. In the fetal femoral artery during contractures the oxygen content decreased from 6.1 +/- 0.2 to 5.4 +/- 0.2 ml/dl of blood (p less than 0.001), and carbon dioxide tension increased significantly from 44 +/- 0.4 to 45 +/- 0.4 mm Hg (p less than 0.001). The pH did not change. The increase in carcass blood flow during contractures suggests that there was an increase in fetal skeletal muscular activity or tone. An increase in fetal skeletal muscle activity, together with a decrease in uterine blood flow could explain the small decrease in fetal oxygen content that occurs with each contracture. Fetal compression and/or changes from rapid eye movement to synchronized sleep or arousal observed during contractures are possible stimuli causing increased fetal skeletal muscle tone or activity. Since contractures periodically result in neuromuscular activity in the fetus in its protected fluid-filled environment, they may play a key role in fetal neuromuscular development by stimulating "exercising" in the fetus in utero.     

Increased beat-to-beat variability during uterine contractions: A common association in uncomplicated labor

A computerized system was used during labor to provide a quantitative and objective analysis of fetal heart rate, beat-to-beat variability, and uterine contractions. Twenty-nine healthy pregnant women at term participated in this study. Each woman was studied for a 40-minute period during the active phase of spontaneous labor. The results indicate that beat-to-beat variability rises from a value of 4.62 ± 1.11 (mean ± SD) between contractions to 6.86 ± 1.53 during contractions. This rise is significant (p < 0.01). At the same time, changes in fetal heart rate are small, inconsistent, and not significant. We conclude that an increased beat-to-beat variability is commonly associated with uterine contractions in normal fetuses. This increase is probably due to mild hypoxia caused by decreased perfusion of the placenta and to increased vagal tone caused by fetal head compression.     

Effect of heat on uterine contractions during normal labor

The effect of local application of heat on the abdominal wall on uterine activity was evaluated in 15 full-term multiparous women early in the first stage of labor. Cardiotocographic monitoring showed that heat induces a significant increase in uterine activity without causing any abnormal fetal heart changes. The stimulated contractions return back to base line level following removal of heat. The application of heat on the abdominal wall of women in early labor appears to offer a new non-pharmacological modality for the stimulation of uterine activity.     

The effect of disopyramide on uterine contractions during pregnancy

To evaluate the effect of disopyramide on uterine contractions during pregnancy, the drug was given for 48 hours to 10 women with indications for labor induction. Placebo was given to 10 other women with the same indications for induction. During the study period, regular uterine contractions occurred in 10 women in the study group, as compared with none in the control group (p less than 0.0001). Eight women in the study group were delivered of infants within 48 hours, as compared with none in the control group (p less than 0.0001). The mean time until the appearance of regular uterine contractions in the study group (4.15 +/- 1.76 hours) was significantly shorter (p less than 0.001) than that in the control group (56.13 +/- 5.28 hours). Patients who were not delivered of infants within 48 hours received other medications (prostaglandin E2, oxytocin). The mean maternal blood level of disopyramide at the time of appearance of uterine contractions was 1.52 +/- 0.9 mg/ml. The mean maternal level at delivery was 0.93 +/- 0.43 mg/ml and the cord blood level at the time of delivery was 0.33 mg/ml (cord blood/maternal level ratio = 0.36, r = 0.73, p less than 0.05). These results indicate that disopyramide should not be used in pregnancy for antiarrhythmic purposes because it may induce uterine contractions and delivery.     

Inhibition of uterine contractions of premature labour with an oxytocin analogue. Results from a pilot study

A competitive inhibitor of the action of oxytocin on the uterus, 1-deamino-2-D-Tyr-(OEt)-4-Thr-8-Orn-oxytocin, was studied for the first time in 13 patients with established, uncomplicated premature labour. Intravenous infusion of 10-100 micrograms/min of the analogue was given for 1-10 h and the effect was monitored by external cardiotocography. In all women an inhibition of uterine activity was observed, and in the majority of patients infused with 25 micrograms/min and a total dose of about 5 mg or more of the drug total inhibition of uterine contractions was achieved. There were no effects on the maternal and fetal pulse rates, nor were there any other side-effects. The results of this preliminary study support the concept of an increased concentration of uterine oxytocin receptors being aetiologically important in uncomplicated premature labour. They also suggest that the present oxytocin antagonist could be an interesting therapeutic alternative in the condition, primarily because of the marked selectivity of its effect.     

Inhibition of uterine contractions of premature labour with an oxytocin analogue. Results from a pilot study

Summary. A competitive inhibitor of the action of oxytocin on the uterus, l-deamino-2-D-Tyr-(OEt)-4-Thr-8-Orn-oxytocin, was studied for the first time in 13 patients with established, uncomplicated premature labour. Intravenous infusion of 10–100 μg/min of the analogue was given for 1–10 h and the effect was monitored by external cardiotoco-graphy. In all women an inhibition of uterine activity was observed, and in the majority of patients infused with 25 μg/min and a total dose of about 5 mg or more of the drug total inhibition of uterine contractions was achieved. There were no effects on the maternal and fetal pulse rates, nor were there any other side-effects. The results of this preliminary study support the concept of an increased concentration of uterine oxytocin receptors being aetiologically important in uncomplicated premature labour. They also suggest that the present oxytocin antagonist could be an interesting therapeutic alternative in the condition, primarily because of the marked selectivity of its effect.     

Doppler velocimetry measured in retrochorionic space and uterine arteries during early human pregnancy

The natural course of uterochorionic vascular resistance during the first trimester of pregnancy is described. We performed a weekly study using a pulsed Doppler in 25 normal pregnancies, with a total of 191 examinations made. The flow velocity waveform was studied simultaneously in the retrochorionic area as well as in the uterine arteries. Different velocimetry indices were analysed, which demonstrated the feasibility of the (D/S) x 100 index for study of the retrochorionic vessels and of the Pourcelot index (S-D/S) for the uterine arteries. A gradual weekly decrease in flow resistance was found, with significant differences before [(D/S) x 100 = 52.01 +/- 8.33; S-D/S = 0.83 +/- 0.09] vs after the 9th week [(D/S) x 100 = 58.9 +/- 8.78; S-D/S = 0.72 +/- 0.10]. Further evaluation of its predictive and diagnostic value in gestational pathology is necessary.     

Pressure-velocity analysis of uterine muscle during spontaneous dysmenorrheic contractions in vivo

Three-dimensional pressure-velocity (slope) topograms may be constructed to evaluate the uterine muscle's ability to contract under varying conditions of pressure load in vivo. This type of analysis indicates that even at intrauterine pressures that greatly exceed perfusion pressure, the uterus is capable of rates of change as high as +/- 120 mm Hg/sec. The topograms of dysmenorrheic women appear similar among women and from month to month. Dramatic differences in the topograms are noted before the development of menstrual pain and after nonsteroidal antiinflammatory drug therapy. This suggests a possible causal relationship to the pain of dysmenorrhea. These topograms may also represent a sensitive measure of physiology and therapeutic effects.