A CST is positive if more than 50% of contractions are followed by a late slowdown. Uterine hyperstimulation, defined as contractions that occur more often than every 2 minutes or last more than 90 seconds, should not be present. Ambiguous CST occurs as part of hyperstimulation or with occasional late delays. A negative CST is a CST where no delays are detected. Uterine contraction agents and tocolytics are among the most commonly used drugs in obstetrics. The former are generally effective, but carry a risk of uterine hyperstimulation and fetal asphyxia in case of induction or increased birth. They should be carefully titrated and the condition of the fetus should be constantly monitored. Other indications include the initiation of an abortion and the prevention/treatment of postpartum bleeding. Tocolytics are only moderately effective and their use has not been clearly associated with improved neonatal outcomes. Therefore, funds with the highest safety profile should be provided when reviewing the use of these drugs. Uterine contractions during labor reduce uterine placental blood flow. Decreased blood flow during contractions is conversely associated with increased intrauterine pressure and contraction at the end of labor, diastolic velocities in maternal uteroplacental vessels disappear. Doppler ultrasound has been used to study changes in blood flow during labor in human pregnancies.
Several studies have confirmed that fetal blood flow during normal labor in an uncomplicated pregnancy usually remains intact, as the intransigent fetus can cope with intermittent decreased oxygen supply. Doppler velocimetry, performed between contractions, shows that the waveforms of blood velocities recorded by the umbilical artery and descending aorta, venous canal and middle cerebral arteries of the fetus do not change during labor. A finding of high levels of PI between contractions in the umbilical cord artery or in the venous canal is often associated with the further development of fetal asphyxia and surgical delivery with fetal load. However, the potential of Doppler studies in working as a clinical predictor of fetal asphyxia is still awaiting evidence. Medications used clinically during labor, such as tocolytics, opioids, or local anesthetics, can affect fetal and uteroplacental blood flow. Uterine contractions also occur during the monthly menstrual cycle and are recognized as menstrual cramps. Does the pelvis seem sufficient for the infant? A delay in the active phase indicates either insufficient effort of uterine contraction to enlarge the cervix, or mechanical obstruction of childbirth. Obviously, this is a critical issue, because therapeutic alternatives are very different. If the pelvis is clinically small and/or the fetus is large and the labor appears severe (for example. B, intense uterine contractions that occur every 2 minutes), the choice is for caesarean sections. If the fetoplastic relationship is favorable for vaginal delivery and contractions are rare, the choice is intravenous oxytocin, amniotomy or both. In the vast majority of cases, however, the obstetrician does not know if an increase in oxytocin will lead to a successful vaginal delivery or if a caesarean section will ultimately be necessary despite the increase in oxytocin.
Given the uncertainty as to whether mechanical obstruction or insufficient uterine activity is the problem, the right choice is usually to administer oxytocin to correct the latter, a decision that recognizes that if the former is present, the attempt will eventually fail. The data support longer periods of increased oxytocin for the non-progressive active phase of labour (at least 4 to 6 hours), provided that the FHR scheme is reassuring.29 All attempts should be made to correct any underlying maternal disease that could contribute to positive CST.10 For example, correcting severe maternal dehydration with strong intravenous hydration can lead to uterine hyperfusion and CST. abnormal. That`s right. Although myometric contractions move the fetus to the lower uterine segment, childbirth can only take place if the cervix — a cylindrical extension of the lower uterine segment that has a central canal that connects the uterus to the upper end of the vagina — expands. For most of pregnancy, the cylindrical wall of the cervix consists of a dense and rigid fibrous ECM, which is inflexible and maintains a narrow channel that resists the tensile forces generated by myometric contractions and increased intrauterine pressure. In the non-pregnant state, the cervical canal, although narrow, is opened to allow menstrual flow and sperm penetration. However, during pregnancy, the canal is closed by a mucus plug that separates the uterine and vaginal cavities. The mucus plug is usually evacuated late in pregnancy when the cervical canal expands. Uterine contractions at a rate of three in 10 minutes should occur with a low-dose (0.5 mU/min) oxytocin infusion or as a result of nipple stimulation.
The patient should remain in a semi-Fowler position for both techniques aimed at preventing aortocal compression and maternal hypotension. Both techniques for achieving uterine contractions have comparable efficacy, with CST nipple stimulation being more cost-effective.9 Myometric activity is strictly regulated during pregnancy. During the first and medium trimesters, myometrium tension is required to absorb fetal growth. When fetal growth is almost complete in late pregnancy, uterine activity is first stabilized, and then begins to increase in preparation for childbirth. We showed a link between uterine stretching, MMP expression and uterine relaxation during pregnancy. We also showed the role of sex hormones in promoting the effects of uterine stretching on MMP expression and uterine relaxation. MMP-1, MMP-2, MMP-3, MMP-7 and MMP-9 are found in amniotic fluid and fetal membranes during normal pregnancy. MMP-2 and MMP-3 are expressed constitutively, while MMP-9 is barely detectable until birth. At work, MMP-9 is the most important MMP responsible for gelatinolytic activity in membranes, while MMP-2 is dominant in decidua. These findings may have clinical relevance, as disrupting the balance of MMP or TIMPs could disrupt uterine activity and lead to preterm labor. MMP/TIMP imbalance can be further exacerbated by changes in sex hormone levels or their uterine receptors. Contractions can occur at any point in the uterine wall.
They are generally considered to be rounded « masses » that arch in the fruit space without altering the outer contour of the uterus (Fig. 20-22A). If it is located under the placenta, a contraction can cause the placenta to bend into the fruit space (Fig. 20-23A). If a contraction occurs in the lower uterine segment or cervix and there is a poorly positioned placenta, the placenta may appear mistakenly above the cervix with a misdiagnosis of placenta previa (Fig. 20-24). The structural basis of contractions is the relative movement of thick and thin filaments in the contractile apparatus, which allows them to gradually slide on top of each other during a contraction with a gradual shortening of the myocytes (called brachystases). Although this movement is similar in all muscles, several structural and regulatory features are unique to smooth muscles, including myometrium.186,187 In smooth muscles, the sarcarmic arrangement of thick and thin filaments seen in striped muscles is present on a much smaller scale, and the intermediate filaments of the cytoskeletal network maintain the structural integrity of these minisarcomers. Thin filaments fit into dense bands connected by the cytoskeletal network to generate force in any direction of the cell, creating greater force (greater shortening) than in striated muscle cells with relatively lower energy consumption. .