Indicators of Uterine Preparedness For Labor
Indicators of Uterine Preparedness For Labor
The threshold for the active phase of labor is suggested to reliably begin at a "cervical dilatation of 3 to 5 cm or more, in the presence of uterine contractions". However, investigators report that these criteria do not validly describe active labor onset for a large percentage of nulliparous women with spontaneous labor onset when traditional cervical dilation expectations are used to differentiate active from earlier labor. The clinical dilemma is that many women are inadvertently admitted prior to progressive labor (i.e., pre-active labor) yet held to dilation rate expectations of active labor. It is possible that women admitted early and given interventions aimed at accelerating labor progress (e.g., oxytocin augmentation) may be disadvantaged during labor in that such intervention may interrupt the time necessary for important physiological changes within the uterine and reproductive tissues to more fully manifest. This may, in part, explain why women admitted early in labor are more prone to oxytocin augmentation and are more than twice as likely to be delivered via cesarean.
Change in the activity of the enzyme lactate dehydrogenase (LDH) within uterine muscle during pregnancy and possibly throughout labor is a key physiological adaptation that may facilitate efficient uterine activity during labor. LDH is a predominantly intracellular, cytoplasmic enzyme that catalyzes the interconversion of pyruvate and lactate [Pyruvate+NADH+H ↔ (L)-lactate+NAD], a process essential for adenosine triphosphate (ATP) production. LDH is composed of two different types of polypeptide chains, commonly called 'H' and 'M,' which combine to form either homotetramer isoenzymes composed of all 'H' chains [LDH1 (H4)] or all 'M' chains [LDH5(M4)] or heterotetramer isoenzymes composed of a mixture of 'H' and 'M' chains [LDH2 (H3M1), LDH3 (H2M2), LDH4 (H1M3)]. The profile expression of LDH isoenzymes differs between body tissues depending on typical oxygen availability, e.g., more H-subunit dominant isoenzymes are available in tissues relying on aerobic metabolism, such as the heart, while M-subunit dominant isoenzymes are more abundant in tissues using anaerobic metabolism, such as skeletal muscle and liver. The isoenzyme profile is also capable of adaptation within body tissues in response to appropriate signals, thus ensuring the tissue consistently maintains adequate ATP production.
The majority of studies measuring LDH levels during pregnancy are from the late 1950s through the 1970s. In myometrial muscle, LDH isoenzymes shift toward a more anaerobic profile as pregnancy advances, speculatively, to better equip the uterus to contend with hypoxic episodes related to labor contractions. As a result, LDH3 and/or LDH4 have been reported to be in greatest concentrations in the pregnant myometrium at term. Anaerobic shifting is important because otherwise intermittent hypoxia and resultant acidosis would rapidly reduce contractile force. The pattern and timing of LDH isoenzyme profile shifting throughout late pregnancy and labor remains largely unknown.
LDH is released from its tissue of origin and enters the general circulation when cells are broken down or damaged. Because most tissues have LDH activities that are 500–700 times greater than that found in normal serum, a significant elevation of serum LDH occurs with even small amounts of tissue breakdown. While total serum measurement of LDH provides only a non-specific measure of cellular breakdown/damage, determining specific LDH isoenzyme patterns is useful in the differential diagnosis of certain pathologic states. This is possible because tissue breakdown releases the isoenzymes contained within that particular tissue, leading to a change in the serum profile measured systemically. Isoenzyme measures can assist in diagnosing pathologic processes such as myocardial infarction, liver disease, and pre-eclampsia.
During normal labor, levels of total myometrial LDH decline from levels present before labor with a disproportionate decrease in 'M' dominant chains over 'H' dominant chains. This finding aligns with reports that maternal serum total LDH concentrations are higher in the postpartum period than is normally found during the pre-labor period, peaking approximately 24–48 hours after delivery. Given the tremendous amount of work performed and stress endured by the uterus during labor coupled with rapid uterine involution following delivery, it is likely that serum LDH isoenzyme levels measured after labor, in otherwise healthy women, predominantly reflect the enzymatic profile within the uterine muscle that existed during the labor period. This has been suggested by other research teams. This means that LDH isoenzyme levels measured 24–30 hours after labor may serve as a retrospective indicator of uterine preparedness for labor.
The primary objective of this study was to describe relationships between maternal serum LDH isoenzymes measured 24–30 hours post-delivery and rates of cervical dilation during the first 4 hours following hospital admission for spontaneous labor onset. We also aimed to compare differences in post-delivery LDH profiles between women admitted to the hospital in pre-active versus established active labor. We hypothesized that better uterine preparedness for labor as evidenced by more efficient labor progression would be associated with a more anaerobic post-delivery serum LDH isoenzyme profile.
Background
The threshold for the active phase of labor is suggested to reliably begin at a "cervical dilatation of 3 to 5 cm or more, in the presence of uterine contractions". However, investigators report that these criteria do not validly describe active labor onset for a large percentage of nulliparous women with spontaneous labor onset when traditional cervical dilation expectations are used to differentiate active from earlier labor. The clinical dilemma is that many women are inadvertently admitted prior to progressive labor (i.e., pre-active labor) yet held to dilation rate expectations of active labor. It is possible that women admitted early and given interventions aimed at accelerating labor progress (e.g., oxytocin augmentation) may be disadvantaged during labor in that such intervention may interrupt the time necessary for important physiological changes within the uterine and reproductive tissues to more fully manifest. This may, in part, explain why women admitted early in labor are more prone to oxytocin augmentation and are more than twice as likely to be delivered via cesarean.
Change in the activity of the enzyme lactate dehydrogenase (LDH) within uterine muscle during pregnancy and possibly throughout labor is a key physiological adaptation that may facilitate efficient uterine activity during labor. LDH is a predominantly intracellular, cytoplasmic enzyme that catalyzes the interconversion of pyruvate and lactate [Pyruvate+NADH+H ↔ (L)-lactate+NAD], a process essential for adenosine triphosphate (ATP) production. LDH is composed of two different types of polypeptide chains, commonly called 'H' and 'M,' which combine to form either homotetramer isoenzymes composed of all 'H' chains [LDH1 (H4)] or all 'M' chains [LDH5(M4)] or heterotetramer isoenzymes composed of a mixture of 'H' and 'M' chains [LDH2 (H3M1), LDH3 (H2M2), LDH4 (H1M3)]. The profile expression of LDH isoenzymes differs between body tissues depending on typical oxygen availability, e.g., more H-subunit dominant isoenzymes are available in tissues relying on aerobic metabolism, such as the heart, while M-subunit dominant isoenzymes are more abundant in tissues using anaerobic metabolism, such as skeletal muscle and liver. The isoenzyme profile is also capable of adaptation within body tissues in response to appropriate signals, thus ensuring the tissue consistently maintains adequate ATP production.
The majority of studies measuring LDH levels during pregnancy are from the late 1950s through the 1970s. In myometrial muscle, LDH isoenzymes shift toward a more anaerobic profile as pregnancy advances, speculatively, to better equip the uterus to contend with hypoxic episodes related to labor contractions. As a result, LDH3 and/or LDH4 have been reported to be in greatest concentrations in the pregnant myometrium at term. Anaerobic shifting is important because otherwise intermittent hypoxia and resultant acidosis would rapidly reduce contractile force. The pattern and timing of LDH isoenzyme profile shifting throughout late pregnancy and labor remains largely unknown.
LDH is released from its tissue of origin and enters the general circulation when cells are broken down or damaged. Because most tissues have LDH activities that are 500–700 times greater than that found in normal serum, a significant elevation of serum LDH occurs with even small amounts of tissue breakdown. While total serum measurement of LDH provides only a non-specific measure of cellular breakdown/damage, determining specific LDH isoenzyme patterns is useful in the differential diagnosis of certain pathologic states. This is possible because tissue breakdown releases the isoenzymes contained within that particular tissue, leading to a change in the serum profile measured systemically. Isoenzyme measures can assist in diagnosing pathologic processes such as myocardial infarction, liver disease, and pre-eclampsia.
During normal labor, levels of total myometrial LDH decline from levels present before labor with a disproportionate decrease in 'M' dominant chains over 'H' dominant chains. This finding aligns with reports that maternal serum total LDH concentrations are higher in the postpartum period than is normally found during the pre-labor period, peaking approximately 24–48 hours after delivery. Given the tremendous amount of work performed and stress endured by the uterus during labor coupled with rapid uterine involution following delivery, it is likely that serum LDH isoenzyme levels measured after labor, in otherwise healthy women, predominantly reflect the enzymatic profile within the uterine muscle that existed during the labor period. This has been suggested by other research teams. This means that LDH isoenzyme levels measured 24–30 hours after labor may serve as a retrospective indicator of uterine preparedness for labor.
The primary objective of this study was to describe relationships between maternal serum LDH isoenzymes measured 24–30 hours post-delivery and rates of cervical dilation during the first 4 hours following hospital admission for spontaneous labor onset. We also aimed to compare differences in post-delivery LDH profiles between women admitted to the hospital in pre-active versus established active labor. We hypothesized that better uterine preparedness for labor as evidenced by more efficient labor progression would be associated with a more anaerobic post-delivery serum LDH isoenzyme profile.
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