Head-to-cervix forces and their relationship to the outcome of labor

Article Abstract:

Since a major reason for performing cesarean section is the failure of labor to progress normally, reduction of the cesarean rate relies, in part, on better understanding and control of the physiology of labor. In particular, much remains to be learned about the role of pressure exerted by the fetal head on the cervix in influencing cervical dilatation. Researchers have differed in their interpretations of how pressure changes affect dilatation, but part of the confusion may stem from measuring pressure exerted by the head, rather than force. In this regard, force means the summation of all local or point forces (such as intrauterine pressure) acting to push the fetus out of the uterus. The head-to-cervix force was measured in 31 women by 4 transducers placed at the cervical opening and 3 on the fetal head. The construction of the transducers is explained. Women were monitored from the stage when the cervix was three centimeters dilated, and received oxytocin (a hormone that stimulates uterine contractions) if labor did not progress satisfactorily. Results from the analysis of approximately 2,010 contractions revealed that the correlation between active force and active pressure was 0.29. No differences were found between the subjects who delivered vaginally and those who delivered by cesarean section in the 50th percentile (the point below and above which scores of half the subjects fell) for active pressure or birth weight. However, the cervical dilatation rate was higher in the vaginal group, as was the 50th percentile of active force. The results indicate that adequate uterine contractions can occur with low head-to-cervix forces, and imply that agents used to enhance uterine contractions (such as oxytocin) are therefore not optimal. Measurement of head-to-cervix force may be a useful obstetrical tool. (Consumer Summary produced by Reliance Medical Information, Inc.)

Cervix uteri, Patient monitoring, Physiologic monitoring, Incompetent cervix

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Labor patterns in women with previous cesareans

Article Abstract:

A trial of labor and vaginal delivery are now commonly offered to selected women who have had a previous cesarean section. Although vaginal birth after cesarean (VBAC) is considered safe, the significance of abnormal occurrences during a trial of labor (whereby labor is allowed to continue long enough to determine whether delivery will be normal) is not clear. The characteristic patterns of labor were studied in 68 VBAC candidates and equal numbers of women without a history of cesarean delivery and who were delivering for the first time. Labor characteristics in the latent phase, first stage, and second stage of labor, as well as the rates of cervical dilation and descent (movement of the fetus in centimeters per hour) were evaluated. The labor characteristics of the women without a previous vaginal delivery were similar to those of women delivering for the first time. The labor characteristics of women with a previous cesarean section differed from the women delivering for the first time and those who had had a previous vaginal delivery. Women with a previous cesarean delivery experienced more labor disorders (41.9 percent) than women delivering for the first time (27.1 percent), those with both a previous cesarean history and vaginal birth history (14.3 percent), and those having multiple vaginal births (15.8 percent). Therefore, women who have had a previous cesarean delivery should have labor judged as though it were a first-time delivery. VBAC candidates who have had both vaginal and cesarean deliveries should have labor evaluated by the same criteria that are used for women having previous vaginal deliveries. (Consumer Summary produced by Reliance Medical Information, Inc.)

Evaluation, Childbirth, Delivery (Childbirth), Cesarean section

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A comparison of the ability of a sonographically measured biparietal diameter and the last menstrual period to predict the spontaneous onset of labor

Article Abstract:

The delivery date (estimated date of confinement, EDC) for pregnant women can be predicted in two different ways. One method computes the gestational age based on the date of onset of the mother's last menstrual period (LMP) before becoming pregnant; the other measures the biparietal diameter (BPD, the distance between two bones in the skull) of the fetal skull using ultrasound. The accuracy of the two EDC prediction methods was compared in 2,320 women who gave birth after the spontaneous onset of labor. Results showed that more than 85 percent of the women delivered within fourteen days of the EDC as predicted by both methods. For women whose fetuses underwent BPD determination, the EDC estimated in this manner was within seven days of the LMP estimate in 80 percent of the cases (1,858 women). The BPD estimate of delivery date was more accurate (closer to the actual day of delivery) for 264 cases, while the LMP prediction was better for 125. The women studied had optimal menstrual histories, with regular periods and a normal amount of bleeding. However, EDC estimates made by BPD and LMP differed by more than one week for one woman out of every five. In summary, BPD is the method of choice in cases where the two estimates differ by more than one week. The method is, of course, essential for women who do not know the date of their last menstrual period. (Consumer Summary produced by Reliance Medical Information, Inc.)

Usage, Measurement, Testing, Gestational age, Prenatal ultrasonography, Ultrasonics in obstetrics

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