In the past, the long axis of the birth canal above and below the ischial spines was arbitrarily divided into thirds by some and into fifths (approximately 1 em) by other groups. In 1989, the American College of Obstetricians and Gynecologists adopted the classiication of station that divides the pelvis above and below the spines into ifths. Each ifth represents 1 em above or below the spines. hus, as the presenting fetal part descends from the inlet toward the ischial spines, the designation is -5, -4, -3, -2, -1i, then 0 station. Below the spines, as the presenting fetal part descends, it passes +1, +2, +3, +4, and +5 stations to delivery. Station + 5 em corresponds to the fetal head being visible at the introitus.
If the leading part of the fetal head is at 0 station or below, most often the fetal head has engaged-thus, the biparietal plane has passed through the pelvic inlet. f the head is unusualy moded or f caput succedaneum ormation is extensive, or both, engagement might not have taken place although the head appears to be at 0 station.
In a study done at five teaching centers in Denver, residents, nurses, and faculty were surveyed to determine what definitions were being used to describe fetal station (Carollo, 2004). Four diferent deinitions were in use. Disturbingly, these investigators found that few caregivers were aware that others were using diferent deinitions of station! Dupuis and associates (2005) tested the reliability of clinical estimations of station using the position of the leading part in centimeters above or below the spines. A birth simulator was used in which station could be precisely measured and compared with the vaginal examination done by clinicians. hey reported that the clinical examiners were incorrect a third of the time.
hese ive characteristics-cervical dilation, efacement, consistency, position, and fetal station-are assessed when tabulating the Bishop score. his score is commonly used to predict labor induction outcome and is discussed in Chapter 26 (p. 505). Taken together, these factors suggest the subjective "favorability" of the cervix for induction success.
When a woman is admitted in labor, most often the hematocrit or hemoglobin concentration is checked. he hematocrit can be measured easily and quickly. At Parkland Hospital, blood is collected in a standard collection tube with anticoagulant. From this, a heparinized capillary tube is filled to spin in a microhematocrit centrifuge in the labor and delivery unit. his provides a hematocrit value within 3 minutes. he initial collection tube is also sent to the hematology laboratory for evaluation if the point-of-care hematocrit is <30 volume percent. Another labeled tube of blood is allowed to clot and sent to the blood bank for blood type and antibody screen, if needed. A final sample is collected for syphilis and human immunodeficiency virus (HIV) serology. In some labor units, a cleancatch voided specimen is examined in all women for protein and glucose. At Parkland Hospital, however, we obtain a urine specimen for protein determination in hypertensive women only (Table 40-1, p. 712).
Women with no prenatal care are considered to be at risk for syphilis, hepatitis B, and HIV, and laboratory screening studies for these, as well as a blood type and antibody screen, are performed (American Academy of Pediatrics and American College of Obstetricians and Gynecologists, 2017). Some states, for example, Texas, require routine testing for syphilis, hepatitis B, and HIV in all women admitted to labor and delivery units, even if these were done during prenatal care.
• Management of First-Stage Labor