A patient presents in labor at term. Clinical pelvimetry is performed. She has an oval-shaped pelvis with the anteroposterior (AP) diameter at the pelvic inlet greater than the transverse diameter. The baby is occiput posterior.
The patient most likely has what kind of pelvis?
By tradition, pelves are classified as belonging to one of four major groups, based on the shape of the pelvis. A line drawn through the greatest diameter of the pelvic inlet divides the pelvis into anterior and posterior sections, and the shape of these segments helps determine the pelvis type. The gynecoid pelvis is the classic female pelvis, with a posterior sagittal diameter of the inlet only slightly shorter than the anterior sagittal diameter. The posterior pelvis is rounded and wide, the sidewalls are straight, the spines are not prominent, and the pubic arch is wide. In the android pelvis, the posterior sagittal diameter at the inlet is much shorter than the anterior sagittal diameter, limiting the use of the posterior space by the fetal head. The sidewalls are convergent, the spines are prominent, and the pubic arch is narrowed. In the anthropoid pelvis, the AP diameter of the inlet is greater than the transverse diameter, resulting in an oval with large sacrosciatic notches, convergent side walls, prominent ischial spines, and a narrow pubic arch. The platypelloid pelvis is flattened with a short AP and wide transverse diameter. Wide sacrosciatic notches are common. The pelves of most women do not fall into a pure type and are blends of one or more of these types.
Pelvic examination is performed in a 34-year-old P0101 at 34 weeks’ gestation who is in labor. The patient is noted to be 6 cm dilated, and completely effaced with the fetal nose and mouth palpable. The chin is pointing toward the maternal left hip.
This is an example of which of the following?
The lie of the fetus refers to the relation of the long axis of the fetus to that of the mother, and is classified as longitudinal, transverse, or oblique. The presentation, or presenting part, refers to the portion of the baby that is foremost in the birth canal. The presentation may be cephalic, breech, or shoulder. Cephalic presentations are further classified as vertex, brow, or face. The position is the relative relationship of the presenting part of the fetus to the mother. In this instance, the fetus is cephalic, with the face presenting. In a face presentation, the fetal head is hyperextended so that the occiput is in contact with the fetal back, and the chin (mentum) is presenting. The mentum is the point of reference of the fetus when describing the position of the face. Since the mentum is pointing toward the mother’s left hip, the fetal position is described as mentum transverse. In vertex presentations, the occiput is the point of reference for determining position. In breech presentations, the sacrum is the point of reference.
You are counseling a 36-year-old obese, Hispanic G2P1 at 36 weeks’ gestation about route of delivery. During her first pregnancy, she was induced at 41 weeks’ gestation for mild preeclampsia, and delivered by cesarean as a result of fetal distress during her induction. The patient would like to know if she can have a trial of labor after cesarean (TOLAC) with this pregnancy.
Which of the following is the best response to this patient?
A patient with a prior low transverse incision may attempt a TOLAC. Repeat cesarean and TOLAC both have inherent risks. The main risk of TOLAC that increases maternal and neonatal morbidity is uterine rupture, the risk of which is impacted significantly by the location of the uterine incision. A low transverse incision is made transversely through the lower uterine segment, which does not actively contract during labor. The risk of uterine rupture after prior low transverse incision is less than 1%. The skin incision does not reflect the location of the uterine incision, and therefore is not an indicator of the suitability of TOLAC for a patient. Although a prior vaginal delivery increases the success rate for a successful VBAC, a prior vaginal birth is not a prerequisite for a TOLAC. If the patient desires a repeat cesarean delivery, this should be performed at 39 weeks as a scheduled procedure.
The patient wants to know about the probability of success if she chooses to undergo TOLAC.
What can you tell her about factors that impact the probability of success in TOLAC?
Good candidates for TOLAC are women in whom the balance of risks and benefits are acceptable to the patient and health care provider. Decisions regarding TOLAC must be made on an individual basis while taking these factors into account. Most evidence suggests that most women with one prior low transverse cesarean should be counseled about vaginal birth after cesarean (VBAC) and offered TOLAC. Factors that increase the probability of success include prior vaginal delivery and spontaneous labor. Factors that predict a decreased probability of success include increased maternal age, Hispanic or African American ethnicity, postdates gestation, and maternal obesity. Therefore, spontaneous labor prior to 40 weeks would provide this patient with the greatest chance of successful TOLAC.
The patient has still not gone into spontaneous labor at 41 weeks’ gestation. You see her in clinic and her blood pressure is 150/90 mmHg and she has +3 proteinuria on urine dipstick. You send her to labor and delivery for further evaluation, and her blood pressure remains elevated, consistent with a diagnosis of preeclampsia. You examine her cervix and find that it is closed and thick. She asks whether she can undergo induction of labor at this point.
What should you tell her about induction of labor?
Induction of labor for maternal or fetal indications is an option for women undergoing TOLAC. However, the chance of successful TOLAC with induction versus spontaneous labor is lower, and her unfavorable cervical examination decreases the potential success rate. Data support use of mechanical ripening agents, such as transcervical catheter, in this setting of an unfavorable cervix. Prostaglandins are not used for cervical ripening due to concerns over increased risk of uterine rupture.
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