VBAC Revisited Again
VBAC Revisited Again
Abstract & Commentary
Synopsis: Postpartum fever after cesarean delivery is associated with an increased risk of uterine rupture during a subsequent trial of labor.
Source: Shipp TD, et al. Obstet Gynecol. 2003;101: 136-139.
Vaginal birth after cesarean (VBAC) continues to be a hot topic, and in the most recent issue of Obstetrics & Gynecology, Shipp and colleagues attempted to determine which intrapartum or postpartum events correlated with uterine rupture in a subsequent pregnancy.
Shipp et al searched their database to find patients with uterine rupture (for a 12-year period) who had previously delivered in the same institution. Each of the 21 cases found were then matched carefully with 4 control VBAC cases that delivered initially by cesarean section over the same time period (without uterine rupture).
The only variable that emerged as being significantly related to uterine rupture was postpartum fever (> 38° C). Specifically, 8/21 (38%) of the uterine rupture group had a postpartum fever in their prior cesarean, compared with 13/84 (15%) in the control group (P = 0.03).
Comment by John C. Hobbins, MD
As mentioned in previous OB/GYN Clinical Alerts, the rate of cesarean section has risen to about 25% in the United States because of medico-legal, convenience, and other reasons, and there is every indication that this trend will head further skyward. Although some have taken a "who cares?" attitude to the point of making a case for cesareans on demand, there are plenty of data to indicate they are more costly and far from innocuous. Data aside, birth represents one of life’s most natural processes. However, 1 in 4 of these is now accomplished by a major surgical operation. What’s wrong with this picture?
This article suggests that patients with postpartum fever have a higher rate of later rupture during VBAC than those without this complication. The obvious take-home message is that postpartum fever is an indirect indicator of an infection that may adversely affect the quality of the scar, ultimately being tested during labor in the next pregnancy. Since the overwhelming majority of patients with postpartum fever will not have later uterine rupture, Shipp et al’s finding should in no way be a contraindication to VBAC. On the other hand, the absence of intra-uterine infection could drop the risk of VBAC in those wishing to undertake this option.
Parenthetically, although the numbers of patients in the study were small, Shipp et al found no relationship between rupture and 1) single or double layer closure of the uterine incision; 2) the use of antibiotics (75% of both ruptures and controls got them); and 3) white blood cell count (WBC).
From this and other studies, it seems that the most critical variable in uterine rupture is the strength of the scar, and, to date, the literature has provided few clues as to how to assess this. Until something else comes along, perhaps the best way to indirectly evaluate the potential for uterine rupture is through ultrasound assessment of wall thickness in the vicinity of the uterine scar. In a previous issue, this topic was tangentially covered. In 2 papers from Japan involving small numbers of patients, there appeared to be a relationship between wall thickness and uterine rupture. However, I overlooked a paper published in 1996 in the Lancet by a group of French investigators that provided much stronger evidence of the efficacy of using wall thickness to roughly determine risk of rupture for a given patient.1
The group evaluated 642 patients about to undergo VBAC at term with transabdominal ultrasound assessment of uterine wall thickness just under the bladder reflexion. The uterine rupture rate was 2.5%, and the rate of dehiscence was 1.5%. If the smallest thickness was 1.6-2.5 mm, the defect rate was 16%. If that diameter was greater than 4 mm, there were no uterine defects and if one used a cutoff of 3.5 mm, the negative predictive value was 99.3%.
The major argument against VBAC is its potential for increased neonatal and maternal morbidity. This is directly related to uterine rupture so if we had a very good idea of which patients were at very low risk of this through historical information (fever postpartum), scar strength (uterine wall thickness), and other variables such as cervical ripeness (another story), it should be possible to identify the majority of patients who could sail through labor as if they did not have a scar.
I promise this will be the last time for a while that this topic will be covered.
Dr. Hobbins is Professor and Chief of Obstetrics at the University of Colorado Health Sciences Center in Denver.
Reference
1. Rozenberg P, et al. Lancet. 1996;347:281-284.
Synopsis: Postpartum fever after cesarean delivery is associated with an increased risk of uterine rupture during a subsequent trial of labor.
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