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ORIGINAL RESEARCH |
From the Division of Maternal-Fetal Medicine, Department of Obstetrics and Gynecology and the Center for Clinical Epidemiology and Biostatistics, University of Pennsylvania Health System, Philadelphia, Pennsylvania.
Address reprint requests to: David M. Stamilio, MD, University of Pennsylvania Health System, 2000 Courtyard Building, 3400 Spruce Street, Philadelphia, PA 19104, E-mail: dstamili{at}cceb.med.upenn.edu
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Abstract |
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Methods: We used decision analysis to compare three strategies to select delivery method in women with autoimmune thrombocytopenia, funipuncture at term, intrapartum fetal scalp platelet sampling with delivery mode decisions based on platelet count in the first two strategies, and no testing of fetal platelets with delivery mode determined by standard obstetric criteria. We assumed that the goal of each strategy was to minimize the number of severely thrombocytopenic neonates delivered vaginally while maintaining an acceptable cesarean rate. Severe thrombocytopenia was defined as under 50,000 platelets per µL. Probabilities with ranges (used in sensitivity analyses) were derived from the medical literature.
Results: Of the two testing strategies, funipuncture was clearly preferable. Funipuncture resulted in zero cases of severely thrombocytopenic neonates delivered vaginally (as did scalp sampling), with a lower overall cesarean rate compared with fetal scalp sampling (36.6% versus 69.1%). Compared with the no-testing strategy, the funipuncture strategy reduced the number of severely thrombocytopenic neonates delivered vaginally (0 versus 82 per 1000) with a modest increase in the cesarean rate (1.9 cesareans to prevent vaginal delivery of one severely thrombocytopenic neonate).
Conclusion: Fetal scalp sampling should be abandoned in favor of funipuncture when testing for thrombocytopenia.
Autoimmune thrombocytopenia, also known as immune thrombocytopenic purpura (ITP), is an autoimmune disorder in which platelet destruction by the reticuloendothelial system is caused by an antiplatelet antibody. The incidence of ITP during pregnancy is roughly 1 to 2 per 1000 deliveries.1–3 Pregnancies affected by maternal ITP commonly are complicated by neonatal thrombocytopenia, and approximately 12% of neonates are severely thrombocytopenic at delivery.1,2,4–9 Thrombocytopenic neonates were reported to suffer intracranial hemorrhage resulting in long-term neurologic deficits.9–11 Those reports prompted some to recommend cesarean deliveries for all pregnant women with ITP, to avoid fetal passage through the bony pelvis and decrease the risk of intracranial hemorrhage.1 However, neither a causal relationship between vaginal delivery and intracranial hemorrhage, nor a protective effect of cesarean delivery has been proved or disproved,4,5 which is not surprising because studies that evaluated delivery mode were underpowered for evaluating a relatively rare outcome such as intracranial hemorrhage in a term neonate. Regardless, many physicians adhere to that biologically plausible presumption and recommend fetal-platelet counts in term gestations (by funipuncture or fetal scalp sampling) to detect severe fetal thrombocytopenia and to guide choice of delivery method. Most proponents of term fetal platelet sampling recommend cesarean deliveries for all infants with a fetal platelet count less than 50,000/µL.6,12–18 That strategy has been adopted clinically, without scientific proof for or against it, based on potential life-long, catastrophic outcomes of intracranial hemorrhage and on the perception of relatively less severe consequences of fetal-platelet testing at term. Other authors maintain that the risks of intracranial hemorrhage and other neonatal bleeding events in pregnancies affected by ITP are too low to warrant invasive testing or intervention.3–5,7,9 Thus, treatment of term pregnancies complicated by ITP remains controversial. Studies are limited by the rarity of disease, and observational reports might overrepresent poor neonatal outcomes.1,4,5 Decision analysis provides a methodical description of clinical pathways and outcomes based on current medical knowledge of treatment strategies and their probable outcomes. Our goal was to use decision analysis to create a model to aid clinical decision making for intrapartum treatment of term pregnancies complicated by ITP.
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Materials and Methods |
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). The analytic model was constructed specifically to address treatment of pregnant women who had ITP before pregnancy. Our decision analysis did not include risk estimates for neonatal alloimmune thrombocytopenia or gestational thrombocytopenia. The three management strategies were funipuncture at term, with delivery decisions based on fetal platelet count; no testing of fetal platelets, with delivery based on standard obstetric criteria; and intrapartum fetal scalp platelet sampling, with delivery decisions based on fetal platelet count. Those strategies comprise the initial branches of the decision tree model.
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Model Description
Funipuncture, fetal scalp sampling, and no-testing scenarios are characterized theoretically as follows (Figure 1
). A woman in the theoretic funipuncture cohort has funipuncture at term, with a risk of a complication that requires emergency cesarean (eg, fetal bradycardia or unremitting fetal hemorrhage).6,9,14,15,18–23 We assume that all fetuses of pregnancies complicated by ITP have the same risk of procedure-related complications regardless of the fetal platelet count. Of women who do not have procedure complications, most will have successful procedures, but some will not. Women who have unsuccessful funipuncture are delivered by cesarean because of unknown fetal platelet status. In agreement with the available literature, we define severe fetal thrombocytopenia as under 50,000 platelets per µL.1–3,6–8,12–18,24 If successful funipuncture shows severe fetal thrombocytopenia, the neonate is delivered by cesarean, but if funipuncture indicates a fetal platelet count over 50,000/µL, a trial of labor is attempted. Not all trials of labor successfully result in a vaginal delivery. We estimated the probability of trial of labor failure (ie, cesarean delivery rate) from the United States National Center for Health Statistics.25
A woman in the theoretic fetal scalp sampling cohort has intrapartum fetal scalp sampling, which is not always feasible because of unfavorable cervical status or fetal position.8,12,14 Neonates are delivered by cesarean if fetal scalp sampling is unsuccessful because fetal platelet status is unknown before delivery. If fetal scalp sampling is successful and severe fetal thrombocytopenia is detected, the infant is delivered by cesarean. If fetal scalp sampling shows a platelet count over 50,000/µL, a trial of labor is attempted. Because we defined platelet sampling-related complications as those necessitating immediate cesarean delivery, we assume that no procedure-related complications occur with fetal scalp sampling.18 Fetal scalp sampling is a highly sensitive test for severe thrombocytopenia, but only moderately specific, resulting in false-positive tests.4,12,16–18,26
A woman in the theoretic no-testing cohort has neither funipuncture nor fetal scalp sampling. That strategy allows women to attempt a trial of labor. A cesarean is done only for obstetric indications, including a failed trial of labor.
Outcomes
In the base-case analysis, we used pathway probabilities to calculate an expected number of severely thrombocytopenic neonates delivered vaginally, and cesarean deliveries per 1000 pregnancies for each strategy. A pathway probability is the product of all probabilities in the clinical pathway leading to the outcome(s) of interest, in this case the number of severely thrombocytopenic neonates delivered vaginally and cesareans. In our model, the most favorable management strategy results in the fewest severely thrombocytopenic neonates delivered vaginally with the lowest overall cesarean rate. As a secondary outcome, we calculated an expected number of procedure-related complications for the funipuncture strategy, providing a means to estimate the number of complications per 1000 pregnancies, relative to the number of severely thrombocytopenic neonates averted from being delivered vaginally. To analyze the effect of each strategy on maternal well-being, a second decision tree was constructed to evaluate delivery-related morbidity. We defined clinically important maternal delivery complications as hemorrhage, blood transfusion, infection, or postpartum fever. We used pathway probabilities to calculate an expected number of postpartum maternal morbid events per 1000 women for each strategy.
Probabilities
Base-case probability point estimates and plausible ranges for uncertain events or probabilities were obtained by quantitative review of the medical literature (Table 1). Point estimates were calculated as mean probabilities weighted by study size. We searched the MEDLINE database (1966–1997) using the search terms "immune thrombocytopenia," "autoimmune thrombocytopenia," "idiopathic thrombocytopenia purpura," "immune thrombocytopenic purpura," and "pregnancy" to identify appropriate studies and augmented the search by reviewing their bibliographies. The probabilities were estimated primarily from retrospective observational studies because we did not find randomized trials investigating ITP in pregnancy. One meta-analysis was available for estimating risk of maternal postpartum morbidity. Studies were reviewed and included in the analysis if they contained subjects with established diagnoses of ITP predating pregnancy, and contained adequate information to estimate maternal and neonatal probabilities. Some groups of women were included in more than one publication. We screened manuscripts for duplication of subject data and eliminated dual publications to avoid including the same data twice in probability estimates. Unpublished studies and abstracts were excluded. Studies with fewer than ten subjects were excluded to minimize bias toward positive reporting.27 Probabilities for delivery method-specific risks for intracranial hemorrhage in neonates born of mothers with ITP were not available in the current literature; therefore, intracranial hemorrhage was not modeled as an end point in the analysis. Instead we used intermediate measures, namely, the number of severely thrombocytopenic neonates delivered vaginally and cesarean deliveries per strategy, as our primary end points. The probability ranges used in the sensitivity analyses were calculated as exact 95% confidence intervals (CI) of binomial proportions. The one exception was the range for the cesarean delivery rate, which was not calculated as a 95% CI but was derived from the wider (and more conservative) range found in the literature.
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, a description of their calculation shows the integrity of the decision model. The true underlying rate of severe fetal or neonatal thrombocytopenia at delivery in the maternal ITP population was estimated from reports of funipuncture and postpartum cord blood results.1,2,4–9,28 The probability of severe neonatal thrombocytopenia at delivery was not estimated using platelet counts at the second to fifth postpartum day nadir. The probability of funipuncture complications was estimated using studies on women with ITP.6,9,13–15,19–23,25 The rate of successful funipuncture was based on no more than two attempts.13–15,20,29 On the basis of current reports, we assumed that funipuncture had a sensitivity and specificity of 1.0 (a perfect test if successful) for predicting severe neonatal thrombocytopenia at delivery.6,14,15,26 Fetal scalp sampling was reported to result in falsely low platelet counts because of platelet clumping or dilution.4,12,16–18 Using literature on ITP and trial of labor, we estimated maternal delivery complication (postpartum morbidity) rates for vaginal delivery, elective cesarean, and cesarean after trial of labor.4,16,30–32
Sensitivity Analysis
Multiple one-way and two-way sensitivity analyses were used to test the effect of varying probability estimates across plausible ranges on determining the most desirable strategy. The assumption that funipuncture is a perfectly accurate test for detecting fetal thrombocytopenia was the only probability estimate not tested in the sensitivity analysis. To further examine the effect of multiple probability estimates on our results (ie, multiway sensitivity analysis), we constructed best-case and worst-case scenarios for each strategy to show maximum and minimum plausible effects on averting vaginal delivery of severely thrombocytopenic neonates while maintaining the lowest possible cesarean rate. For example, a best-case scenario for the no-testing strategy and a worst-case scenario for the funipuncture strategy were entered in the model to see if funipuncture remained preferable under extreme probability ranges that favored no testing. To create a worst-case scenario for funipuncture, we used the highest possible values (within the plausible range) for procedure complication and failure probabilities. To create a best-case scenario for the no-testing strategy, we used the highest plausible value for cesarean rate and the lowest plausible value for probability of severe neonatal thrombocytopenia. Similar iterative exercises were done for each strategy or pairs of strategies, creating and comparing best- and worst-case scenarios. Initially, the decision tree was altered with a best- or worst-case scenario of a single strategy. Then pairs of scenarios, one best-case and one worst-case scenario for each of two opposing strategies, were entered in the model simultaneously.
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Results |
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shows expected results for the base-case analysis, including number of severely thrombocytopenic neonates delivered vaginally, cesareans, procedure complications, and postpartum complications reported per 1000 pregnancies. The ratio of additional cesareans done per single, severely thrombocytopenic neonate averted from delivering vaginally also is reported for each strategy. When the two testing strategies (ie, funipuncture versus fetal scalp sampling) were compared, funipuncture was clearly favorable. The funipuncture strategy allowed no severely thrombocytopenic neonates to be delivered vaginally (as did the fetal scalp sampling strategy), and maintained a lower overall cesarean rate than fetal scalp sampling. Funipuncture had a lower false-positive rate and a superior procedure success rate, and so can guide delivery plans more consistently. Compared with the no-testing strategy, funipuncture markedly reduced the number of severely thrombocytopenic neonates delivered vaginally, with only a modest increase in cesarean rate. Approximately 1.9 additional cesarean deliveries were done to prevent one severely thrombocytopenic neonate from being delivered vaginally using funipuncture versus no testing in the base-case analysis. In contrast, the fetal scalp sampling strategy resulted in 5.9 additional cesarean deliveries for each severely thrombocytopenic neonate prevented from being delivered vaginally. As defined in the model, funipuncture was the only strategy that resulted in a baseline risk for procedure-related fetal complications necessitating immediate cesarean. The fetal risk for a procedure complication necessitating immediate delivery was relatively low (3%). Maternal postpartum morbidity risk was similar with funipuncture and no testing, but was over 1.5 times higher with fetal scalp sampling. The base-case analysis supports funipuncture in term pregnant women with ITP if fetal platelet testing is used to guide delivery decisions.
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and 4). Table 3 summarizes the most pertinent results of the portion of the multiway sensitivity analysis in which best- or worst-case scenario of a single strategy was implemented. The worst-case funipuncture scenario resulted in a higher total number of cesarean deliveries compared with the base-case analysis; however, even with the increase in cesarean rate, the number of additional cesareans done to prevent one severely thrombocytopenic neonate from being delivered vaginally was still low at 2.7. There were similar results in the no-testing best-case scenario. In that scenario, even when all probabilities were in favor of no testing, the number of additional cesareans done to avert one severely thrombocytopenic neonate from being delivered vaginally using funipuncture was still low at 1.9. Throughout best- and worst-case scenarios for all three strategies, fetal scalp sampling was the least favorable strategy, offering no advantage over funipuncture in preventing severely thrombocytopenic neonates from being delivered vaginally, and carrying a substantially higher cesarean rate and maternal morbidity risk. Table 4 shows the most relevant results of simultaneously implementing the best-case scenario of one strategy and the worst-case scenario of an opposing strategy. When the best-case scenario for no testing and the worst-case scenario for funipuncture were combined, the probability estimates for cesarean delivery, underlying fetal thrombocytopenia, funipuncture success, and funipuncture complications are all maximally shifted in favor of no testing. Even when scenarios that impede funipuncture and favor no testing were combined, the number of additional cesareans done to prevent one severely thrombocytopenic neonate from delivering vaginally using funipuncture remained stable and low at 2.8.
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Discussion |
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Rates of severely thrombocytopenic neonates delivered vaginally, cesarean delivery, funipuncture complications, and maternal morbidity were identified as the model outcomes, based on concerns of using different management strategies and on availability of data for probability estimates. When the two fetal platelet-testing procedures were compared, funipuncture was clearly superior to fetal scalp sampling. Funipuncture prevented all severely thrombocytopenic neonates from being delivered vaginally while maintaining a much lower overall cesarean rate than fetal scalp sampling. Maternal postpartum morbidity was lower in the funipuncture strategy compared with the fetal scalp sampling strategy. Compared with no testing, funipuncture markedly decreased the number of severely thrombocytopenic neonates delivered vaginally, with only a modest increase in the cesarean rate. Funipuncture also had a risk for maternal postpartum morbidity similar to no testing, and a relatively low risk of funipuncture-related fetal complications. Those quantified outcomes of different clinical pathways can be weighed against potential ITP-related adverse neonatal outcomes in clinical decisions on whether, or how, to use fetal platelet testing.
An important finding of our study was that the results were stable across all probability ranges tested in the one-way and multiway sensitivity analyses. Of the two testing strategies, funipuncture consistently resulted in a smaller increase in overall cesarean rate while preventing all severely thrombocytopenic neonates from being delivered vaginally. The best-case and worst-case scenarios for each strategy did not alter our conclusions, indicating a robust decision model. That the decision model was not sensitive to plausible changes in probabilities was important because most probability estimates were based on observational studies rather than randomized, controlled trials or meta-analyses.
Our decision analysis was not without limitations. The results are not generalizable to pregnant women of all gestations. Treatment of premature gestations complicated by premature labor and ITP was not addressed. Probability estimates were established for term gestations only. Our model was designed to address decision making in women with a prepregnancy history of ITP, thus, treatment of women who present with thrombocytopenia during pregnancy cannot be inferred from it. Not all medical centers do funipuncture; therefore, our conclusions might not apply to women without access to tertiary care centers. Another aspect of clinical decision making not addressed by our model was patient preference. Our analysis assumed that women value preventing a severely thrombocytopenic neonate from being delivered vaginally and cesarean equally. If preferences are different, model outcomes might be altered, making clinical application of our results more difficult.
Interpretation of the results of this analysis was limited because we had to use intermediate measures (rates of severely thrombocytopenic neonates delivered vaginally and by cesarean) as model outcomes rather than the desired health outcome because no data were available on delivery mode-specific risk of intracranial hemorrhage. Because we did not use intracranial hemorrhage as an outcome in the decision model, some might question its validity. We strongly believe that it does not limit the model’s utility. The model explicitly shows the factors needed to make clinical decisions in selecting a delivery method while acknowledging that those decisions must be made without information on risk of intracranial hemorrhage. We did not believe it useful to incorporate a guess about the likelihood or magnitude of a protective effect of cesarean delivery into the decision model. Using rates of severely thrombocytopenic neonates delivered vaginally and cesarean deliveries as outcomes, and making that trade-off explicit, clinicians can synthesize the available medical knowledge to make a methodical decision about intrapartum treatment of pregnancies complicated by ITP. The clinician and subject must be aware that by using trade-offs in this analysis, one must speculate about the plausibility and magnitude that intracranial hemorrhage risk is decreased by cesarean delivery. A numerical example might help illustrate such a supposition. Risk of severe perinatal hemorrhage was estimated at 0.5–3.0% in neonates born with severe thrombocytopenia.3,9,24 Assume that the true incidence of hemorrhage is 1% and that cesarean delivery can prevent half of those bleeding episodes. Compared with no testing, using funipuncture would decrease the incidence of severe neonatal hemorrhage from eight to four per 10,000 infants at a cost of 390 additional cesareans, 20 additional maternal delivery complications, and 75 funipuncture-related neonatal complications for each hemorrhagic event prevented. Physicians and women will have different opinions about the importance of those risks and benefits and the plausibility that cesarean delivery provides a protective effect. One must incorporate preferences regarding risk of intracranial hemorrhage and the subsequent long-term disabilities versus the maternal risks of cesarean delivery and neonatal risks of platelet testing.
Our results suggest that fetal scalp sampling for intrapartum management of pregnancies complicated by ITP should be abandoned. If testing for fetal thrombocytopenia is done, it should be done by funipuncture. Outcomes of this decision model might help in clinical decisions about whether to pursue fetal platelet testing in the pregnancies complicated by ITP.
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Footnotes |
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Received September 9, 1998. Received in revised form December 9, 1998. Accepted January 7, 1999.
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References |
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