Emily F. Hamilton

Fetal Health Surveillance: Antepartum and Intrapartum Consensus Guideline

OBJECTIVE This guideline provides new recommendations pertaining to the application and documentation of fetal surveillance in the antepartum and intrapartum period that will decrease the incidence of birth asphyxia while maintaining the lowest possible rate of obstetrical intervention. Pregnancies with and without risk factors for adverse perinatal outcomes are considered. This guideline presents an alternative classification system for antenatal fetal non-stress testing and intrapartum electronic fetal surveillance to what has been used previously. This guideline is intended for use by all health professionals who provide antepartum and intrapartum care in Canada. OPTIONS Consideration has been given to all methods of fetal surveillance currently available in Canada. OUTCOMES Short- and long-term outcomes that may indicate the presence of birth asphyxia were considered. The associated rates of operative and other labour interventions were also considered. EVIDENCE A comprehensive review of randomized controlled trials published between January 1996 and March 2007 was undertaken, and MEDLINE and the Cochrane Database were used to search the literature for all new studies on fetal surveillance both antepartum and intrapartum. The level of evidence has been determined using the criteria and classifications of the Canadian Task Force on Preventive Health Care. SPONSOR This consensus guideline was jointly developed by the Society of Obstetricians and Gynaecologists of Canada and the British Columbia Perinatal Health Program (formerly the British Columbia Reproductive Care Program or BCRCP) and was partly supported by an unrestricted educational grant from the British Columbia Perinatal Health Program.

Maternal anthropometry and idiopathic preterm labor

Objective To assess the etiologic role of maternal short stature, low pre-pregnancy body mass index (BMI), and low rate of gestational weight gain in idiopathic preterm labor. Methods We carried out a three-center case-control study of 555 women with idiopathic onset of preterm labor (before 37 completed weeks), including two overlapping (ie, non-mutually exclusive) subsamples: cases with early preterm labor (before 34 completed weeks) and cases with recurrent preterm labor (before 37 completed weeks plus a history of prior preterm delivery or second-trimester miscarriage). Controls were matched to cases by race and smoking history. All subjects responded in person to questions about height, pre-pregnancy weight, gestational weight gain, and obstetric and sociodemographic histories. Results Maternal height, pre-pregnancy weight, and gestational weight gain demonstrated excellent test-retest reliability, with intra-class correlation coefficients of 0.97, 0.99, and 0.91, respectively. Based on matched analyses, women with a height of 157.5 cm or less had an increased risk of idiopathic preterm labor (odds ratio [OR] 1.85, 95% confidence interval [CI] 1.25–2.74), as did those with a prepregnancy BMI less than 19.8 kg/m2 (OR 1.63, 95% CI 1.09–2.44) or a gestational weight gain rate less than 0.27 kg/week (OR 1.74, 95% CI 1.16–2.62). Conditional logistic regression models containing all three anthropometric variables and controlling for parity, marital status, language, age, and education yielded virtually identical point estimates and CIs. Conclusion Maternal short stature, low pre-pregnancy BMI, and low rate of gestational weight gain may lead to shortened gestation by increasing the risk of idiopathic preterm labor.

Maternal age and primary cesarean section rates: A multivariate analysis

To study the effect of maternal age on primary cesarean section rates, 3458 consecutive deliveries were analyzed. The cesarean section rates in primiparous women less than 25, 25 to 34, and over 34 years of age were 13.1%, 18.5%, and 28.2%, respectively. A similarly dramatic rise with advancing maternal age was seen in multiparous women with rates of 3.4%, 4.7%, and 10.1%, respectively, in the three age groups. The strong association between cesarean section and maternal age persisted after multivariate adjustment for induction of labor, epidural anesthesia, meconium-stained amniotic fluid, and fetal distress, and thus these factors do not explain the relationship.

Classification of Normal and Hypoxic Fetuses From Systems Modeling of Intrapartum Cardiotocography

Recording of maternal uterine pressure (UP) and fetal heart rate (FHR) during labor and delivery is a procedure referred to as cardiotocography. We modeled this signal pair as an input-output system using a system identification approach to estimate their dynamic relation in terms of an impulse response function. We also modeled FHR baseline with a linear fit and FHR variability unrelated to UP using the power spectral density, computed from an auto-regressive model. Using a perinatal database of normal and pathological cases, we trained suport-vector-machine classifiers with feature sets from these models. We used the classification in a detection process. We obtained the best results with a detector that combined the decisions of classifiers using both feature sets. It detected half of the pathological cases, with very few false positives (7.5%), 1 h and 40 min before delivery. This would leave sufficient time for an appropriate clinical response. These results clearly demonstrate the utility of our method for the early detection of cases needing clinical intervention.

Comparison of 5 experts and computer analysis in rule-based fetal heart rate interpretation.

OBJECTIVE The purpose of this study was to measure agreement among 5 expert clinicians and a computerized method with the use of a strict fetal heart rate classification method. STUDY DESIGN Five providers independently scored 769 8-minute segments from the last 3 hours of 30 tracings with the use of a 5-tier color-coded framework that contains pattern descriptions and proposals for management. Computer analysis was performed with PeriCALM Patterns (PeriGen, Princeton, NJ) to detect and classify patterns. RESULTS The clinicians agreed exactly with the majority opinion in 57% (95% confidence interval [CI], 49-64%) of the segments and were within 1 color code in 89% (95% CI, 81-96%). The average proportion of agreement was 0.83 (95% CI, 0.73-0.94). Weighted Kappa scores averaged 0.58 (range, 0.48-0.68). The computer-based results were not statistically different: 0.87 and 0.52, respectively. CONCLUSION These 5 clinicians achieved moderate-to-substantial levels of agreement overall using a strictly defined method to classify fetal heart rate tracings. The result of the computerized method was similar to the conclusions of these clinicians.

Third- and fourth-degree perineal lacerations: defining high-risk clinical clusters

OBJECTIVE Statistical methods that measure the independent contribution of individual factors for third-/fourth-degree perineal laceration (TFPL) fall short when the clinician is faced with a combination of factors. Our objective was to demonstrate how a statistical technique, classification and regression trees (CART), can identify high-risk clinical clusters. STUDY DESIGN We performed multivariable logistic regression, and CART analysis on data from 25,150 term vaginal births. RESULTS Multivariable analyses found strong associations with the use of episiotomy, forceps, vacuum, nulliparity, and birthweight. CART ranked episiotomy, operative delivery, and birthweight as the more discriminating factors and defined distinct risk groups with TFPL rates that ranged from 0-100%. For example, without episiotomy, the rate of TFPL was 2.2%. In the presence of an episiotomy, forceps, and birthweight of >3634 g, the rate of TFPL was 68.9%. CONCLUSION CART showed that certain combinations held low risk, where as other combinations carried extreme risk, which clarified how choices on delivery options can markedly affect the rate of TFPL for specific mothers.

The limits of electronic fetal heart rate monitoring in the prevention of neonatal metabolic acidemia

BACKGROUND: Despite intensive efforts directed at initial training in fetal heart rate interpretation, continuing medical education, board certification/recertification, team training, and the development of specific protocols for the management of abnormal fetal heart rate patterns, the goals of consistently preventing hypoxia‐induced fetal metabolic acidemia and neurologic injury remain elusive. OBJECTIVE: The purpose of this study was to validate a recently published algorithm for the management of category II fetal heart rate tracings, to examine reasons for the birth of infants with significant metabolic acidemia despite the use of electronic fetal heart rate monitoring, and to examine critically the limits of electronic fetal heart rate monitoring in the prevention of neonatal metabolic acidemia. STUDY DESIGN: The potential performance of electronic fetal heart rate monitoring under ideal circumstances was evaluated in an outcomes‐blinded examination fetal heart rate tracing of infants with metabolic acidemia at birth (base deficit, >12) and matched control infants (base deficit, <8) under the following conditions: (1) expert primary interpretation, (2) use of a published algorithm that was developed and endorsed by a large group of national experts, (3) assumption of a 30‐minute period of evaluation for noncritical category II fetal heart rate tracings, followed by delivery within 30 minutes, (4) evaluation without the need to provide patient care simultaneously, and (5) comparison of results under these circumstances with those achieved in actual clinical practice. RESULTS: During the study period, 120 infants were identified with an arterial cord blood base deficit of >12 mM/L. Matched control infants were not demographically different from subjects. In actual practice, operative intervention on the basis of an abnormal fetal heart rate tracings occurred in 36 of 120 fetuses (30.0%) with metabolic acidemia. Based on expert, algorithm‐assisted reviews, 55 of 120 patients with acidemia (45.8%) were judged to need operative intervention for abnormal fetal heart rate tracings. This difference was significant (P=.016). In infants who were born with a base deficit of >12 mM/L in which blinded, algorithm‐assisted expert review indicated the need for operative delivery, the decision for delivery would have been made an average of 131 minutes before the actual delivery. The rate of expert intervention for fetal heart rate concerns in the nonacidemic control group (22/120; 18.3%) was similar to the actual intervention rate (23/120; 19.2%; P=1.0) Expert review did not mandate earlier delivery in 65 of 120 patients with metabolic acidemia. The primary features of these 65 cases included the occurrence of sentinel events with prolonged deceleration just before delivery, the rapid deterioration of nonemergent category II fetal heart rate tracings before realistic time frames for recognition and intervention, and the failure of recognized fetal heart rate patterns such as variability to identify metabolic acidemia. CONCLUSIONS: Expert, algorithm‐assisted fetal heart rate interpretation has the potential to improve standard clinical performance by facilitating significantly earlier recognition of some tracings that are associated with metabolic acidemia without increasing the rate of operative intervention. However, this improvement is modest. Of infants who are born with metabolic acidemia, only approximately one‐half potentially could be identified and have delivery expedited even under ideal circumstances, which are probably not realistic in current US practice. This represents the limits of electronic fetal heart rate monitoring performance. Additional technologies will be necessary if the goal of the prevention of neonatal metabolic acidemia is to be realized.

Fetal cephalometry by ultrasound as a screening procedure for the prenatal detection of Down's syndrome

Infants and children with Downs syndrome have a cephalic index (ratio of biparietal to occipitofrontal diameter) higher than that in normal children. To determine whether this difference is present and detectable by ultrasound measurement of the second‐trimester fetal head, we calculated the cephalic indices for 308 normal fetuses and eight fetuses with a 47,+21 karyotype. The mean cephalic index in the fetuses with Downs syndrome (0.829, SD 0.033) was indistinguishable from that in the normal fetuses (0.825, SD 0.042). These data suggest that the documented difference in mean cephalic index between liveborn children with Downs syndrome and normal control children is not detectable in the mid‐gestation fetus and that ultrasound cephalometry alone is unlikely to discriminate reliably between normal and affected fetuses.

Variable decelerations: do size and shape matter?

Objective: To determine the ability of variable decelerations and 8 subtypes, defined by size and shape, to discriminate tracings between babies with normal umbilical artery gases (N) and those with metabolic acidemia (MA). Methods: Tracings from the last 4 hours from N—3320 babies with base deficit levels under 8 mmol/L, and from MA—316 babies with base deficits over 12 mmol/L were analyzed using computerized pattern recognition. We created receiver operating characteristic curves and area under the curves (AUCs) for each deceleration subtype. Results: Only 3 subtypes showed significant discrimination: those with a prolonged duration (AUC 0.6109 P < 0.0001), loss of internal variability (AUC 0.5694 P < 0.0001) or with “sixties” criteria (AUC 0.5997 P < 0.0001). A variable deceleration met the sixties criteria if two or more of the following were present: depth was 60 bpm or more, lowest value was 60 or less, duration was 60 seconds or longer. All other subtypes were no better than chance. Conclusions: Finer gradation within the middle category of electronic fetal monitoring classification is needed because most tracings, including those from babies with MA, will be located in the Category II. This analysis identifies which variable decelerations have a significant association with MA and which do not.

Identification of the Dynamic Relationship Between Intrapartum Uterine Pressure and Fetal Heart Rate for Normal and Hypoxic Fetuses

Labor and delivery are routinely monitored electronically with sensors that measure and record maternal uterine pressure (UP) and fetal heart rate (FHR), a procedure referred to as cardiotocography (CTG). Delay or failure to recognize abnormal patterns in these recordings can result in a failure to prevent fetal injury. We address the challenging problem of interpreting intrapartum CTG in a novel way by modeling the dynamic relationship between UP (as an input) and FHR (as an output). We use a nonparametric approach to estimate the dynamics in terms of an impulse response function (IRF). We apply singular value decomposition to suppress noise, IRF delay, and memory estimation to identify the temporal extent of the response and surrogate testing to assess model significance. We construct models for a database of CTG recordings labeled by outcome, and compare the models during the last 3 h of labor as well as across outcome classes. The results demonstrate that the UP-FHR dynamics can be successfully modeled as an input-output system. Models for pathological cases had stronger, more delayed, and more predictable responses than those for normal cases. In addition, the models evolved in time, reflecting a clinically plausible evolution of the fetal state due to the stress of labor.