The association between iron deficiency and outcomes: a secondary analysis of the intravenous iron therapy to treat iron deficiency anaemia in patients undergoing major abdominal surgery (PREVENTT) trial

In the intravenous iron therapy to treat iron deficiency anaemia in patients undergoing major abdominal surgery (PREVENTT) trial, the use of intravenous iron did not reduce the need for blood transfusion or reduce patient complications or length of hospital stay. As part of the trial protocol, serum was collected at randomisation and on the day of surgery. These samples were analysed in a central laboratory for markers of iron deficiency. We performed a secondary analysis to explore the potential interactions between pre-operative markers of iron deficiency and intervention status on the trial outcome measures. Absolute iron deficiency was defined as ferritin <30 μg.l^-1 ; functional iron deficiency as ferritin 30-100 μg.l^-1 or transferrin saturation < 20%; and the remainder as non-iron deficient. Interactions were estimated using generalised linear models that included different subgroup indicators of baseline iron status. Co-primary endpoints were blood transfusion or death and number of blood transfusions, from randomisation to 30 days postoperatively. Secondary endpoints included peri-operative change in haemoglobin, postoperative complications and length of hospital stay. Most patients had iron deficiency (369/452 [82%]) at randomisation; one-third had absolute iron deficiency (144/452 [32%]) and half had functional iron deficiency (225/452 [50%]). The change in pre-operative haemoglobin with intravenous iron compared with placebo was greatest in patients with absolute iron deficiency, mean difference 8.9 g.l^-1 , 95%CI 5.3-12.5; moderate in functional iron deficiency, mean difference 2.8 g.l^-1 , 95%CI -0.1 to 5.7; and with little change seen in those patients who were non-iron deficient. Subgroup analyses did not suggest that intravenous iron compared with placebo reduced the likelihood of death or blood transfusion at 30 days differentially across subgroups according to baseline ferritin (p = 0.33 for interaction), transferrin saturation (p = 0.13) or in combination (p = 0.45), or for the number of blood transfusions (p = 0.06, 0.29, and 0.39, respectively). There was no beneficial effect of the use of intravenous iron compared with placebo, regardless of the metrics to diagnose iron deficiency, on postoperative complications or length of hospital stay.

When does obstetric coagulopathy occur and how do I manage it?

Anticipating obstetric coagulopathy is important when obstetric anaesthetists are involved in the clinical management of women with postpartum haemorrhage. Although the incidence of coagulopathy in women with postpartum haemorrhage is low, significant hypofibrinogenaemia is associated with major haemorrhage-related morbidity and thus early identification and treatment is essential to improve outcomes. Point-of-care viscoelastic haemostatic assays, including thromboelastography and rotational thromboelastometry, provide granular information about alterations in clot formation and hypofibrinogenaemia, allow near-patient interpretation of coagulopathy, and can guide goal-directed treatment. If these assays are not available, anaesthetists should closely monitor the maternal coagulation profile with standard laboratory testing during the active phase of postpartum bleeding in order to rule coagulopathy 'in or out', decide if pro-haemostatic therapies are indicated, and assess the response to haemostatic support.

Identifying late-onset fetal growth restriction by measuring circulating placental RNA in the maternal blood at 28 weeks' gestation

BACKGROUND

Late-onset fetal growth restriction (FGR) is often undetected prior to birth, which puts the fetus at increased risk of adverse perinatal outcomes including stillbirth.

OBJECTIVE

Measuring RNA circulating in the maternal blood may provide a noninvasive insight into placental function. We examined whether measuring RNA in the maternal blood at 26-30 weeks' gestation can identify pregnancies at risk of late-onset FGR. We focused on RNA highly expressed in placenta, which we termed "placental-specific genes."

STUDY DESIGN

This was a case-control study nested within a prospective cohort of 600 women recruited at 26-30 weeks' gestation. The circulating placental transcriptome in maternal blood was compared between women with late-onset FGR (<5th centile at >36+6 weeks) and gestation-matched well-grown controls (20-95th centile) using microarray (n = 12). TaqMan low-density arrays, reverse transcription-polymerase chain reaction (PCR), and digital PCR were used to validate the microarray findings (FGR n = 40, controls n = 80).

RESULTS

Forty women developed late-onset FGR (birthweight 2574 ± 338 g, 2nd centile) and were matched to 80 well-grown controls (birthweight 3415 ± 339 g, 53rd centile, P < .05). Operative delivery and neonatal admission were higher in the FGR cohort (45% vs 23%, P < .05). Messenger RNA coding 137 placental-specific genes was detected in the maternal blood and 37 were differentially expressed in late-onset FGR. Seven were significantly dysregulated with PCR validation (P < .05). Activating transcription factor-3 messenger RNA transcripts were the most promising single biomarker at 26-30 weeks: they were increased in fetuses destined to be born FGR at term (2.1-fold vs well grown at term, P < .001) and correlated with the severity of FGR. Combining biomarkers improved prediction of severe late-onset FGR (area under the curve, 0.88; 95% CI 0.80-0.97). A multimarker gene expression score had a sensitivity of 79%, a specificity of 88%, and a positive likelihood ratio of 6.2 for subsequent delivery of a baby <3rd centile at term.

CONCLUSION

A unique placental transcriptome is detectable in maternal blood at 26-30 weeks' gestation in pregnancies destined to develop late-onset FGR. Circulating placental RNA may therefore be a promising noninvasive test to identify pregnancies at risk of developing FGR at term.

A safety checklist for transoesophageal echocardiography from the British Society of Echocardiography and the Association of Cardiothoracic Anaesthetists

The World Health Organisation (WHO) launched the Surgical Safety Checklist in 2008. The introduction of this checklist resulted in a significant reduction in the incidence of complications and death in patients undergoing surgery. Consequently, the WHO Surgical Safety checklist is recommended for use by the National Patient Safety Agency for all patients undergoing surgery. However, many invasive or interventional procedures occur outside the theatre setting and there are increasing requirements for a safety checklist to be used prior to such procedures. Transoesophageal echocardiography (TOE) is an invasive procedure and although generally considered to be safe, it carries the risk of serious and potentially life-threatening complications. Strict adherence to a safety checklist may reduce the rate of significant complications during TOE. However, the standard WHO Surgical Safety Checklist is not designed for procedures outside the theatre environment and therefore this document is designed to be a procedure-specific safety checklist for TOE. It has been endorsed for use by the British Society of Echocardiography and the Association of Cardiothoracic Anaesthetists.

Risk factors for high and low placental weight

BACKGROUND

Placental weight is an independent predictor of adverse perinatal outcome. However, risk factors for high and low placental weight are poorly understood. The objective of this study was to identify maternal, placental, and umbilical cord determinants of placental weight, before and after accounting for birthweight.

METHODS

This cohort study of 87,600 singleton births at the Royal Victoria Hospital in Montreal, Canada assessed the relationship between maternal, placental, and umbilical cord characteristics and placental weight (standardised for sex and gestational age). We separately examined risk factors for high (z-score >+1) and low (z-score <-1) placental weight. Multivariable logistic regression was used to study associations after adjusting for confounders and further adjusting for birthweight.

RESULTS

Chronic hypertension was associated with low placental weight {relative risk (RR) 2.1 [95% confidence interval (CI) 1.8, 2.4] and 1.8 [95% CI 1.5, 2.1] before and after accounting for birthweight}, while pre-eclampsia was associated with low placenta weight before, but not after adjustment for birthweight. Anaemia and gestational diabetes were linked with high placental weight (RRs 1.2-1.4, respectively) before and after adjustment for birthweight, while smoking was linked with high placental weight only after adjustment for birthweight (RR 1.4 [95% CI 1.3, 1.5]). Placental and cord determinants of high placental weight included chorioamnionitis, chorangioma/chorangiosis, circumvallate placenta, marginal cord insertion, and other cord abnormalities.

CONCLUSIONS

The broad range of risk factors for high placental weight suggests multiple aetiologic pathways. Future work should seek to understand the pathways by which the placenta adapts to unfavourable intrauterine conditions, which may provide insights into potential therapies.

Smoking in preeclamptic women is associated with higher birthweight for gestational age and lower soluble fms-like tyrosine kinase-1 levels: a nested case control study

BACKGROUND

Smoking paradoxically increases the risk of small-for-gestational-age (SGA) birth but protects against preeclampsia. Some studies have reported a "U-shaped" distribution of fetal growth in preeclamptic pregnancies, but reasons for this are unknown. We investigated whether cigarette smoking interacts with preeclampsia to affect fetal growth, and compared levels of soluble fms-like tyrosine kinase-1 (sFlt-1), a circulating anti-angiogenic protein, in preeclamptic smokers and non-smokers.

METHODS

From a multicenter cohort of 5337 pregnant women, we prospectively identified 113 women who developed preeclampsia (cases) and 443 controls. Smoking exposure was assessed by self-report and maternal hair nicotine levels. Fetal growth was assessed as z-score of birthweight for gestational age (BWGA). sFlt-1 was measured in plasma samples collected at the 24-26-week visit.

RESULTS

In linear regression, smoking and preeclampsia were each associated with lower BWGA z-scores (β = -0.29; p = 0.008, and β = -0.67; p < 0.0001), but positive interaction was observed between smoking and preeclampsia (β = +0.86; p = 0.0008) such that smoking decreased z-score by -0.29 in controls but increased it by +0.57 in preeclampsia cases. Results were robust to substituting log hair nicotine for self-reported smoking and after adjustment for confounding variables. Mean sFlt-1 levels were lower in cases with hair nicotine levels above vs. below the median (660.4 pg/ml vs. 903.5 pg/ml; p = 0.0054).

CONCLUSIONS

Maternal smoking seems to protect against preeclampsia-associated fetal growth restriction and may account, at least partly, for the U-shaped pattern of fetal growth described in preeclamptic pregnancies. Smoking may exert this effect by reducing levels of the anti-angiogenic protein sFlt-1.

Non-stress-related factors associated with maternal corticotrophin-releasing hormone (CRH) concentration

During pregnancy, most maternal corticotrophin-releasing hormone (CRH) is secreted by the placenta, not the hypothalamus. Second trimester maternal CRH concentration is robustly associated with the subsequent risk of preterm birth, and it is often assumed that physiological and/or psychological stress stimulates placental CRH release. Evidence supporting the latter assumption is weak, however, and other factors affecting maternal CRH have received little attention from investigators. We carried out a case-control study nested within a large, multicentre prospective cohort of pregnant women to examine potential 'upstream' factors associated with maternal CRH concentration measured at 24-26 weeks of gestation. The predictors studied included maternal age, parity, birthplace (as a proxy for ethnic origin), pre-pregnancy body mass index, height, smoking, bacterial vaginosis and vaginal fetal fibronectin (FFN) concentration. Women with high (above the median) plasma CRH concentration were significantly less likely to have been born in Sub-Saharan Africa or the Caribbean, less likely to be overweight or obese, and more likely to be smokers. Associations with maternal birthplace and BMI persisted in logistic regression analyses controlling for potential confounding variables and when restricted to term controls. A strong (but imprecise and statistically non-significant) association was also observed with high vaginal FFN concentration. Further studies are indicated both in animal models and human populations to better understand the biochemical and physiological pathways to CRH secretion and their aetiological role, if any, in preterm birth.

Investigating socio-economic disparities in preterm birth: evidence for selective study participation and selection bias

Selective study participation can theoretically lead to selection bias. We explored this issue in the context of a multicentre cohort study of socio-economic disparities in preterm birth. Women with singleton pregnancies were recruited from four large Montreal maternity hospitals and invited to return for an interview, vaginal examination and venepuncture at 24-26 weeks of gestation. We compared the observed preterm birth rate (ultrasound confirmed) among the 5146 cohort women to that expected based on all 108 724 Montreal Census Metropolitan Area (CMA) singleton births for 1998-2000. The observed preterm birth rate in the study cohort was 5.1%, compared with 6.3% in the CMA (P < 0.001) (unadjusted morbidity ratio [95% CI] = 0.80 [0.71, 0.90]). Within each stratum of maternal education and neighbourhood income (the latter based on postal code matched links to the 2001 Canadian census), cohort women had substantially lower rates of preterm birth than women from the CMA. No significant association between socio-economic status (SES) and preterm birth was observed in the study cohort, except among 'indicated' (non-spontaneous) cases. The association between neighbourhood income and preterm birth was biased to the null in the study cohort, with adjusted odds ratios in the poorest vs. richest quintiles of 1.01 [0.63, 1.64] in the cohort vs. 1.28 [1.18, 1.39] in the CMA, although no such bias was observed for the association with maternal education assessed at the individual level. We speculate that the lower-than-expected preterm birth rate and attenuated association between neighbourhood income and preterm birth may be related to selective participation by women more psychologically invested in their pregnancies. Investigators should consider the potential for biased associations in pregnancy/birth cohort studies, especially associations based on SES or race/ethnicity, and carry out sensitivity analyses to gauge their effects.

Stress pathways to spontaneous preterm birth: the role of stressors, psychological distress, and stress hormones

The authors investigated a large number of stressors and measures of psychological distress in a multicenter, prospective cohort study of spontaneous preterm birth among 5,337 Montreal (Canada)-area women who delivered from October 1999 to April 2004. In addition, a nested case-control analysis (207 cases, 444 controls) was used to explore potential biologic pathways by analyzing maternal plasma corticotrophin-releasing hormone (CRH), placental histopathology, and (in a subset) maternal hair cortisol. Among the large number of stress and distress measures studied, only pregnancy-related anxiety was consistently and independently associated with spontaneous preterm birth (for values above the median, adjusted odds ratio = 1.8 (95% confidence interval: 1.3, 2.4)), with a dose-response relation across quartiles. The maternal plasma CRH concentration was significantly higher in cases than in controls in crude analyses but not after adjustment (for concentrations above the median, adjusted odds ratio = 1.1 (95% confidence interval: 0.8, 1.6)). In the subgroup (n = 117) of participants with a sufficient maternal hair sample, hair cortisol was positively associated with gestational age. Neither maternal plasma CRH, hair cortisol, nor placental histopathologic features of infection/inflammation, infarction, or maternal vasculopathy were significantly associated with pregnancy-related anxiety or any other stress or distress measure. The biologic pathways underlying stress-induced preterm birth remain poorly understood.

Vasculopathic and thrombophilic risk factors for spontaneous preterm birth

BACKGROUND

Mothers who give birth to preterm infants are at increased risk of mortality from coronary heart disease and stroke, but the biological pathways underlying these associations have not been explored.

METHODS

We carried out a case-control study nested in a large (n = 5337) prospective, multicentre cohort. All cohort women had an interview, examination and venipuncture at 24-26 weeks. Frozen plasma samples in spontaneous preterm births (n = 207) and 444 term controls were analysed for plasma homocysteine, folate, cholesterol (total, low-density lipoprotein and high-density lipoprotein) and thrombin-antithrombin (TAT) complexes. DNA was extracted and analysed for seven gene polymorphisms involved in thrombophilia or folate or homocysteine metabolism. Fresh placentas were fixed, stained and blindly assessed for histologic evidence of infarction and decidual vasculopathy.

RESULTS

High (above the median) plasma homocysteine and HDL cholesterol were significantly and independently associated with the risk of spontaneous preterm birth [adjusted odds ratios (OR)s = 1.9 (95% 1.1-3.3) and 0.5 (0.3-0.9), respectively]. A higher proportion of women with high homocysteine concentrations had decidual vasculopathy [(13.0 vs 6.8%; OR = 1.9 (1.1-3.5)], although the positive association between decidual vasculopathy and preterm birth did not achieve statistical significance [OR = 1.5 (0.9-2.7)]. No significant associations were observed with the DNA polymorphisms or with plasma TAT or folate levels.

CONCLUSIONS

Similar vasculopathic risk factors may underlie preterm birth and adult coronary heart disease and stroke.

Inherited thrombophilia and preeclampsia within a multicenter cohort: the Montreal Preeclampsia Study

OBJECTIVE

We sought to evaluate the association between inherited thrombophilia and preeclampsia.

STUDY DESIGN

From a multicenter cohort of 5337 pregnant women, we prospectively identified 113 women who developed preeclampsia and selected 443 control subjects who did not have preeclampsia or nonproteinuric gestational hypertension. Blood samples were tested for DNA polymorphisms affecting thrombophilia (factor V Leiden mutation, prothrombin G20210A mutation, methylenetetrahydrofolate reductase C677T polymorphism), homocysteine, and folate levels, and placentae underwent pathological evaluation.

RESULTS

Thrombophilia was present in 14% of patients and 21% of control subjects (adjusted logistic regression odds ratio, 0.6; 95% confidence interval, 0.3-1.3). Placental underperfusion was present in 63% of patients vs 46% of control subjects (P < .001) and was more frequent in women with folate levels in the lowest quartile (P = .04), but was not associated with thrombophilia.

CONCLUSION

We did not find evidence to support an association between inherited thrombophilia and increased risk of preeclampsia. Placental underperfusion is associated with preeclampsia, but this does not appear to be consequent to thrombophilia.

Intra- and interobserver agreement and statistical clustering of placental histopathologic features relevant to preterm birth

OBJECTIVE

Many previous studies of agreement in identifying placental histopathologic lesions have been based on small sample sizes, and none has examined whether individual histologic features cluster robustly together within and between observers.

STUDY DESIGN

We studied 767 placental specimens from case-control studies of preterm birth and preeclampsia nested within a prospective cohort of pregnant women recruited from 4 large Montreal maternity hospitals. The specimens were fixed, embedded, stained, and examined using a standardized protocol; a 10% random sample (n = 81) was then blindly reexamined at least 6 months later by the same pathologist and a second pathologist.

RESULTS

Intra- and interobserver agreement were high (kappa > or = 0.50) for membrane inflammation, funisitis, and umbilical cord vasculitis, and these 3 features were robustly clustered statistically, consistent with an underlying mechanism of ascending infection. Agreement and clustering were also high or moderate for features of placental underperfusion: infarction, decidual vasculopathy, and syncytial knotting.

CONCLUSION

Our results should help researchers to interpret future findings relating placental histopathology to preterm birth, preeclampsia, and other adverse pregnancy outcomes, and to their etiologic determinants and causal pathways.

The Effect of Computer-Assisted Evaluation of Labor on Cesarean Rates

Dystocia, or slow labor, is the leading cause of first-time cesarean sections. Current diagnostic guidelines for dystocia are vague, and there is no clear postoperative confirmatory evidence to assess the correctness of this diagnosis. For several decades, various professional organizations have indicated that cesarean rates could be lowered safely and have recommended levels that are far below national averages. The three major factors, of roughly equal importance, associated with cesarean for slow labor are the baby's weight, the mother's height, and the threshold at which the physician believes it is reasonable to intervene. The last is the only modifiable factor, and quality programs are a major part of changing medical behavior. By using two study designs, the effect of a mathematical method for evaluating labor progress on the rate of cesarean section was measured. In the prospective randomized clinical trial, the relative risk of cesarean in the experimental group was unchanged at 1.04. In the pretest-posttest analysis, the rates fell from 19.54% to 17.04% at 6 months and 16.62% at 12 months.

Why are babies getting bigger? Temporal trends in fetal growth and its determinants

OBJECTIVES

To describe temporal trends in fetal "growth" and to examine the roles of sociodemographic, anthropometric, and other determinants.

STUDY DESIGN

Hospital-based cohort study of 61,437 nonmalformed singleton live births at 22 to 43 weeks' gestational age. Four main measures were examined: (1) birth weight, (2) birth weight-for-gestational-age Z score, (3) small-for-gestational-age (SGA), and (4) large-for-gestational age (LGA), with the latter 3 measures based on a recently developed population-based Canadian reference. Gestational age was based on the last normal menstrual period if confirmed (+/- 1 week) by early ultrasonogram.

RESULTS

The mean birth weight and Z score increased significantly (P <.0001) among infants > or =37 weeks, with a corresponding reduction in % SGA and a rise in % LGA. No consistent trends were seen among births 34 to 36 or < or =33 weeks. When simultaneous changes in maternal prepregnancy body mass index, gestational weight gain, height, cigarette smoking, and other clinical and sociodemographic factors were controlled by using multiple logistic regression, the temporal trends for term infants were no longer evident.

CONCLUSIONS

Increases in maternal anthropometry, reduced cigarette smoking, and changes in sociodemographic factors have led to an increase in the weight of infants born at or after term.

Fetal health surveillance in labour

OBJECTIVE

This guideline defines the standards pertaining to the application and documentation of fetal surveillance in labour that will decrease the incidence of birth asphyxia while maintaining the lowest possible rate of obstetrical intervention. Both high- and low-risk obstetrical populations are considered. It is intended that this guideline could be used by all persons providing intrapartum care in Canada, including nurses, physicians, and midwives.

OPTIONS

Consideration has been given to methods of fetal surveillance currently available in Canada, including intermittent auscultation, electronic fetal monitoring (alone and when paired with vibro-acoustic or scalp stimulation and fetal scalp blood sampling), the "admission strip," computerized heart rate analysis, fetal oxygen saturation monitoring, fetal electrocardiogram analysis, and near-infrared spectroscopy.

OUTCOMES

Short- and long-term outcomes were considered that may indicate the presence of birth asphyxia. The associated rates of operative or other labour interventions were also considered.

EVIDENCE

A comprehensive review of randomized controlled trials performed from 1995 to date and a search of the literature using Medline and the Cochrane Database of all new studies on fetal surveillance. The level of evidence has been determined using the criteria described by the Canadian Task Force on the Periodic Health Examination.

RECOMMENDATIONS

Part I: Standard Fetal Surveillance in Labour 1. Women in active labour should receive continuous close support from an appropriately trained professional. One-to-one nursing is recommended. (I-A) 2. Intermittent auscultation following an established protocol of surveillance and response (Figure 1) is the preferred method of fetal surveillance in healthy pregnancies in the active phase of labour. (I-A) 3. Labour induction requires close monitoring of uterine activity and fetal heart rate. (III-B) 4. In the presence of abnormal fetal heart rate characteristics detected by intermittent auscultation and unresponsive to resuscitative measures, increased surveillance by continuous electronic fetal monitoring or fetal scalp sampling or delivery should be instituted. (I-A) 5. Continuous intrapartum electronic fetal monitoring is recommended: a) for pregnancies where there is an increased risk of perinatal death, cerebral palsy, or neonatal encephalopathy (III-C) b) when oxytocin is being used for augmentation of labour (1-A) c) when oxytocin is being used for induction of labour (III-C). 6. With respect to continuous electronic fetal monitoring, all professionals must be familiar with the paper speed used in each case to avoid misinterpretation. The correct time should be recorded on the electronic fetal monitoring record. (III-C) 7. Electronic fetal monitoring records should be inspected and documented every 15 minutes in the active phase of labour and at least every 5 minutes in the second stage of labour. (III-C) 8. The timing of electronic fetal monitoring patterns should be determined in association with uterine contractions. The contraction frequency, duration, intensity, and resting tone should be assessed and documented. Abdominal palpation, a tocodynamometer, or an intrauterine pressure catheter may be used to facilitate the assessment. (III-C) 9. Practitioners should use standard terminology when describing fetal heart rate characteristics of an electronic fetal monitoring record. (III-C) 10. Fetal scalp blood sampling is recommended in association with electronic fetal monitoring patterns that are uninterpretable or non-reassuring, such as sustained minimal or absent variability, uncorrectable late decelerations, increasing fetal tachycardia, and abnormal FHR characteristics on auscultation. (II-3B) 11. The limited knowledge available on the use of labour admission tests warrants further research to establish the usefulness of this screening approach. (III-C) Part II: New Technologies for Fetal Surveillance in Labour 12. The use of computer-based algorithms alone to interpret fetal heart rate patterns is not recommended as a standard of care at the present time. (III-D) 13. Fetal pulse oximetry as an adjunct to electronic fetal heart monitoring in patients with non-reassuring HR status is not recommended as a standard of care at the present time. (III-D) 14. ST waveform analysis technology is under development but is not recommended as a standard of care at this time. (III-C) 15. Near-infrared spectroscopy as an adjunct to electronic fetal monitoring is currently not recommended as there is insufficient evidence to assess its efficacy in fetal surveillance. (III-D) 16. Further study of fetal pulse oximetry, ST waveform analysis, and near-infrared technology in clinical research settings is encouraged. (III-B) VALIDATION: This guideline was reviewed by the SOGC Clinical Practice Obstetrics Committee, Maternal Fetal Medicine Committee, and ALARM Committee, as well as by the Canadian Medical Protective Association.

SPONSOR

The Society of Obstetricians and Gynaecologists of Canada.

Socio-economic disparities in preterm birth: causal pathways and mechanisms

Preterm birth is the leading cause of infant mortality in industrialised societies. Its incidence is greatly increased among the socially disadvantaged, but the reasons for this excess are unclear and have been relatively unexplored. We hypothesise two distinct sets of causal pathways and mechanisms that may explain social disparities in preterm birth. The first set involves chronic and acute psychosocial stressors, psychological distress caused by those stressors, increased secretion of placental corticotropin releasing hormone (CRH), changes in sexual behaviours or enhanced susceptibility to bacterial vaginosis and chorioamnionitis, cigarette smoking or cocaine use, and decidual vasculopathy. The second hypothesised pathway is a gene-environment interaction based on a highly prevalent mutation in the gene for methylenetetrahydrofolate reductase (MTHFR), combined with low folate intake from the diet and from prenatal vitamin supplements, consequent hyperhomocysteinemia, and decidual vasculopathy. We propose to test these hypothesised pathways and mechanisms in a nested case-control study within a prospectively recruited and followed cohort of pregnant women with singleton pregnancies who deliver at one of four Montreal hospitals that serve an ethnically and socio-economically diverse population. Following recruitment during the late first or early second trimester, participating women are seen at 24-26 weeks, when a research nurse obtains a detailed medical and obstetric history; administers several scales to assess chronic and acute stressors and psychological function; obtains blood samples for CRH, red blood cell and plasma folate, homocysteine, and DNA for the MTHFR mutation; and performs a digital and speculum examination to measure cervical length and vaginal pH and to obtain swabs for bacterial vaginosis and fetal fibronectin. After delivery, each case (delivery at < 37 completed weeks following spontaneous onset of labour or prelabour rupture of membranes) and two controls are selected for placental pathological examination, hair analysis of cotinine, cocaine, and benzoylecgonine, and analysis of stored blood and vaginal specimens. Statistical analysis will be based on multiple logistic regression and structural equation modelling, with sequential construction of models of potential aetiological determinants and covariates to test the hypothesised causal pathways and mechanisms. The research we propose should improve understanding of the factors and processes that mediate social disparities in preterm birth. This improved understanding should help not only in developing strategies to reduce the disparities but also in suggesting preventive interventions applicable across the entire socio-economic spectrum.

Dystocia among women with symptomatic uterine rupture

OBJECTIVE

The purpose of this study was to analyze cervical dilatation patterns among women with uterine rupture by means of a mathematic model and to use the results to determine optimal intervention criteria.

STUDY DESIGN

This was a case-control review that compared a case patient group of 19 women with uterine rupture during labor with control groups with either no previous cesarean deliveries, vaginal birth after cesarean delivery, or failure of attempted vaginal birth after cesarean delivery. The mathematic model quantified dilatation and adjusted for conditions specific to each patient. Case patients were compared with matched control subjects by means of paired t tests, analysis of variance, odds ratios, and conditional logistic regression.

RESULTS

Dystocia was present in 31.6% to 47.4% of patients with uterine rupture, versus 2.6% to 13.2% of the control group with no previous cesarean deliveries (P< or =.001). The incidence of an arrest disorder among patients with uterine rupture was similar to that seen in the control group with failure of attempted vaginal birth after cesarean delivery. However, the interval from diagnosis to rupture or cesarean delivery was 5.5 +/- 3.3 hours among case patients with uterine rupture and 1.5 +/- 1.3 hours in the control group with failure of attempted vaginal birth after cesarean delivery.

CONCLUSION

When cervical dilatation was lower than the 10th percentile and was arrested for > or =2 hours, cesarean delivery would have prevented 42.1% of the cases of uterine rupture and resulted in excess 2.6% and 7.9% cesarean delivery rates among women with no previous cesarean deliveries and women with vaginal birth after cesarean delivery, respectively.

A multicenter controlled trial of fetal pulse oximetry in the intrapartum management of nonreassuring fetal heart rate patterns

OBJECTIVE

Recent developments permit the use of pulse oximetry to evaluate fetal oxygenation in labor. We tested the hypothesis that the addition of fetal pulse oximetry in the evaluation of abnormal fetal heart rate patterns in labor improves the accuracy of fetal assessment and allows safe reduction of cesarean deliveries performed because of nonreassuring fetal status.

STUDY DESIGN

A randomized, controlled trial was conducted concurrently in 9 centers. The patients had term pregnancies and were in active labor when abnormal fetal heart rate patterns developed. The patients were randomized to electronic fetal heart rate monitoring alone (control group) or to the combination of electronic fetal monitoring and continuous fetal pulse oximetry (study group). The primary outcome was a reduction in cesarean deliveries for nonreassuring fetal status as a measure of improved accuracy of assessment of fetal oxygenation.

RESULTS

A total of 1010 patients were randomized, 502 to the control group and 508 to the study group. There was a reduction of >50% in the number of cesarean deliveries performed because of nonreassuring fetal status in the study group (study, 4. 5%; vs. control, 10.2%; P =.007). However, there was no net difference in overall cesarean delivery rates (study, n = 147 [29%]; vs. control, 130 [26%]; P = .49) because of an increase in cesarean deliveries performed because of dystocia in the study group. In a blinded partogram analysis 89% of the study patients and 91% of the control patients who had a cesarean delivery because of dystocia met defined criteria for actual dystocia. There was no difference between the 2 groups in adverse maternal or neonatal outcomes. In terms of the operative intervention for nonreassuring fetal status, there was an improvement in both the sensitivity and the specificity for the study group compared with the control group for the end points of metabolic acidosis and need for resuscitation.

CONCLUSION

The study confirmed its primary hypothesis of a safe reduction in cesarean deliveries performed because of nonreassuring fetal status. However, the addition of fetal pulse oximetry did not result in an overall reduction in cesarean deliveries. The increase in cesarean deliveries because of dystocia in the study group did appear to result from a well-documented arrest of labor. Fetal pulse oximetry improved the obstetrician's ability to more appropriately intervene by cesarean or operative vaginal delivery for fetuses who were actually depressed and acidotic. The unexpected increase in operative delivery for dystocia in the study group is of concern and remains to be explained.

Are all growth-restricted newborns created equal(ly)?

BACKGROUND

Previous etiologic studies have defined intrauterine growth restriction (IUGR) based on a single cutoff.

OBJECTIVE

To assess the relative importance of known etiologic determinants for different degrees (mild versus severe) and timing (preterm versus term) of fetal growth restriction.

DESIGN

Hospital-based cohort study.

SETTING

Tertiary-care university hospital.

PARTICIPANTS

Sixty-five thousand two hundred eighty inborn singleton infants without major congenital anomalies delivered between January 1, 1978 and March 31, 1996.

MEASUREMENTS

Comparison of adjusted odds ratios (ORs) and 95% confidence intervals for mild IUGR (defined as birth weight 75% to <85% of the mean for gestational age, the latter cutoff equivalent to the 9.9th percentile for this cohort) and severe IUGR (<75% of mean, or 2.3rd percentile), after controlling for maternal age, education, marital status, and other potential determinants by means of multiple logistic regression.

RESULTS

Maternal prepregnancy overweight (body mass index [BMI] >26.0-29.0 kg/m2) and obesity (BMI >29.0 kg/m2) had stronger protective effects against mild IUGR than against severe IUGR, but most of the determinants showed the opposite pattern. This was especially true for pathologic determinants; ORs (and 95% confidence intervals) for severe versus mild IUGR were 18.5 (14.5-23.8) vs 4.6 (3.6-5.8) for severe pregnancy-induced hypertension (PIH), 3.5 (2.2-5.5) vs 2.3 (1. 5-3.4) for prepregnancy hypertension, and 3.4 (2.9-3.9) vs 2.2 (2. 0-2.4) for smoking >/=11 cigarettes/day. Primiparity, short stature, prepregnancy BMI, maternal weight gain, and cigarette smoking had significantly larger effects on term IUGR, whereas the effect of severe PIH was more than twice as large for preterm IUGR (OR = 9.7 [7.3-13.0]) as for term IUGR (OR = 4.0 [3.0-5.3]).

CONCLUSION

Pathologic determinants of IUGR such as prepregnancy and PIH and cigarette smoking predispose to more severe fetal growth retardation, and PIH in particular seems to do so before 37 weeks. Growth-restricted newborns are not, therefore, all created equal(ly).

The effect of maternal epidural analgesia on fetal oxygen saturation

OBJECTIVE

To observe fetal arteriolar oxygen saturation during maternal epidural analgesia.

DESIGN

An observation study of 27 epidural top-ups.

SETTING

Labour ward, St James's University Hospital and Leeds General Infirmary, Leeds University, UK.

SAMPLE

Seventeen fetuses in uncomplicated labour monitored with a N400 fetal pulse oximeter.

OUTCOME MEASURE

A change in fetal pulse oximetry reading following epidural analgesia.

RESULTS

There is no change in fetal oxygen saturation following an uncomplicated epidural top-up (F = 0.93; df 35 and 784).

CONCLUSION

An uneventful maternal epidural has no measurable effect on fetal oxygen saturation measured with a N400 pulse oximeter.

Comparing fetal pulse oximetry with scalp pH

OBJECTIVE

To determine whether pulse oximetry has the potential to replace scalp blood pH sampling in infants with abnormal cardiotocographs.

STUDY DESIGN

The average scalp oximetry reading in labor recorded with an experimental N400 system was compared with fetal scalp blood pH.

RESULTS

The average oximetry readings were unrelated to the pH of aerobically sampled fetal scalp blood. There was no subgroup of acidemic infants with a low oximetry reading.

CONCLUSION

Pulse oximetry readings with present technology do not reflect scalp pH. The equipment is improving, but at this time pulse oximetry is not a simple alternative for scalp capillary blood sampling.

The effect of uterine contractions on fetal oxygen saturation

OBJECTIVE

To find out what happens to fetal arteriolar oxygen saturation during a uterine contraction.

DESIGN

Prospective observational study.

SETTING

Labour ward, St James's University Hospital, Leeds.

SUBJECTS

Eighteen women in normal labour monitored with a fetal scalp surface pulse oximetry sensor, an intrauterine pressure catheter, and a head to cervix force transducer.

METHODS

The effect of intrauterine pressure and head to cervix force on fetal arteriolar oxygen saturation was examined using time series analysis and a regression model of 159 contractions.

OUTCOME MEASURE

Fetal oxygen saturation during a contraction.

RESULTS

The average oxygen saturation drops after a contraction. The greatest drop in oxygen saturation is reached 92 s after the peak of a contraction and takes approximately 1 min 30 s to recover (P = 0.036).

CONCLUSION

Uterine contractions during normal labour affect fetal oxygen saturation.

Fetal pulse oximetry: a new method of monitoring the fetus

Experimental pulse oximetry devices, similar to the existing systems used in adult and neonatal monitoring, can be used on the fetus to provide safe, and rapid information about oxygenation. They have been calibrated using fetal lambs and validated in human cross-sectional studies. Experiments have shown that fetal oxygen saturation decreases during normal labour, and drops after a uterine contraction especially with oxytocin-induced tachysystole. When the mother is given oxygen the fetal oxygen saturation increases. Readings are effected by caput and movement, and trends seem to be more meaningful than absolute values. Pulse oximetry can predict fetal outcome and a normal oxygen saturation result is specific for a good outcome perhaps even if the CTG is abnormal. However the technique is still experimental and there is insufficient data to support its use as a replacement for fetal blood sampling or a discriminator for an abnormal fetal heart trace.

The effect on fetal arteriolar oxygen saturation resulting from giving oxygen to the mother measured by pulse oximetry

OBJECTIVE

To determine if pulse oximetry could detect any changes in fetal arteriolar oxygen saturation resulting from maternal administration of oxygen.

DESIGN

A prospective study comparing study comparing the fetal pulse oximetry reading before and after giving 27% and 100% oxygen to the mother. The data were collected using an experimental pulse oximeter and a sensor specifically adapted to cope with the problems of fetal pulse oximetry.

SETTING

Labour ward, St. Jame's University Hospital, Leeds University, UK.

SUBJECTS

Twelve fetuses presenting by the vertex in normal uncomplicated labour.

MAIN OUTCOME MEASURES

The change in fetal arteriolar oxygen saturation recorded by the pulse oximeter in response to oxygen administration to the mother.

RESULTS

Twenty-seven percent oxygen increased the average fetal arteriolar oxygen saturation by 7.5%, the effect being reversed when the oxygen was withdrawn. One hundred percent oxygen increased fetal arteriolar oxygen saturation by 11% and when the oxygen was withdrawn oxygen saturation dropped by 10%. One hundred percent inspired maternal oxygen was more effective than 27%. The gradient of the fetal oxygen regression slope is steeper with 100% oxygen than 27% and it is steeper when oxygen is given compared to when it is withdrawn. This suggests that the fetus responds to the new placental oxygen gradient by accepting oxygen more rapidly than it gives it up. Using a quadratic regression model, it took 9 min for fetal oxygen saturation to reach its maximum value after giving the mother oxygen.

CONCLUSION

This study confirms that a pulse oximeter is able to measure an increase in fetal arteriolar oxygen saturation when oxygen is administered to the mother.

Do fetal pulse oximetry readings at delivery correlate with cord blood oxygenation and acidaemia?

OBJECTIVE

To assess the accuracy of a pulse oximeter in the fetus.

DESIGN

A prospective descriptive study, comparing oxygenation and acidaemia of cord blood with oxygen saturation in the arteries of the fetal scalp measured by a pulse oximeter just before delivery. The data were collected using an experimental pulse oximeter and a sensor specifically adapted to cope with the problems of fetal pulse oximetry.

SETTING

The labour ward in a teaching hospital.

SUBJECTS

Thirty seven Caucasian fetuses presenting by the vertex in normal uncomplicated labour.

MAIN OUTCOME MEASURE

Fetal pulse oximetry reading shortly before birth, umbilical cord oxygenation and pH, and Apgar scores.

RESULTS

Data of sufficient quality were obtained from 28 fetuses. There was a highly significant correlation between pulse oximetry reading and umbilical vein oxygen saturation r = 0.59, P = < 0.001). There was also a significant correlation between the pulse oximeter reading and cord blood pH (vein: r = 0.57, P = 0.002, artery: r = 0.63, P = 0.001). Apgar scores were not related to the oximetry results.

CONCLUSION

Pulse oximetry readings reflect fetal oxygenation at birth.

The effect of meconium on neonatal and fetal reflectance pulse oximetry

Reflectance probes are being developed for neonatal use and obstetricians are beginning to use reflectance pulse oximetry to monitor the fetus. When a reflectance probe was used to monitor the arterial oxygen saturation of a baby whose skin was stained with meconium an artificially low result was obtained. This is because meconium absorbs more red than infra-red light and acts as a red light filter between the vascular bed and the probe. This effect may be reproduced by interposing a red filter between a reflectance pulse oximetry probe and the skin. Obstetricians who use a pulse oximeter to assess the fetus through intact membranes will record an erroneously low result if they are stained with meconium. Similarly neonatologists should avoid placing a reflectance pulse oximetry probe on babies skin which is stained with meconium.