Determinants of the optimal time in gestation to initiate antenatal fetal testing: a decision-analytic approach

Epidemiology of stillbirths based on different gestational thresholds at a tertiary hospital

INTRODUCTION

The stillbirth rate (SBR) is an important public health indicator. We studied the distribution of maternal and fetal characteristics and time trends of the SBR at KK Women's and Children's Hospital (KKH), Singapore, from 2004 to 2016 based on various definitions of stillbirth.

METHODS

Data was obtained from the Data Warehouse and Stillbirth Reporting System of KKH from 2004 to 2016. SBRs were calculated based on three definitions (fetal deaths at ≥ 20 weeks, 24 weeks or 28 weeks of gestation per 1,000 total births) and were described with maternal and fetal characteristics, and by year.

RESULTS

From 2004 to 2016, the SBR declined by 44.7%, 25.5% and 18.9% based on Definitions I, II and III, respectively. The SBR at KKH in 2016 was 5.2 (Definition I), 4.1 (Definition II) and 3.0 (Definition III) per 1,000 total births. The SBR was significantly higher in women aged ≥ 35 years, nulliparas and female fetuses. The number of live births at 24-27+6 weeks of gestation was more than four times higher than that of stillbirths (822 vs. 176). There were 104 (12.7%) neonatal deaths during this gestation period, giving a high survival rate of 87.3%.

CONCLUSION

The SBR in KKH is relatively lower than that in other developed countries. There is a need to consider revising our hospital and national definitions of the stillbirth lower boundary from 28 weeks to 24 weeks of gestation. This would allow us to make better comparisons with other developed countries, in line with improvements in healthcare.

Factors Associated with Occurrence of Stillbirth before 32 Weeks of Gestation in a Contemporary Cohort

OBJECTIVE

We sought to quantify the distribution of stillbirths by gestational age (GA) in a contemporary cohort and to determine identifiable risk factors associated with stillbirth prior to 32 weeks of gestation.

STUDY DESIGN

Population-based case-control study of all stillbirths in the United States during the year 2014, utilizing vital statistics data, obtained from the National Center for Health Statistics. Distribution of stillbirths were stratified by 20 to 44 weeks of GA, in women diagnosed with stillbirth in the antepartum period. Pregnancy characteristics were compared between those diagnosed with stillbirth <32 versus ≥32 weeks of gestation. Multivariate logistic regression estimated the relative influence of various factors on the outcome of stillbirth prior to 32 weeks of gestation.

RESULTS

There were 15,998 nonlaboring women diagnosed with stillbirth during 2014 in the United States between 20 and 44 weeks. Of them, 60.1% (n = 9,618) occurred before antenatal fetal surveillance (ANFS) is typically initiated (<32 weeks) and 39.9% (n = 6,380) were diagnosed at ≥32 weeks. Women with stillbirth prior to 32 weeks were more likely to be of non-Hispanic Black race (29.0 vs. 23.9%, p < 0.001), nulliparous (53.8 vs. 50.6%, p = 0.001), have chronic hypertension (CHTN; 6.0 vs. 4.3%, p < 0.001), and fetal growth restriction as evidenced by small for GA (SGA < 10th%) birth weight (44.8 vs. 42.1%, p < 0.001) as opposed to women with stillbirth after 32 weeks. After adjustment, SGA birth weight (adjusted odds ratio [aOR] = 1.2, 95% confidence interval [CI]: 1.1-1.3), Black race (aOR = 1.2, 95% CI: 1.1-1.3), and CHTN (aOR = 1.3, 95% CI: 1.1-1.5) were associated with stillbirth prior to 32 weeks of gestation as opposed to stillbirth after 32 weeks.

CONCLUSION

More than 6 out of 10 stillbirths in this study occurred <32 weeks of gestation, before ANFS is typically initiated under American College of Obstetricians and Gynecologists recommendations. Among identifiable risk factors, CHTN, Black race, and fetal growth restriction were associated with higher risk of stillbirth before 32 weeks of gestation. Earlier ANFS may be warranted at in certain "at risk" women.

KEY POINTS

· Six out of 10 stillbirths occur before 32 weeks of gestation.. · We evaluated factors associated with stillbirth <32 weeks.. · Hypertension and fetal growth restriction were associated with early stillbirth..

Methods for Monitoring Risk of Hypoxic Damage in Fetal and Neonatal Brains: A Review

Fetal, perinatal, and neonatal asphyxia are vital health issues for the most vulnerable groups in human beings, including fetuses, newborns, and infants. Severe reduction in oxygen and blood supply to the fetal brain can cause hypoxic-ischemic encephalopathy (HIE), leading to long-term neurological disorders, including mental impairment and cerebral palsy. Such neurological disorders are major healthcare concerns. Therefore, there has been a continuous effort to develop clinically useful diagnostic tools for accurately and quantitatively measuring and monitoring blood and oxygen supply to the fetal and neonatal brain to avoid severe consequences of asphyxia HIE and neonatal encephalopathy. Major diagnostic technologies used for this purpose include fetal heart rate monitoring, fetus scalp blood sampling, ultrasound imaging, magnetic resonance imaging, X-ray computed tomography, and nuclear medicine. In addition, given the limitations and shortcomings of traditional diagnostic methods, emerging technologies such as near-infrared spectroscopy and photoacoustic imaging have also been introduced as stand-alone or complementary solutions to address this critical gap in fetal and neonatal care. This review provides a thorough overview of the traditional and emerging technologies for monitoring fetal and neonatal brain oxygenation status and describes their clinical utility, performance, advantages, and disadvantages.

Antepartum Fetal Surveillance: ACOG Practice Bulletin, Number 229

The goal of antepartum fetal surveillance is to reduce the risk of stillbirth. Antepartum fetal surveillance techniques based on assessment of fetal heart rate (FHR) patterns have been in clinical use for almost four decades and are used along with real-time ultrasonography and umbilical artery Doppler velocimetry to evaluate fetal well-being. Antepartum fetal surveillance techniques are routinely used to assess the risk of fetal death in pregnancies complicated by preexisting maternal conditions (eg, diabetes mellitus) as well as those in which complications have developed (eg, fetal growth restriction). The purpose of this document is to provide a review of the current indications for and techniques of antepartum fetal surveillance and outline management guidelines for antepartum fetal surveillance that are consistent with the best scientific evidence.

No. 197a-Fetal Health Surveillance: Antepartum Consensus Guideline

OBJECTIVE

This guideline provides new recommendations pertaining to the application and documentation of fetal surveillance in the antepartum 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 to what has been used previously. This guideline is intended for use by all health professionals who provide antepartum 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 antepartum. The level of evidence has been determined using the criteria and classifications of the Canadian Task Force on Preventive Health Care (Table 1).

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. RECOMMENDATION 1: FETAL MOVEMENT COUNTING: RECOMMENDATION 2: NON-STRESS TEST: RECOMMENDATION 3: CONTRACTION STRESS TEST: RECOMMENDATION 4: BIOPHYSICAL PROFILE: RECOMMENDATION 5: UTERINE ARTERY DOPPLER: RECOMMENDATION 6: UMBILICAL ARTERY DOPPLER.

Gestational age-specific neonatal morbidity among pregnancies complicated by advanced maternal age: a population-based retrospective cohort study

OBJECTIVE

Compare significant neonatal morbidity frequency differences in advanced maternal age (AMA) versus non-AMA pregnancies, assessing which gestational week is associated with the lowest morbidity risk.

METHODS

Population-based retrospective cohort study. Adverse neonatal outcome frequency differences were stratified by each week of gestation. Multivariate logistic regression estimated the relative risk (RR) of composite neonatal morbidity for women aged 35-39, 40-44, 45-49 and 50-55 versus 18-34 years, adjusted sequentially for relevant risk factors.

RESULTS

Neonatal morbidity decreased with each advancing week of term gestation, lowest at 39 weeks for all the groups. Adverse neonatal outcome risk for births to AMA women increased at 40 weeks: 35-39 years adjRR 1.12 [1.01-1.24] and ≥40 years 1.24 [1.01-1.52]. Each older maternal age category had increased risk for overall neonatal morbidity: 35-39 years adjRR 1.11 [95% CI 1.08-1.15], 40-44 years 1.21 [95% CI 1.14-1.29] and 45-49 years 1.34 [95% CI 1.05-1.69].

CONCLUSIONS

Lowest neonatal morbidity risk is at 39-week gestation with a significantly increased risk observed thereafter, especially in women ≥40 years.

Detection of fetal growth restriction in patients with chronic hypertension: is it feasible?

OBJECTIVE

To determine the utility of sonographic estimated fetal weight (EFW) in diagnosing intrauterine growth restriction (IUGR, birth weight < 10% for gestational age) in patients with chronic hypertension.

METHODS

All pregnant patients with hypertension delivered during a 5-year period at three centers were identified retrospectively. Patients with gestational hypertension, pre-eclampsia, diabetes mellitus, fetal anomalies and absence of a sonographic examination within 3 weeks of delivery were excluded. Likelihood ratio (LR) and guidelines established by the Evidence-Based Medicine Working Group were used to determine whether sonographic EFW is a reliable diagnostic test to detect IUGR.

RESULTS

At the three centers, there were 264 patients with chronic hypertension (122, 77 and 65 at centers I, II and III, respectively). The incidence of IUGR ranged from 13% to 27% but was similar at the three locations (p = 0.064). The LR (with 95% confidence interval (CI)) of detecting IUGR was 4.4 (95% CI 2.5, 7.7), 2.3 (95% CI 1.4, 3.7) and 6.1 (95% CI 2.7, 13.7) at centers I, II and III, respectively. Based on the proportions of abnormal growth, we required 253 and 71 newborns with fetal growth restriction at centers I and II, respectively, to have narrow confidence intervals around the clinically important LR of 10. The extremely low incidence of IUGR at center III (13%) precluded the estimation of required sample size.

CONCLUSION

Use of Evidence-Based Medicine Working Group guidelines indicates that sonographic EFW is slightly to moderately useful in detecting fetal growth restriction in patients with chronic hypertension.

New indications for antepartum testing: making the case for antepartum surveillance or timed delivery for women of advanced maternal age

Maternal age is an independent risk factor for stillbirth; a moderate number of these occur in normally formed babies near term. For a woman 40 years of age or older giving birth, her risk of having a chromosomal anomaly is 1/66. What is not appreciated is that even without medical risk factors, her risk of having a stillbirth after 37 weeks of gestation is 1/116. This article reviews the risks and benefits of the strategy of antepartum testing and timed delivery and discusses the limitations of the available data in this field.

Antenatal testing--benefits and costs

Antenatal testing is a common component of care for the high-risk pregnancy. The goals of antenatal testing include the prevention of stillbirth and the detection of the hypoxic fetus to allow intervention before acidosis and long-term damage. Data regarding the efficacy of antenatal testing are limited by a lack of randomized controlled trials. The majority of available data hinge on observational studies with the inherent potential for bias. There is also a paucity of data comparing the various testing modalities and addressing the issue of the optimal timing of initiation of testing. As well, data are limited regarding the various conditions most likely to benefit from testing and the frequency with which testing should be performed. The issue of cost relating to antenatal testing is an important one. Central to the issue of estimating cost is an understanding of the efficacy of the test. Given our current limitations, we have significant difficulty accurately estimating the cost of antenatal testing; however, rough estimates of cost are made.

Neonatal morbidity and mortality after elective cesarean delivery

This article explores the effects of elective cesarean delivery (ECD) at term on neonatal morbidity and mortality. Available data have limitations, and do not provide conclusive evidence regarding the safety of planned ECD versus planned vaginal delivery. Some data suggest an association between ECD and increased neonatal respiratory morbidity and lacerations, and possibly decreased central and peripheral nervous system injury. Potentially increased risks of neonatal mortality with ECD at term may be counterbalanced by risks for fetal demise in ongoing pregnancies. Patients and physicians considering ECD should review competing risks and benefits; further research is needed to inform these discussions.

Etiology and prevention of stillbirth

OBJECTIVE

This is a systematic review of the literature on the causes of stillbirth and clinical opinion regarding strategies for its prevention.

STUDY DESIGN

We reviewed the causes of stillbirth by performing a Medline search limited to articles in English published in core clinical journals from January 1, 1995, to January 1, 2005. Articles before this date were included if they added historical information relevant to the topic. A total of 1445 articles obtained, 113 were the basis of this review and chosen based on the criterion that stillbirth or fetal death was central to the article.

RESULTS

Fifteen risk factors for stillbirths were identified and the prevalence of these conditions and associated risks are presented The most prevalent risk factors for stillbirth are prepregnancy obesity, socioeconomic factors, and advanced maternal age. Biologic markers associated with increased stillbirth risk are also reviewed, and strategies for its prevention identified.

CONCLUSION

Identification of risk factors for stillbirth assists the clinician in performing a risk assessment for each patient. Unexplained stillbirths and stillbirths related to growth restriction are the 2 categories of death that contribute the most to late fetal losses. Late pregnancy is associated with an increasing risk of stillbirth, and clinicians should have a low threshold to evaluate fetal growth. The value of antepartum testing is related to the underlying risk of stillbirth and, although the strategy of antepartum testing in patients with increased risk will decrease the risk of late fetal loss, it is of necessity associated with higher intervention rates.

What antepartum fetal test should guide the timing of delivery of the preterm growth-restricted fetus? A decision-analysis

OBJECTIVE

The purpose of this study was to use a decision-analytic approach to explore the best strategy for the timing of the delivery of preterm intrauterine growth-restricted fetuses.

STUDY DESIGN

We constructed a decision-analysis model that compared 4 antenatal fetal testing strategies The fetal/neonatal states that were compared included live in utero pregnancy; fetal death; neonatal death; disabled neonate, and healthy neonate. Probability estimates for these states and sensitivity and specificity for Doppler velocimetry and biophysical profile were derived from literature review. Sensitivity analyses were performed on the baseline assumptions.

RESULTS

Under the baseline assumptions, biophysical profile was the best test to guide decisions on delivery. Sensitivity analyses revealed the model to be sensitive only to the specificity of a biophysical profile <82%.

CONCLUSION

Compared with the other options, biophysical profile was the best strategy to guide physicians on the timing of the delivery of the preterm growth-restricted fetus.

Should Older Women Have Antepartum Testing to Prevent Unexplained Stillbirth?

OBJECTIVE

Older women are at an increased risk for unexplained stillbirth late in pregnancy. The purpose of this study was to compare 3 strategies for the prevention of unexplained fetal death in women aged 35 years and older. We compared usual care (no antepartum testing or induction before 41 weeks), weekly testing at 37 weeks with induction after a positive test, and no testing with induction at 41 weeks.

METHOD

We used a Markov model to quantify the risks and benefits of each strategy in terms of the number of antepartum tests, inductions, and additional cesarean deliveries per fetal death averted. Probability data used in the model were derived from obstetrical databases and the literature.

RESULTS

Without a strategy of antepartum surveillance between 37 and 41 weeks, women aged 35 years and older would experience 5.2 unexplained fetal deaths per 1,000 pregnancies. For nulliparous women 35 and older, weekly antepartum testing initiated at 37 weeks would avert 3.9 fetal deaths per 1,000 pregnancies but would require 863 antepartum tests, 71 inductions, and 14 additional cesarean deliveries per fetal death averted. A strategy of no testing but induction at 41 weeks would avert 0.9 fetal deaths per 1,000 pregnancies and require 469 inductions and 219 additional cesareans per fetal death averted.

CONCLUSION

A strategy of antepartum testing in older women would reduce the number of unexplained stillbirths at term and would result in fewer inductions and cesareans per fetal death averted than a strategy of no antepartum testing but induction at 41 weeks.