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Electronic Delivery Book: Structured Database Enables Analysis of Perinatal Risk Factors
Abstract
The Electronic Delivery Book (EDB), an electronic information system, was developed in cooperation with obstetricians, midwives, and neonatologists from the University Hospital in Brno. The main aim was to create structured electronic documentation of selected delivery-related parameters based on the existing paper-based documentation. The system contains information from the different stages of delivery: parameters of the pregnancy, medications/interventions during the birth, outcome measures for the newborn(s), and primary attributes from neonatology. The EDB also allows creating overviews and basic statistics for everyday clinical needs and offers structured data for retrospective as well as prospective studies. One of the first results based on data collected using the EDB was the analysis aimed at identification of potential risk factors for low umbilical cord artery pH in term, singleton pregnancies. The data selected from EDB represents a basis for the retrospective case-control study. Cases were deliveries characterized by umbilical cord artery pH ≤7.05, controls were with no sign of hypoxia. In the database of 10637 deliveries, collected between 2014 and 2015 at the University Hospital in Brno, we identified 99 cases. Univariate analysis of clinical features was performed. The following risk factors were associated with low pH: the length of the first stage (odds ratio (OR) 1.40; 95% CI 1.04–1.89) and the length of the second stage of labor (OR 2.86; 1.70–4.81), primipara (OR 2.99; 1.90–4.71) and meconium stained fluid (OR 1.60; 1.07–2.38).
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Background:
The fetal heart rate (FHR) is commonly monitored during labor to detect early fetal acidosis. FHR variability is traditionally investigated using Fourier transform, often with adult predefined frequency band powers and the corresponding LF/HF ratio. However, fetal conditions differ from adults and modify spectrum repartition along frequencies.
Aims:
This study questions the arbitrariness definition and relevance of the frequency band splitting procedure, and thus of the calculation of the underlying LF/HF ratio, as efficient tools for characterizing intrapartum FHR variability.
Study design:
The last 30 minutes before delivery of the intrapartum FHR were analyzed.
Subjects:
Case-control study. A total of 45 singletons divided into two groups based on umbilical cord arterial pH: the Index group with pH ≤ 7.05 (n = 15) and Control group with pH > 7.05 (n = 30).
Outcome measures:
Frequency band-based LF/HF ratio and Hurst parameter.
Results:
This study shows that the intrapartum FHR is characterized by fractal temporal dynamics and promotes the Hurst parameter as a potential marker of fetal acidosis. This parameter preserves the intuition of a power frequency balance, while avoiding the frequency band splitting procedure and thus the arbitrary choice of a frequency separating bands. The study also shows that extending the frequency range covered by the adult-based bands to higher and lower frequencies permits the Hurst parameter to achieve better performance for identifying fetal acidosis.
Conclusions:
The Hurst parameter provides a robust and versatile tool for quantifying FHR variability, yields better acidosis detection performance compared to the LF/HF ratio, and avoids arbitrariness in spectral band splitting and definitions.
The World Health Organization (WHO) estimates that 4 million children are born with asphyxia every year, of which 1 million die and an equal number survive with severe neurologic sequelae. The purpose of this study was to identify the risk factors of birth asphyxia and the hospital outcome of affected neonates.
This study was a prospective case-control study on term neonates in a tertiary hospital in Yaounde, with an Apgar score of < 7 at the 5th minute as the case group, that were matched with neonates with an Apgar score of ≥ 7 at the 5th minute as control group. Statistical analysis of relevant variables of the mother and neonates was carried out to determine the significant risk factors.
The prevalence of neonatal asphyxia was 80.5 per 1000 live births. Statistically significant risk factors were the single matrimonial status, place of antenatal visits, malaria, pre-eclampsia/eclampsia, prolonged labor, arrest of labour, prolonged rupture of membranes, and non-cephalic presentation. Hospital mortality was 6.7%, that 12.2% of them had neurologic deficits and/or abnormal transfontanellar ultrasound/electroencephalogram on discharge, and 81.1% had a satisfactory outcome.
The incidence of birth asphyxia in this study was 80.5% per1000 live birth with a mortality of 6.7%. Antepartum risk factors were: place of antenatal visit, malaria during pregnancy, and preeclampsia/eclampsia. Whereas prolonged labor, stationary labor, and term prolonged rupture of membranes were intrapartum risk faktors. Preventive measures during prenatal visits through informing and communicating with pregnant women should be reinforced.
Background:
Cardiotocography (CTG) is a monitoring of fetal heart rate and uterine contractions. Since 1960 it is routinely used by obstetricians to assess fetal well-being. Many attempts to introduce methods of automatic signal processing and evaluation have appeared during the last 20 years, however still no significant progress similar to that in the domain of adult heart rate variability, where open access databases are available (e.g. MIT-BIH), is visible. Based on a thorough review of the relevant publications, presented in this paper, the shortcomings of the current state are obvious. A lack of common ground for clinicians and technicians in the field hinders clinically usable progress. Our open access database of digital intrapartum cardiotocographic recordings aims to change that.
Description:
The intrapartum CTG database consists in total of 552 intrapartum recordings, which were acquired between April 2010 and August 2012 at the obstetrics ward of the University Hospital in Brno, Czech Republic. All recordings were stored in electronic form in the OB TraceVue®;system. The recordings were selected from 9164 intrapartum recordings with clinical as well as technical considerations in mind. All recordings are at most 90 minutes long and start a maximum of 90 minutes before delivery. The time relation of CTG to delivery is known as well as the length of the second stage of labor which does not exceed 30 minutes. The majority of recordings (all but 46 cesarean sections) is - on purpose - from vaginal deliveries. All recordings have available biochemical markers as well as some more general clinical features. Full description of the database and reasoning behind selection of the parameters is presented in the paper.
Conclusion:
A new open-access CTG database is introduced which should give the research community common ground for comparison of results on reasonably large database. We anticipate that after reading the paper, the reader will understand the context of the field from clinical and technical perspectives which will enable him/her to use the database and also understand its limitations.
Objective:
To identify potential risk factors for cesarean delivery following labor induction in multiparous women at term.
Methods:
We conducted a retrospective case-control study. Cases were parous women in whom the induction of labor had resulted in a cesarean delivery. For each case, we used the data of two successful inductions as controls. Successful induction was defined as a vaginal delivery after the induction of labor. The study was limited to term singleton pregnancies with a child in cephalic position.
Results:
Between 1995 and 2010, labor was induced in 2548 parous women, of whom 80 had a cesarean delivery (3%). These 80 cases were compared to the data of 160 parous women with a successful induction of labor. In the multivariate analysis history of preterm delivery (odds ratio (OR) 5.3 (95% CI 1.1 to 25)), maternal height (OR 0.87 (95% CI 0.80 to 0.95)) and dilatation at the start of induction (OR 0.43 (95% CI 0.19 to 0.98)) were associated with failed induction.
Conclusion:
In multiparous women, the risk of cesarean delivery following labor induction increases with previous preterm delivery, short maternal height, and limited dilatation at the start of induction.
Since 1960's obstetricians have been using cardiotocography (CTG) to detect possible ongoing hypoxia of the fetus. CTG consists of fetal heart rate (fHR) and uterine contraction (TOCO) monitoring. The evaluation of the fHR in clinical settings is ruled by FIGO guidelines, which are based on evaluation of macroscopic morphological features derived from the fHR, such as baseline variability. Although upgrades were proposed to the guidelines - none of them is taking into account results achieved by the adult heart rate variability research. In this work, almost complete set of features previously used for fHR description is investigated and the features are assessed based on their statistical significance in the task of distinguishing the records into three FIGO classes. Inter-correlation of the features is also discussed. We assess the features on a large data set and use expert signal evaluation instead of pH values with the aim to give an overall view of the potential usefulness of the features in the clinical settings. We conclude the paper by presenting the best uncorrected feature subset according to the meta-analysis of three different ranking methods.
The relative risk (RR) and the odds ratio (OR) are the two most widely used measures of association in epidemiology. The direct computation of relative risks is feasible if meaningful prevalences or incidences are available. Cross-sectional data may serve to calculate relative risks from prevalences. Cohort study designs allow for the direct calculation of relative risks from incidences. The situation is more complicated for casecontrol studies. If meaningful prevalences or incidences are not available, the OR provides a valid effect measure: It describes the ratio of disease odds given exposure status, or alternatively the ratio of exposure odds given the disease status. Computationally, both approaches lead to the same result. The OR for a given exposure is routinely obtained within logistic models while controlling for confounders. The availability of this approach in standard statistical software largely explains the popularity of this measure. However, it does not have as intuitive an interpretation as the relative risk. This is where problems start: OR’s are often interpreted as if they were equivalent to relative risks while ignoring their meaning as a ratio of odds. It is for instance common to describe an OR of “2” in terms of a “twofold risk” of developing a disease given exposure. This inaccuracy entails potentially serious problems because the OR always overestimates the RR. This can easily be deduced from the mathematical formulas as depicted in Table 1 because of the way the denominators differ.
The influence of maternal, obstetric and fetal risk factors on the prevalence of birth asphyxia at term in a Swedish urban population.
To investigate risk factors for Apgar score-defined birth asphyxia, birth asphyxia with hypoxic-ischemic encephalopathy and birth asphyxia-related death/disability.
Retrospective case-control study in term neonates with birth asphyxia defined as Apgar score < 7 at 5 min. Cases originating from nonasphyctic causes (e.g. infection, maternal sedation) were excluded. Hypoxic-ischemic encephalopathy was diagnosed according to criteria by Sarnat. Maternal, obstetric and fetal risk factors were registered in 225 cases of birth asphyxia diagnosed in 42 203 live births occurring in the urban Swedish population studied. A matched control group was used for statistical evaluation.
Asphyxia was associated with single civil status, OR = 7.1 (95%CI 2.0, 27.6); intrauterine meconium release, OR = 4.1 (95%CI 1.8, 9.8); operative delivery, OR = 8.7 (95%CI 3.4, 24.6); breech delivery, OR = 20.3 (95%CI 3.0, 416.5); oxytocin augmentation, OR = 2.9 (95%CI 1.4, 6.3); cord complication, OR = 15.8 (95%CI 2.1, 341.5); external compression to assist delivery OR = 6.2 (95%CI 1.3, 45.7); and cardiotocography score, OR = 0.5 (95%CI 0.4, 0.6). Normal fetal heart rate variability, OR = 0.4 (95%CI 0.2, 0.6), repeated late decelerations irrespective of amplitude or repeated variable decelerations, OR = 29.4 (95%CI 5.7, 540.8) or occasional late or variable decelerations, OR = 2.2 (95%CI 1.3, 3.8), and no accelerations, OR = 5.2 (95%CI 2.0, 16.4), were associated with asphyxia. Operative or instrumental delivery was more common in all three asphyxia groups compared with controls. Leanness was a risk factor for asphyxia and for hypoxic-ischemic encephalopathy. Maternal age, smoking and illnesses, time of delivery (day/night, seasonal) and previous caesarean section were not associated with birth asphyxia.
An association between neonatal asphyxia and cardiotocography parameters, intrauterine meconium release, operative delivery, breech delivery, single civil status, oxytocin augmentation, cord complication, external compression to assist delivery and neonatal leanness was found. Abnormal fetal heart rate variability, repeated late decelerations irrespective of amplitude or repeated variable decelerations, occasional late or variable decelerations and no accelerations were associated with asphyxia.
Many perinatal deaths follow birth asphyxia that occurs in newborn babies of women who are referred on developing life-threatening obstetric complications.
To determine the antenatal and intrapartum risk factors for severe birth asphyxia among babies delivered by women admitted as emergency obstetric referrals.
Case-control study.
Mulago hospital, the National Referral Hospital, Kampala, Uganda.
Cases were newborn term babies (and their mothers) with a 5-minute Apgar score 4 or less (birth asphyxia). Controls were term newborn babies with a 5-minute Apgar score more than 4.
Antepartum and intrapartum risk factors among newborn babies (and their mothers) from socio-demographic characteristics, obstetric complications or labour management. The Odds ratios (OR) for various outcomes were calculated using the Statistical Assistance Software (SAS) version 6.2 (Windows), and are presented with their 95% confidence intervals (C1) and p-values.
There was no association between socio-demographic factors and birth asphyxia. Antepartum hospitalization, antepartum or intrapartum anaemia, antepartum hemorrhage and severe pre-eclampsia/eclampsia were significantly associated with birth asphyxia; the respective ORs and 95% C1 were 1.73 (1.09-2.75), 5.65 (3.36-9.50), 2.12 (1.11-4.05) and 10.62 (2.92-38.47). Augmentation of labour with oxytocin, premature rupture of membranes, meconium staining of liquor amnii, vacuum extraction, caesarean section, low birth weight and mal-presentations were significantly associated with birth asphyxia with ORs of 5.76 (2.20-15.05), 2.23 (1.31 -3.37), 6.40 (2.76-14.82), 2.16 (1.28-3.67), 2.36 (1.07-5.20) and 6.32 (3.57-11.20) respectively.
Early recognition of these complications among emergency obstetric referrals, followed by prompt and appropriate management, may reduce the perinatal deaths from birth asphyxia.
There has been an escalation in Caesarean section rates globally. Numerous prenatal factors have been associated with elective and emergency Caesarean section, some of which may be amenable to change.
A population-based cohort of 12,944 singleton, liveborn, term pregnancies were used to investigate risk factors for Caesarean section using multivariable logistic regression modelling. Numerous prenatal factors were investigated for their associations with the following outcomes: first, with Caesarean section (both elective and emergency) compared with vaginal delivery (spontaneous and assisted); second, for their associations with elective Caesarean section compared with attempted vaginal delivery; and finally emergency Caesarean section compared with spontaneous vaginal delivery.
11,791 women had vaginal delivery and 1153 had Caesarean section (685 emergency, 468 elective). Non-cephalic (breech) presentation (all Caesareans odds ratio (OR) 36.6, 95% confidence interval (CI) 26.8-50.0; elective Caesarean OR 86.4, 95% CI 58.5-127.8; emergency Caesarean OR 9.58, 95% CI 6.06-15.1) and previous Caesarean section (all Caesareans OR 27.8, 95% CI 20.9-37.0, elective Caesarean OR 54.4, 95% CI 38.4-77.5; emergency Caesarean OR 13.0, 95% CI 7.76-21.7) were associated in all analyses with an increased risk of Caesarean section. Extremes of neonatal birthweight were associated with an increased risk of Caesarean section (all Caesareans and emergency section) compared with vaginal delivery as was increasing neonatal head circumferences. In all analyses increasing maternal age (OR 1.07 per year, 95 % CI 1.04-1.09; OR 1.04 per year, 95 % CI 1.01-1.08; OR 1.11 per year, 95% CI 1.08-1.15) was independently associated with increased odds of Caesarean section. Increasing parity was associated with a decrease in risk for all Caesareans and emergency section (OR 0.63, 95% CI 0.53-0.75 and OR 0.46, 95% CI 0.33-0.63, respectively), as was the outcome of the last pregnancy being a live child. Increasing gestation was independently associated with a decreased risk of both all Caesareans and elective Caesarean (OR 0.86, 95% CI 0.80-0.93 and OR 0.52, 95% CI 0.46-0.58 respectively), whereas diabetes mellitus was associated with increased risk. These variables were not associated with emergency section. However, epidural use was associated with an increased risk of emergency Caesarean (OR 6.49, 95% CI 4.78-8.82) while being in a preferred labour position decreased the risk (OR 0.59, 95% CI 0.49-0.73).
A careful exploration of risk factors may allow us to identify reasons for the increasing rates of Caesarean section and the marked variation between institutions.
The most common approach to assess fetal well-being during delivery is monitoring of fetal heart rate and uterine contractions-the cardiotocogram (CTG). Nevertheless, 40 years since the introduction of CTG to clinical practice, its evaluation is still challenging with high inter- and intra-observer variability. Therefore the development of more objective methods has become an issue of major importance in the field. Unlike the usually proposed approaches to assign classes for classification methods that rely either on biochemical parameters (e.g. pH value) or a simple aggregation of expert judgment, this work investigates the use of an alternative labeling system using latent class analysis (LCA) along with an ordinal classification scheme. The study is performed on a well-documented open-access database, where nine expert obstetricians provided CTG annotations. The LCA is proposed here to produce more objective class labels while the ordinal classification aims to explore the natural ordering, and representation of increased severity, for obtaining the final results. The results are promising suggesting that more effort should be put into this proposed approach.
To examine the relationship between umbilical cord pH at term and serious neonatal outcomes.
Observational cohort study.
Deliveries within the Oxford Radcliffe Hospital NHS Trust between 1991 and 2009.
In all, 51,519 singleton, term, nonanomalous live neonates with validated umbilical cord arterial pH values.
Absolute risks, relative risks with 95% confidence intervals, and numbers needed to harm were calculated for different levels of arterial pH across the entire range.
Neonatal encephalopathy with seizures and/or death, encephalopathy within 24 hours of birth, 5-minute Apgar scores and neonatal unit admission.
The median arterial pH was 7.22, interquartile range 7.17-7.27. The absolute risk of an adverse neurological outcome was significantly increased below 7.10 (0.36%) and was lowest between 7.26 and 7.30 (0.16%). Even below 7.00, the risk was only 2.95%. However, more than 75% of neonates with neurological outcomes examined, including seizures within 24 hours of birth, had a pH above 7.10. A small increase in risk was evident at higher pH levels.
The threshold pH for adverse neurological outcomes is 7.10 and the 'ideal' cord pH is 7.26-7.30. Above 7.00, however, neonatal acidaemia is weakly associated with adverse outcomes. Most neonates with neurological morbidity have normal cord pH values. Other variables must influence adverse outcomes and account for more of these than acidaemia. A better understanding of these is required before intrapartum fetal monitoring can improve.
The study was conducted to identify medical, obstetrical and social risk factors associated with early preterm births (<32+0 gestational weeks).
The Statewide Perinatal Survey of Bavaria is a collection of perinatal data from all Bavarian maternity units using a uniform numbered questionnaire. Data on 106345 singleton births from the 1994 Survey were analysed using univariate and multivariate logistic regression analysis.
In the multivariate analysis, early preterm birth was associated with premature rupture of the membranes (odds ratio (OR) 1.6, 95% confidence interval (CI) 1.37-1.86), treatment for infertility (OR 1.7, 95% CI 1.19-2.34), previous induced abortion (OR 1.8, 95% CI 1.57-2.13), maternal age >35 years (OR 1.8, 95% CI 1.47-2.16), premature cervical dilatation (OR 2.3, 95% CI 1.86-2.94), a history of stillbirth (OR 3.2, 95% CI 2.13-4.83), a history of preterm birth (OR 3.3, 95% CI 2.45-4.48), maternal age <18 years (OR 3.4, 95% CI 2.03-5.61), malpresentation (OR 3.9, 95% CI 3.10-4.93), preeclampsia (OR 4.0, 95% CI 3.20-4.94), uterine bleeding (OR 5.0, 95% CI 4.08-6.02), preterm labour (OR 7.0, 95% CI 5.94-8.22), and chorioamnionitis (OR 22.3, 95% CI 17.40-28.66).
These data identify a subgroup of women at an increased risk for early preterm birth and may benefit from an intensified prenatal care. Risk factors related to the obstetrical history, genital infections, preeclampsia and maternal age are the most relevant for early preterm birth.
Our goals were to compare duration of labor at term for (1) women with preeclampsia versus normotensive nulliparous women and (2) nulliparous women with preeclampsia who received magnesium for seizure prophylaxis versus those who did not.
We performed a retrospective cohort study of all nulliparous, term vaginal deliveries from 1989 through 1995 at University of California, San Francisco. The perinatal database and medical records were reviewed for information on duration of labor, maternal and labor characteristics, and neonatal outcomes. The chi2 odds ratio, and Student t tests were used to compare categoric and continuous variables between women with preeclampsia and control women and between women with preeclampsia who did and those who did not receive magnesium. Logistic regression was used to evaluate variables predictive of labor duration.
Our study subjects were 4083 normotensive nulliparous women and 154 women with preeclampsia. A sample size calculation revealed that 1764 normotensive control subjects were needed to show a 10% difference in labor duration with 80% power and alpha of 0.05. Among women with preeclampsia, 93 (60%) were treated with magnesium and 61 (40%) were not. More women with preeclampsia than normotensive women had induction of labor and received epidural anesthesia, prostaglandin gel, and oxytocin (P <.003). Total labor duration did not differ between women with preeclampsia and normotensive women (P =.15) or between women with preeclampsia who received magnesium and those who did not (P =.09). In comparison with normotensive women, those with preeclampsia had a higher rate of postpartum hemorrhage (31% vs 22%, P =.005), and the rate was even higher among preeclamptic women treated with magnesium versus those who received no magnesium (34% vs 26%, P =.002). Logistic regression, with prolonged first stage of labor (>12 hours) used as the outcome variable, indicated that epidural anesthesia (odds ratio 2.3, 95% confidence interval 1.9-2. 6), oxytocin (odds ratio 1.8, 95% confidence interval 1.6-2.2), and persistent occipitoposterior presentation (odds ratio 1.6, 95% confidence interval 1.1-2.4) were associated with prolonged labor, whereas preeclampsia (odds ratio 0.9, 95% confidence interval 0.7-1. 1) and treatment with magnesium were not (odds ratio 1.1, 95% confidence interval 0.9-1.4). Induction (odds ratio 0.5, 95% confidence interval 0.4-0.6) and birth weight <2500 g (odds ratio 0. 5, 95% confidence interval 0.4-0.8) were associated with faster labor.
In term nulliparous women, neither preeclampsia nor magnesium prophylaxis affected labor duration.
In recent years odds ratios have become widely used in medical reports—almost certainly some will appear in today's BMJ. There are three reasons for this. Firstly, they provide an estimate (with confidence interval) for the relationship between two binary (“yes or no”) variables. Secondly, they enable us to examine the effects of other variables on that relationship, using logistic regression. Thirdly, they have a special and very convenient interpretation in case-control studies (dealt with in a future note).The odds are a way of representing probability, especially familiar for betting. For example, the odds that a single throw of a die will produce a six are 1 to 5, or 1/5. The odds is the ratio of the probability that the event of interest occurs to the probability that it does not. This is often estimated by the ratio of the number of times that the event of interest occurs to …
We used data on 6,805 live births from the National Maternal and Infant Health Survey to examine the positive association between maternal age and Cesarean delivery.
For parous women, the unadjusted risk ratio [RR] for Cesarean, comparing 35 year olds with 20 year olds, was estimated to be 1.40 [95% confidence limits (CL)=1.18, 1.65]; this association disappeared upon adjustment for obstetrical predictors and other factors (adjusted RR=1.04; 95% CL=0.80, 1.35). In contrast, for nulliparous women, the unadjusted risk ratio was 2.16 (95% CL=1.78, 2.63) and remained substantial upon adjustment (RR=1.74; 95% CL=1.25, 2.43).
These results, along with baseline risk information, suggest that older nulliparous women and their obstetricians should be the target of future efforts to control Cesarean rates.
Nonreassuring fetal heart rate patterns, prolonged labor, meconium-stained fluid, a low 1-minute Apgar score, and mild to moderate acidemia have no predictive value for long-term neurologic injury without signs of encephalopathy and seizures. It is important to provide proper resuscitation, support infants, and allow time for evaluation. We have time and the tools to provide fairly predictive information to the families. It is important to use this knowledge wisely in communicating honestly with families, because difficult decisions undoubtedly will arise.
This paper reviews the research literature on electronic health record (EHR) systems. The aim is to find out (1) how electronic health records are defined, (2) how the structure of these records is described, (3) in what contexts EHRs are used, (4) who has access to EHRs, (5) which data components of the EHRs are used and studied, (6) what is the purpose of research in this field, (7) what methods of data collection have been used in the studies reviewed and (8) what are the results of these studies.
This paper is intended to serve as a comprehensive introduction to the emerging field concerned with the design and use of ontologies. We observe that disparate backgrounds, languages, tools, and techniques are a major barrier to effective communication among people, organisations, and/or software systems. We show how the development and implementation of an explicit account of a shared understanding (i.e. an `ontology') in a given subject area, can improve such communication, which in turn, can give rise to greater reuse and sharing, inter-operability, and more reliable software. After motivating their need, we clarify just what ontologies are and what purposes they serve. We outline a methodology for developing and evaluating ontologies, first discussing informal techniques, concerning such issues as scoping, handling ambiguity, reaching agreement and producing definitions. We then consider the benefits of and describe, a more formal approach. We re-visit the scoping phase, and discuss the role of formal languages and techniques in the specification, implementation and evaluation of ontologies. Finally, we review the state of the art and practice in this emerging field, considering various case studies, software tools for ontology development, key reearch issues and future prospects.
Umair Iqbal, Sehrish Muhammad Saleem, Muhammad Waqas Abid Shaikh, and Nazish Shahid. Risk factors of birth asphyxia
- Shafaq Hafiz Muhammad Aslam
- Rafia Saleem
- Afzal
Explaining the association of maternal age with cesarean delivery for nulliparous and parous women
- Hal Ilana F Gareen
- Sander Morgenstern
- Deidre Spelliscy Greenland
- Gifford