Maternal Position Research Articles

Factors Affecting Maternal Perception of Fetal Movement

Maternal perception of fetal movement is an important screening method for fetal well-being, as decreased fetal movement is associated with a range of pregnancy pathologies and poor pregnancy outcomes. An understanding of factors that may affect perception could help clinicians to determine the importance of maternal reports of decreased fetal movement. This review considers factors that may affect maternal perception of fetal movement and the sensitivity of maternal perception of fetal movements in comparison with ultrasound and other objective methods of movement detection. There is conflicting evidence on whether parity, gestational age, overweight and obesity, and placental location affect perception. This may be related to the small sample sizes of available studies and lack of consistent definitions of factors that may affect the ability of mothers to perceive movement. There is some evidence that psychological factors and duration of fetal movement may affect perception, and that strong movements and those including trunk movement are more likely to be perceived. The proportion of fetal breathing movements that mothers perceive has not been investigated. Research is also lacking as to whether there needs to be contact of fetal part(s) with maternal structures for movement to be perceived, and whether fetal position, amniotic fluid volume, maternal position, sedatives, or other drugs affect movement perception.

Book Reviews

Written by Helen Churchill, a Principal Lecturer in Sociology, and the obstetrician Wendy Savage, a veteran campaigner for normal birth, this slim volume is subtitled A Handbook for Women who want a Natural Birth, and is a companion piece to the authors' other handbook, Vaginal Birth after Caesarean. It is targeted principally at pregnant women who face the prospect of a caesarean, and is intended to give them information on which to base decisions about their care. As such, its style is open and easy-to-read. Numbered references are given so the text is not interrupted. There are a few line drawings to illustrate fetal and maternal positions.

Transvaginal ultrasound measurement of cervical length in the supine and upright positions versus Bishop score in predicting successful induction of labor at term

To examine the predictive value of cervical length as measured by transvaginal sonography (TVS) in supine and upright maternal positions for the mode of delivery and induction-to-delivery interval after induction of labor at term, and to compare these measurements with the Bishop score and its predictive value. TVS for cervical length measurement in the supine and upright positions and digital examination of the cervix were performed in 68 nulliparous and 34 parous women before induction of labor at term. In assessing the predictive value of the Bishop score and TVS parameters for a vaginal delivery after labor induction only nulliparous women were included in the analysis, since all the parous women delivered vaginally. Both nulliparous and parous women were included in the analysis of the induction-to-delivery interval. The method of labor induction, oxytocin or prostaglandin, was determined on the basis of the pre-induction Bishop score. Logistic regression analysis showed in nulliparous women that only the cervical length measured in the upright position was a significant predictor of the need for Cesarean section (odds ratio 1.14; 95% CI, 1.02-1.27). The areas under the receiver-operating characteristics curve in predicting the need for Cesarean section because of failure to progress were higher for the cervical length, both in supine and upright positions, than for the Bishop score (0.66, 0.68 and 0.46, respectively). Only the Bishop score correlated significantly with the induction-to-delivery interval in both nulliparous and parous women. However, this may have been due to a selection bias, as no significant correlation with Bishop score was found when the oxytocin and prostaglandin induction-to-delivery intervals were analyzed separately. Our results suggest that maternal postural change might improve the accuracy of sonographically-measured cervical length for predicting a vaginal delivery after induction of labor at term. However, our results need to be confirmed in a larger and more homogeneous population.

Maternal position at birth and the newborn Apgar score: cross-sectional study

This is a study of quantitative nature with the aim of establishing the relationship between maternal position in the second period of labor and the condition of the newborn, infant as assessed by Apgar index. A descriptive cross-sectional study was designed, with an analysis of 8,538 live-birth deliveries occurring between 1996 and 2005 at a maternity school in southern Brazil. The analysis included data on all vaginal deliveries with the woman in a vertical (squatting) or horizontal (supine or semi-sitting) position, together with data on their unborn children and their rates of Apgar. There were 5,002 (58.6%) deliveries in the upright position, and 3,536 (41.4%) in the horizontal position. The mean Apgar rate at 1 minute was 8.11 for deliveries in the vertical position, and for the horizontal position it was 8.04 (p=0.009). For the maternal age 15 of 20 years, the mean Apgar rate in the first minute was higher in the vertical deliveries (p

Amino Acid Composition in Fillets of Mirror Crossbreds Common Carp (Cyprinus carpio, Linnaeus 1758)

The aim of the study was to determine the amino acid composition in fillet proteins of newly bred mirror carp lines. In the experiments, the Hungarian mirror carp (M2) were used at the maternal position. These were crossed with male carp of other breeds (top crossing). They included the Hungarian mirror carp (M2) for the production of a pure line, the Hungarian mirror line (L15), the Israeli breed (DOR70) and the Northern mirror carp (M72). The scaly hybrid of the Ropsha (ROP) and the Tataj (TAT) carp was used as a control. In view of the genetic specification of the carp groups monitored, numerous differences (P < 0.01 and P < 0.05) in the composition of specific amino acids (EAA: Val, Leu, Lys, Arg, Met; NEAA: Asp, Glu, Tyr) and their total amounts (EAAsum, NEAAsum) were found between the scaly control (ROP × TAT) and the pure line M2. Higher amino acid values were found in control hybrids. Compositions of amino acids in fillet muscle tissue of experimental mirror carp (M2 × L15, M2 × DOR70) were practically identical. Compared to the controls (ROP × TAT), these carp groups contained less (P < 0.01) Leu, Lys, Arg and Glu. A composition of amino acids statistically comparable with the controls (ROP × TAT) was found only in the M2 × M72 hybrid with the exception of Glu, which was found in smaller quantities in this hybrid (P < 0.01). In terms of sex differences, the greatest amounts of amino acids were found in fillets of male ROP × TAT controls, the amino acid compositions in male and female mirror carp were practically the same. In this type of evaluation, i.e. regarding amino acid composition, the only carp comparable with the ROP × TAT control is the M2 × M72 hybrid.

Second-Stage Labor Care

Substantial scientific evidence supports spontaneous maternal bearing down for its associated maternal and fetal physiologic benefits. Imposing specific directions for Valsalva pushing does not result in optimal outcomes but continues to be widely used, particularly when labor progress is less than optimal. However, there are numerous evidence-based approaches that can be used to avoid reverting to directed, prolonged Valsalva bearing down. Nursing care challenges may be encountered when using physiologic approaches; therefore, strategies are detailed to alleviate a variety of problems including ways to promote physiological descent and effectively support women's spontaneous efforts. For example, maternal postural interventions are suggested for asynclitic and occiput posterior fetal positions. When fetal heart rate abnormalities present and the fetus may be compromised, modifications to spontaneous bearing down are suggested as alternatives to longer and stronger Valsalva pushing, such as encouraging the women to use short pushes or breath through contractions until the fetus recovers. Open knee-chest maternal positioning can help to diminish a premature urge to push, while the closed knee-chest position may be more useful if cervical edema occurs. Even with clinical challenges, evidence-based care can help achieve the improved outcomes documented from women's spontaneous bearing-down efforts during the second stage.

Fetal Pulse Oximetry During Labor: Theory, Clinical Use and the Future

Fetal pulse oximetry (FPO) has evolved through various phases of technical development and calibration. Clinical studies have addressed the issue of determining threshold action values and how well the technology is accepted by childbearing women and their caregivers. This article considers a variety of situations and factors that commonly occur during labor and that may influence fetal oximetry values. These include uterine contractions, supplemental oxygen and intravenous fluids administered to the mother, maternal position and epidural analgesia. The five randomized, controlled trials that compared the use of FPO in addition to fetal heart-rate monitoring with fetal heart-rate monitoring alone, have been systematically reviewed and subjected to meta-analysis where appropriate. Current clinical practice guidelines do not support the routine use of FPO; however, the recent emergence of robust multiwavelength oximeters may, in the future, offer further clinical applications for FPO.

Socio‐economic inequality in preterm birth: a comparative study of the Nordic countries from 1981 to 2000

During the 1980s and 1990s, there were large social and structural changes within the Nordic countries. Here we examine time changes in risks of preterm birth by maternal educational attainment in Denmark, Finland, Norway and Sweden. Information on gestational age and maternal socio-economic position was obtained from the NorCHASE database, which includes comparable population-based register data of births from Denmark, Finland, Sweden and Norway from 1981 to 2000. The risks of very preterm birth (<32 gestational weeks) and moderately preterm birth (32-36 gestational weeks) were calculated by maternal educational attainment and analysed in 5-year intervals from 1981 to 2000. Compared with mothers with >12 years of education, mothers with <10 years of education had similarly increased risks of very, and to a lesser extent moderately, preterm birth in all four countries. The educational gradient increased slightly over time in very preterm births in Denmark, while there was a slight narrowing of the gap in Sweden. In moderately preterm births, the educational inequality gap was constant over the study period in Denmark, Norway and Sweden, but narrowed in Finland. The educational gradient in preterm birth remained broadly stable from 1981 to 2000 in all four countries. Consequently, the socio-economic inequalities in preterm birth were not strongly influenced by structural changes during the period.

Sociodemographic Correlates of the Increasing Trend in Prevalence of Gestational Diabetes Mellitus in a Large Population of Women Between 1995 and 2005

OBJECTIVE—Gestational diabetes mellitus (GDM) is an increasingly prevalent risk factor for the development of type 2 diabetes in the mother and is responsible for morbidity in the child. To better identify women at risk of developing GDM we examined sociodemographic correlates and changes in the prevalence of GDM among all births between 1995 and 2005 in Australia's largest state.RESEARCH DESIGN AND METHODS—A computerized database of all births (n = 956,738) between 1995 and 2005 in New South Wales, Australia, was used in a multivariate logistic regression that examined the association between sociodemographic characteristics and the occurrence of GDM.RESULTS—Between 1995 and 2005, the prevalence of GDM increased by 45%, from 3.0 to 4.4%. Women born in South Asia had the highest adjusted odds ratio (OR) of any region (4.33 [95% CI 4.12–4.55]) relative to women born in Australia. Women living in the three lowest socioeconomic quartiles had higher adjusted ORs for GDM relative to women in the highest quartile (1.54 [1.50–1.59], 1.74 [1.69–1.8], and 1.65 [1.60–1.70] for decreasing socioeconomic status quartiles). Increasing age was strongly associated with GDM, with women aged >40 years having an adjusted OR of 6.13 (95% CI 5.79–6.49) relative to women in their early 20s. Parity was associated with a small reduced risk. There was no association between smoking and GDM.CONCLUSIONS—Maternal age, socioeconomic position, and ethnicity are important correlates of GDM. Future culturally specific interventions should target prevention of GDM in these high-risk groups.

Emergency Cesarean delivery for umbilical cord prolapse: the head-down, knee-chest prone position for spinal anesthesia

Umbilical cord prolapse in a parturient is an emergency, where the need for immediate fetal delivery may conflict with maternal anesthetic risk factors. We describe the anesthetic management of a parturient who was rushed to the operating room, in the knee-chest prone position, because of cord prolapse with variable decelerations of fetal heart rate. A 28-yr-old multiparous patient presented at 37 weeks gestation. Her co-morbidities included morbid obesity and asthma. She had a Mallampati class IV airway. She required emergency Cesarean delivery, in view of umbilical cord prolapse, with evidence of fetal compromise. In light of the airway concerns, the urgency to proceed with delivery, and the presence of a palpable umbilical cord pulse in this position, we performed a spinal anesthetic in the knee-chest prone position, and immediately thereafter turned the patient supine, with lateral uterine displacement. Fetal heart rate was monitored throughout the procedure. The spinal anesthetic required less than five minutes to perform, from the time of skin preparation, until readiness for surgery. The subsequent surgical and anesthetic course was unremarkable. Performing spinal anesthesia in the knee-chest prone position served as an innovative solution for emergency Cesarean delivery in this case. Both the head-down lateral, and the head-down knee-chest prone positions, are compatible with spinal anesthesia, and the maternal position that achieves relief of cord compression, determined by the presence of a palpable umbilical cord pulse, may be the most important factor to determine the optimal approach to spinal anesthesia.

Risk of low Apgar score and socioeconomic position: a study of Swedish male births

AimThe aim of this study was to investigate the association between maternal socioeconomic position and a persistent low Apgar score (a score of < 7 at 1 and 5 min following birth).MethodsThe research is based on a population cohort study of 183 637 males born in Sweden between 1973 and 1976. Data from the Medical Birth Register were linked to Population and Housing Censuses.ResultsThere was evidence that mothers working in non-manual (Odds ratio (OR) 0.83 (0.72–0.97)) and self-employed (OR 0.64 (0.44–0.93)) occupations were less likely to have an infant with a low Apgar score, compared to manual workers. There was evidence that the risk of a low Apgar score decreased as the mother's level of education increased, if the infant was born by instrumental (OR 0.86 (0.74–0.99)) or caesarean section (OR 0.80 (0.68–0.93)) delivery, but not by unassisted vaginal delivery (OR 1.01 (0.92–1.10)).ConclusionThere was a lower risk of poor birth condition in male infants born to more educated and non-manual/self-employed mothers. These differences may contribute to our understanding of socioeconomic differences in infant health and development although the results may not be applicable due to changes over the last 30 years.

The triad in mind: An exploration of what is needed by the learning support assistant to facilitate integration of the child with special educational needs into mainstream education

This paper explores what the learning support assistant needs to help integrate children with educational or behavioural difficulties into mainstream education. Although focussed on one role, the paper is relevant to a wider context and draws upon the author's experience of infant observation in relation to the educational workplace. The paper reflects upon the different roles that workers take up within institutions and how these can be seen to form part of a triad including the maternal, paternal and infant positions. The author suggests that the learning support assistant (and other comparable roles) takes on the maternal role. The paper reflects upon the supposition that mothers function at their best when their own anxieties and fears are contained by the paternal function. Similarly, assistants are only able to contain and support the child when they themselves feel sufficiently supported. The assistant gains from an awareness of paternal and maternal functioning and projective processes. When levels of support are sufficient, the assistant can engage in triadic thinking, hold the link between organisation, child, and individual worker, and function as a container.

ISUOG consensus statement: what constitutes a fetal echocardiogram?

In 2006 the International Society of Ultrasound in Obstetrics and Gynecology (ISUOG) published practice guidelines for the sonographic screening of congenital heart disease (CHD) during the second trimester of pregnancy1. This document described two levels for screening low-risk fetuses for heart anomalies. Firstly, a ‘basic’ scan should be performed by analyzing a four-chamber view of the fetal heart. Secondly, an ‘extended-basic’ scan further examines the size and relationships of both arterial outflow tracts. The term ‘fetal echocardiogram’ was also mentioned as a more detailed sonographic evaluation to be performed by specialists in the prenatal diagnosis of CHD. Although common indications and imaging techniques were briefly discussed, it was thought important to further explain how this advanced diagnostic procedure differs from the basic and extended-basic cardiac screening examinations. A Fetal Echocardiography Task Force was subsequently asked to develop a standard description of ‘what constitutes a fetal echocardiogram’. Our original goal was to develop guidelines for a detailed examination of the fetal heart that were based on the literature and a consensus opinion of an expert panel. However, we soon realized that this project was quite different from developing minimum practice guidelines for fetal cardiac screening. There are several imaging modalities that can be used to evaluate fetal heart anomalies, ranging from M-mode techniques and color Doppler sonography to the use of four-dimensional (4D) ultrasonography with spatiotemporal image correlation (STIC). Consequently, our original efforts to develop a minimum practice guideline for fetal echocardiography evolved into a consensus statement that covers the following topics:

Researching labour and birth events using health information records: methodological challenges

Objectives as little has been published about the particular challenges of researching labour and birth events using health information records (HIRs), this study aimed to describe the methodological and quality assurance (QA) issues encountered in reviewing such records for a study of health and recovery after operative birth, and to report on how these issues were tackled. Design and setting retrospective review of HIRs, recording details of the labour and birth events of 394 women for 630 confinements at 32 hospitals, chiefly situated in the State of Victoria, Australia. Participants three hundred and ninety-four women, a subset of a cohort of 534 women participating in the Health and Recovery after Operative Birth Project, who gave consent to review of their HIRs. Methods a data abstraction form (DAF) and comprehensive accompanying study manual were designed, with the form's layout based on the HIR used by the hospital where the majority of confinements occurred. Amendments were made following piloting of the DAF. Three data abstractors were carefully trained for the task of reviewing records, and issues were dealt with as they arose at fortnightly meetings. Double data abstraction (cross-coding) exercises were conducted three times during the project and reported on for QA purposes. Findings a number of limitations were found with labour and birth event data recorded in the HIRs. For example, maternal position in active second stage labour could not be established for 65% of births, documentation of onset of second stage was not accompanied by definitive evidence for second stage onset in 23.9% of cases, and maternal position at birth was missing in 26.4% of cases. Other relevant variables also proved problematic. For example, infant head circumference was not documented for 24.4% of births, and 52.9% of records did not document maternal height. Time and effort put into data abstractor training, and careful design and piloting of the DAF enabled both the form and data abstraction methods to be adapted following recognition of some of the limitations identified with the records, and also allowed subsequent analytic possibilities to be maximised. Cross-coding exercises also increased data abstractor reliability. Key conclusions and implications for practice the likelihood of obtaining reliable data from HIRs is increased by a keen awareness of the challenges presented by the records themselves, careful training of staff, careful DAF design which allows for documentation of problems, conducting QA checks such as cross-coding exercises, and cautious reporting of findings with appropriate recognition of inherent limitations of the method.

Neuraxial techniques for labor analgesia should be placed in the lateral position

Many consider spinal and epidural insertion to be an art rather than a science, and believe there are no scientific reasons to favor one technique over another. Maternal position is a case in point, where the mother is commonly placed sitting with the belief that evidence to support a particular maternal position is lacking. However, the scientific literature demonstrates clear advantages of the lateral position. Its use optimizes the overall experience and outcome for all three participants: mother, fetus and anesthesiologist.

Optimal positions for the release of primitive neonatal reflexes stimulating breastfeeding

Background Despite widespread skills-teaching, 37% of UK mothers initiating breastfeeding stop by six weeks suggesting a need to reappraise current support strategies. Rooting, sucking and swallowing have been studied extensively but little is known about the role other primitive neonatal reflexes (PNRs) might play to support breastfeeding. Aims To describe and compare PNRs observed during feeding, investigating whether certain feeding behaviours and positions, collectively termed Biological Nurturing, (BN) are associated with the release of those reflexes pivotal in establishing successful feeding. Method 40 breastfed healthy term mother/baby pairs were recruited using quota sampling to stratify term gestational age. Feeding sessions were videotaped in the first postnatal month, either in hospital or at home. Findings 20 PNRs were validated and classified into 4 types (endogenous, motor, rhythmic and anti-gravity) and 2 functional clusters (finding/latching, milk transfer) either stimulating or hindering feeding. Significantly more PNRs were observed as stimulants in semi-reclined postures (BN) than when mothers were upright or side-lying ( p = < 0.0005). Discussion This study is the first to describe a range of semi-reclined maternal postures interacting with neonatal positions, releasing maternal instinctual behaviours and PNRs stimulating breastfeeding. Traditionally the human neonate has been considered a dorsal feeder with pressure needed along the baby's back. Compelling visual data here illustrate that the newborn is an abdominal feeder and, like some other animals, displays anti-gravity reflexes aiding latch. Findings suggest that breastfeeding initiation is innate for both mother and baby, not learned, thus challenging the routine skills-teaching currently central to breastfeeding support.

Avoiding over diagnosis of shoulder dystocia

SummaryIn this study, we aimed to distinguish true shoulder dystocia from mere difficulty with delivery of the shoulder, by investigating the risk factors that lead to shoulder dystocia. Shoulder dystocia is a bony problem which occurs when either the anterior or, less commonly, the posterior fetal shoulder impacts on the maternal symphysis pubis or sacral promontory. Failure to apply the Royal College of Obstetricians and Gynaecologists (RCOG) clinical diagnostic criteria for shoulder dystocia has made it susceptible to over-diagnosis due to inclusion of all difficult shoulder deliveries, including those related to an inappropriate maternal position. This was a retrospective analysis of risk factors associated with 56 cases of shoulder dystocia which occurred in West Middlesex University Hospital between 2003 and 2004. The cases were analysed in two categories, good outcome and poor outcome, and compared with each other. The poor outcome had represented true shoulder dystocia. The incidence of shoulder dystocia increased from 0.94% in 2003 to 1.37% in 2004. However, the incidence of those with a poor outcome decreased from 45.4% of the whole shoulder dystocia group in 2003, to 17.6% in 2004 (p = 0.03). There were no clear diagnostic criteria documented in the notes for the condition other than the birth attendants' opinion and the turtle sign. This may either reflect over-diagnosis from increased awareness or possibly improvement in the outcome due to training and education. Interestingly, at least four risk factors were identified in each of the cases with poor outcome. A registrar conducting the delivery, forceps delivery for delayed second stage and the turtle sign were significantly common findings among the true shoulder dystocia group. Multiple risk factors can be a good predictor for the occurrence of shoulder dystocia. Applying the RCOG diagnostic criteria for shoulder dystocia may lead to improvement in diagnosis and therefore a better understanding of the risk factors and future management of shoulder dystocia.

Prepregnancy cardiovascular risk factors as predictors of pre-eclampsia: population based cohort study

Objective To examine the effect of cardiovascular risk factors before pregnancy on risk of pre-eclampsia.Design Population based prospective study.Setting Linkage between a Norwegian population based study (Nord-Trøndelag health study, HUNT-2)...

Hands and knees posture in late pregnancy or labour for fetal malposition (lateral or posterior)

Lateral and posterior position of the baby's head (the back of the baby's head facing to the mother's side or back) may be associated with more painful, prolonged or obstructed labour and difficult delivery. It is possible that certain positions adopted by the mother may influence the baby's position. To assess the effects of adopting a hands and knees maternal posture in late pregnancy or during labour when the presenting part of the fetus is in a lateral or posterior position compared with no intervention. We searched the Cochrane Pregnancy and Childbirth Group's Trials Register (July 2007) and the Cochrane Central Register of Controlled Trials (The Cochrane Library 2007, Issue 2). Randomised trials of hands and knees maternal posture compared to other postures or controls. Two review authors assessed trial eligibility and quality. Three trials (2794 women) were included. In one trial (100 women), four different postures (four groups of 20 women) were combined for the comparison with the control group of 20 women. Lateral or posterior position of the presenting part of the fetus was less likely to persist following 10 minutes in the hands and knees position compared to a sitting position (one trial, 100 women, relative risk (RR) 0.26, 95% confidence interval (CI) 0.18 to 0.38). In a second trial (2547 women), advice to assume the hands and knees posture for 10 minutes twice daily in the last weeks of pregnancy had no effect on the baby's position at delivery or any of the other pregnancy outcomes measured. The third trial studied the use of hands and knees position in labour and involved 147 labouring women at 37 or more weeks gestation. Occipito-posterior position of the baby was confirmed by ultrasound. Seventy women, who were randomised in the intervention group, assumed hands and knees positioning for a period of at least 30 minutes, compared to 77 women in the control group who did not assume hands and knees positioning in labour. The reduction in occipito-posterior or -transverse positions at delivery and operative deliveries were not statistically significant. There was a significant reduction in back pain. Use of hands and knees position for 10 minutes twice daily to correct occipito-posterior position of the fetus in late pregnancy cannot be recommended as an intervention. This is not to suggest that women should not adopt this position if they find it comfortable. The use of position in labour was associated with reduced backache. Further trials are needed to assess the effects on other labour outcomes.

Risk factors for anal sphincter tears: the importance of maternal position at birth

To assess the role of birth position in the occurrence of anal sphincter tears (AST). Observational cohort study. South Hospital in Stockholm, a teaching hospital with around 5700 births per year. Among all 19,151 women who gave birth at the South Hospital during the study period 2002-05, 12,782 women met the inclusion criteria of noninstrumental, vaginal deliveries. Data on birth position and other obstetric factors were analysed in relation to occurrence of AST. Third- and fourth-degree AST. AST occurred in 449 women (3.5%). The trauma was more frequent in primiparous (5.8%) than in multiparous women (1.7%). The highest proportion of AST was found among women who gave birth in lithotomy position (6.9%), followed by squatting position (6.4%). Logistic regression analyses showed that lithotomy (adjusted OR 2.02, 95% CI 1.58-2.59) and squatting positions (adjusted OR 2.05, 95% CI 1.09-3.82) were associated with a significantly increased risk for AST. Other major risk factors for anal sphincter trauma were primiparity (adjusted OR 3.29, 95% CI 2.55-4.25), prolonged second stage of labour >1 hour (adjusted OR 1.52, 95% CI 1.11-2.10), infant birthweight more than 4 kg (adjusted OR 2.12, 95% CI 1.64-2.72) and large infant head circumference (adjusted OR 1.57, 95% CI 1.23-1.99). Lithotomy and squatting position at birth were associated with an increased risk for AST also after control for other risk factors.