NCBI Bookshelf. A service of the National Library of Medicine, National Institutes of Health.

National Collaborating Centre for Women's and Children's Health (UK). Induction of Labour. London: RCOG Press; 2008 Jul. (NICE Clinical Guidelines, No. 70.)

Cover of Induction of Labour

Induction of Labour.

Show details

Glossary of terms


A step-by-step problem solving procedure designed to guide users through clinical decision pathways.


Artificial rupture of the membranes to initiate or speed up labour.


Pain relief without loss of consciousness.


Before birth.

Apgar score

A scoring system devised by Dr Virginia Apgar (1909–74) based on five criteria (heart rate, respiration, colour, muscle tone and response to stimulation) and used as a marker of a newborn baby’s need for resuscitation at birth. A score of 0, 1 or 2 is awarded for each criterion, with a total score out of ten. The score is assessed at 1 and 5 minutes after birth.

Augmentation of labour

A process where the progress of labour is enhanced by administration of an infusion of oxytocin.

Balloon catheter

A flexible tube with an inflatable balloon at one end. This can be introduced through the cervix and the balloon inflated, holding the catheter in place. Drugs or fluids may then be infused via the catheter.


Influences on a study that can lead to invalid conclusions about a treatment or intervention. Bias occurs as a result of defects in the study design or the way the study is carried out. It can occur at various stages in the research process, for example in the collection, analysis, interpretation, publication or review of research data.

Bishop score

A group of measurements made at internal examination, used to determine whether the cervix is favourable or not. The score is based on the station, dilation, effacement (or length), position and consistency of the cervix. A score of 8 or more generally indicates that the cervix is ripe See cervical ripeness.

Blinding or masking

The practice of keeping the investigators or subjects of a study ignorant of the group to which a subject has been assigned. For example, a clinical trial in which the participating patients or their doctors are unaware of whether they (the patients) are taking the experimental drug or a placebo (dummy treatment). The purpose of ‘blinding’ or ‘masking’ is to protect against bias.

Breech presentation

Initial presentation of the fetal buttocks or feet (‘footling breech’) in the birth canal.

Caesarean section

Operative delivery of the fetus through an abdominal incision.

Cardiotocography (CTG)

A method of monitoring the fetal heart rate (FHR) pattern in relation to the pattern and intensity of uterine contractions. The FHR can be monitored non-invasively using a sensor attached to the woman’s abdomen, or invasively using an electrode attached to the presenting part of the fetus (usually the fetal scalp). The uterine contractions are recorded using an external sensor held in place on the woman’s abdomen. Changes in FHR that suggest fetal compromise may prompt the need for an instrumental or operative birth of the baby. Also referred to as electronic fetal monitoring (EFM).

Case–control study

A study that starts with the identification of a group of individuals sharing the same characteristics (e.g. people with a particular disease) and a suitable comparison (control) group (e.g. people without the disease). All subjects are then assessed with respect to things that happened to them in the past, for example things that might be related to getting the disease under investigation. Such studies are also called retrospective as they look back in time from the outcome to the possible causes.

Case series

Description of several cases of a given disease, usually covering the course of the disease and the response to treatment. There is no comparison (control) group of patients.

Cervical ripeness

The extent to which the cervix has softened and shortened in the early phase of labour. It is assessed using the Bishop score.

Cervical ripening

A prelude to the onset of labour whereby the cervix becomes soft and compliant. This allows its shape to change from being long and closed, to being thinned out (effaced) and starting to open (dilate). It either occurs naturally or as a result of physical or pharmacological interventions.


The neck of the uterus where it joins the vagina.


Inflammation of the fetal membranes caused by infection as a result of, or causing rupture of the membranes. It is associated with preterm birth and potentially serious neonatal morbidity, including congenital pneumonia and brain injury, as well as maternal infection (endometritis).

Clinical audit

A systematic process for setting and monitoring standards of clinical care. Whereas ‘guidelines’ define what the best clinical practice should be, ‘audit’ investigates whether best practice is being carried out. Clinical audit can be described as a cycle or spiral. Within the cycle there are stages that follow a systematic process of establishing best practice, measuring care against specific criteria, taking action to improve care, and monitoring to sustain improvement. The spiral suggests that, as the process continues, each cycle aspires to a higher level of quality.

Clinical effectiveness

The extent to which a specific treatment or intervention, when used under usual or everyday conditions, has a beneficial effect on the course or outcome of disease compared with no treatment or other routine care. (Clinical trials that assess effectiveness are sometimes called management trials.) Clinical ‘effectiveness’ is not the same as efficacy.

Clinical question

A term is sometimes used in guideline development work to refer to the questions about treatment and care that are formulated in order to guide the search for research evidence. When a clinical question is formulated in a precise way, it is called a focused question.

Clinical trial

A research study conducted with patients which tests out a drug or other intervention to assess its effectiveness and safety. Each trial is designed to answer scientific questions and to find better ways to treat individuals with a specific disease. This general term encompasses controlled clinical trials and randomised controlled trials.


A qualified healthcare professional providing patient care, for example doctor, nurse, physiotherapist.


A group of people sharing some common characteristic (e.g. patients with the same disease), followed up in a research study for a specified period of time.

Cohort study

An observational study that takes a group (cohort) of patients and follows their progress over time in order to measure outcomes such as disease or mortality rates and make comparisons according to the treatments or interventions that patients received. Thus within the study group, subgroups of patients are identified (from information collected about patients) and these groups are compared with respect to outcome, for example comparing mortality between one group that received a specific treatment and one group which did not (or between two groups that received different levels of treatment). Cohorts can be assembled in the present and followed into the future (a ‘concurrent’ or ‘prospective’ cohort study) or identified from past records and followed forward from that time up to the present (a ‘historical’ or ‘retrospective’ cohort study). Because patients are not randomly allocated to subgroups, these subgroups may be quite different in their characteristics and some adjustment must be made when analysing the results to ensure that the comparison between groups is as fair as possible.

Confidence interval

A way of expressing the degree of certainty about the findings from a study or group of studies, using statistical techniques. A confidence interval describes a range of possible effects (of a treatment or intervention) that are consistent with the results of a study or group of studies. A wide confidence interval indicates a lack of certainty or precision about the true size of the clinical effect and is seen in studies with too few patients. Where confidence intervals are narrow they indicate more precise estimates of effects and a larger sample of patients studied. It is usual to interpret a ‘95%’ confidence interval as the range of effects within which we are 95% confident that the true effect lies.

Confounder or confounding factor

Something that influences a study and can contribute to misleading findings if it is not understood or appropriately dealt with. For example, if a group of people exercising regularly and a group of people who do not exercise have an important age difference then any difference found in outcomes about heart disease could well be due to one group being older than the other rather than due to the exercising. Age is the confounding factor here and the effect of exercising on heart disease cannot be assessed without adjusting for age differences in some way.

Consensus methods

A variety of techniques that aim to reach an agreement on a particular issue. In the development of clinical guidelines, consensus methods may be used where there is a lack of strong research evidence on a particular topic.

Consensus statement

A statement of the advised course of action in relation to a particular clinical topic, based on the collective views of a body of experts.


The extent to which the conclusions of a collection of studies used to support a guideline recommendation are in agreement with each other.

Control group

A group of patients recruited into a study that receives no treatment, a treatment of known effect, or a placebo (dummy treatment) – in order to provide a comparison for a group receiving an experimental treatment, such as a new drug.

Controlled clinical trial (CCT)

A study testing a specific drug or other treatment involving two (or more) groups of patients with the same disease. One (the experimental group) receives the treatment that is being tested, and the other (the comparison or control group) receives an alternative treatment, a placebo (dummy treatment) or no treatment. The two groups are followed up to compare differences in outcomes to see how effective the experimental treatment was. A CCT where patients are randomly allocated to treatment and comparison groups is called a randomised controlled trial.


A group of chemical substances produced in the body by the adrenal glands. They have many actions, including regulation of carbohydrate, fat and protein metabolism, water and electrolyte balance, and the development and maintenance of sex characteristics. They can be made artificially and have many clinical uses – when given to pregnant women (antenatal corticosteroids), they can enhance fetal lung maturation, thus helping to reduce the incidence of respiratory distress in babies born preterm.


Value for money. A specific healthcare treatment is said to be ‘cost-effective’ if it gives a greater health gain than could be achieved by using the resources in other ways.

Cost-effectiveness analysis

A type of economic evaluation comparing the costs and the effects on health of different treatments. Health effects are measured in ‘health-related units’, for example the cost of preventing one additional heart attack.


The inner layer of the wall of the uterus.

Decision analysis

The study of how people make decisions or how they should make decisions. There are several methods that decision analysts use to help people to make better decisions, including decision trees.

Decision tree

A method for helping people to make better decisions in situations of uncertainty. It illustrates the decision as a succession of possible actions and outcomes. It consists of the probabilities, costs and health consequences associated with each option. The overall effectiveness or overall cost-effectiveness of different actions can then be compared.

Declaration of interest

A process by which members of a working group or committee ‘declare’ any personal or professional involvement with a company (or related to a technology) that might affect their objectivity, for example if their position or department is funded by a pharmaceutical company.

Dehiscence of uterine scar

Splitting open during labour of the site of a previous incision in the uterus. There may be catastrophic bleeding with potential death of the woman and/or baby.


A term used in health economics describing when an option for treatment is both less clinically effective and more costly than an alternative option. The less effective and more costly option is said to be ‘dominated’.

Doppler ultrasound

A widely used clinical investigation where ultrasound, utilising the Doppler effect, is used to measure blood flow velocity in fetal blood vessels. A probe is placed on the woman’s abdomen and the area in question, such as the umbilical arteries, is identified with the ultrasound beam. The Doppler effect is employed to determine the speed and direction of blood flow in the vessel. Absent or reversed flow in the umbilical artery may indicate potential fetal compromise.

Economic evaluation

A comparison of alternative courses of action in terms of both their costs and consequences. In health economic evaluations the consequences should include health outcomes.


Softening and shortening of the cervix.


See clinical effectiveness.


The extent to which a specific treatment or intervention, under ideally controlled conditions (e.g. in a laboratory), has a beneficial effect on the course or outcome of disease compared with no treatment or other routine care.


A term for clinical procedures that are planned rather than becoming necessary as emergencies.

Electronic fetal monitoring (EFM)

See cardiotocography.


Inflammation of the inner layer of the uterus (endometrium) caused by infection. It is characterised by maternal fever, tender uterus and drainage of foul-smelling liquor.


The study of diseases within a population, covering the causes and means of prevention.


Epidural analgesia is a clinical intervention made to relieve the pain of labour. A thin catheter is inserted by an anaesthetist through the lower back into a space around the outer covering of the spinal cord (the epidural space). Analgesic drugs are injected via the catheter and repeated at intervals as necessary during labour.

Evidence based

The process of systematically finding, appraising and using research findings as the basis for clinical decisions.

Evidence-based clinical practice

Evidence-based clinical practice involves making decisions about the care of individual patients based on the best research evidence available rather than basing decisions on personal opinions or common practice (which may not always be evidence based). Evidence-based clinical practice therefore involves integrating individual clinical expertise and patient preferences with the best available evidence from research.

Evidence table

A table summarising the results of a collection of studies which, taken together, represent the evidence supporting a particular recommendation or series of recommendations in a guideline.

Expectant management

Allowing labour to develop and progress under supervision without intervention, unless clinically indicated.

Extra-amniotic infusion

Introduction of fluids or drugs between the uterus and the fetal membranes, but not in contact with the amniotic fluid or fetus.


The application of research evidence based on studies of a specific population to another population with similar characteristics.

Failed induction

Failure to establish labour after one cycle of treatment, consisting of the insertion of two vaginal PGE2 tablets (3 mg) or gel (1–2 mg) at 6-hourly intervals, or one PGE2 pessary (10 mg) within 24 hours.

Favourable cervix

The cervix is said to be favourable when its characteristics suggest there is a high chance of spontaneous onset of labour, or of responding to interventions made to induce labour.

Fetal growth restriction

Failure of adequate growth of the fetus in the womb. Ultrasound is used to estimate fetal weight and other measures of somatic growth. These measurements are compared with those expected for the gestational age of the fetus. A fetus can be smaller than expected but entirely normal. Poor growth of the fetus on repeated measurement usually indicates inadequate delivery of nutrition from the placenta, but can also be due to other processes such as intrauterine infection or chromosomal disorders. A fetus with growth restriction may be at a greater risk of stillbirth, birth asphyxia, neonatal complications and abnormal neurodevelopment. Previously known as intrauterine growth restriction (IUGR).

Fetal monitoring

The wellbeing of the fetus may be monitored during labour, by intermittent auscultation with a Pinard stethoscope, continuous cardiotocography or as required by ultrasound. Disturbances of heart rate pattern may indicate a need for intervention.

Focused question

A study question that clearly identifies all aspects of the topic that are to be considered while seeking an answer. Questions are normally expected to identify the patients or population involved, the treatment or intervention to be investigated, what outcomes are to be considered, and any comparisons that are to be made. For example, do nitric oxide donors (intervention) improve cervical scores (outcome) in women undergoing induction of labour (population) when compared with vaginal prostaglandins (comparison)? See also clinical question.

Gestational age

The age of the fetus or newborn calculated from the number of completed weeks since the first day of the woman’s last menstrual period.

Glyceryl trinitrate

A liquid chemical that is used therapeutically to relax smooth muscle, particularly as a treatment for angina pectoris (cardiac pain).

Grand multipara

A woman who has given birth to six or more babies.

Group B streptococcus (GBS)

GBS is a bacterium that is found normally in the vagina or rectum of 25% of women. Untreated, it can cause serious illness or death in the baby.


A systematically developed tool that describes aspects of a patient’s condition and the care to be given. A good guideline makes recommendations about treatment and care, based on the best research available, rather than opinion. It is used to assist clinician and patient decision making about appropriate health care for specific clinical conditions.

Guideline recommendation

Course of action advised by the Guideline Development Group on the basis of their assessment of the supporting evidence.

Health economics

A branch of economics that studies decisions about the use and distribution of healthcare resources.

Hierarchy of evidence

An established hierarchy of study types, based on the degree of certainty that can be attributed to the conclusions that can be drawn from a well-conducted study. Well-conducted randomised controlled trials (RCTs) are at the top of this hierarchy. (Several large statistically significant RCTs which are in agreement represent stronger evidence than, say, one small RCT.) Well-conducted studies of patients’ views and experiences would appear at a lower level in the hierarchy of evidence.

Incremental cost-effectiveness ratio (ICER)

A ratio of the extra (incremental) cost incurred for an additional unit of benefit gained (e.g. cost per life year gained or cost per QALY) of an intervention relative to an appropriate comparator.

Induction agent

A substance used to initiate labour.

Induction of labour

The artificial initiation of labour.

Intention-to-treat analysis

An analysis of a clinical trial where patients are analysed according to the group to which they were initially randomly allocated, regardless of whether or not they had dropped out, fully complied with the treatment or crossed over and received the alternative treatment. Intention-to-treat analyses are favoured in assessments of clinical effectiveness because they maintain the balance in basic characteristics between groups achieved by random allocation. Moreover, they mirror the non-compliance and treatment changes that are likely to occur when the treatment is used in practice.


Healthcare action intended to benefit the patient, for example drug treatment, surgical procedure, psychological therapy, etc.

Intracervical catheter

A flexible tube that is passed through the cervix to allow introduction of drugs or fluids into the uterus.


During labour.

Intrauterine death

Death of the fetus inside the uterus before birth.

Intrauterine infection

An infection of the fetus acquired while it is in the womb. The infection may cross the placenta from the mother’s circulation (e.g. many viral infections) or enter via the birth canal particularly when the membranes have ruptured prematurely (e.g. some bacterial infections).


Placed into the vagina

Isosorbide mononitrate

A nitric oxide donor, which acts to dilate smooth muscle.

Laminaria tent

A stick-shaped preparation made from dried stems of Laminaria seaweeds. They absorb fluid and swell to 3–5 times their original diameter, and thus when placed through the cervix they can produce cervical dilation as they expand. Their use has been associated with maternal or neonatal infection.

Last menstrual period

Pregnancies are dated in weeks starting from the first day of a woman’s last menstrual period. If her menstrual periods are regular and ovulation occurs on day 14 of her cycle, conception takes place about 2 weeks after her last menstrual period. The calculation of dates may be less accurate if the woman has irregular periods or has conceived after discontinuing the oral contraceptive pill.

Level of evidence

A code (e.g. 1++, 1+) linked to an individual study, indicating where it fits into the hierarchy of evidence and how well it has adhered to recognised research principles.

Literature review

A process of collecting, reading and assessing the quality of published (and unpublished) articles on a given topic.


This describes a large fetus or baby whose weight is greater than the 90th percentile for the gestational age.

Mechanical methods

Non-pharmacological means of inducing labour.

Meconium staining

Meconium is the greenish-black sticky material passed from the baby’s bowels after birth. In some instances, the fetus will pass meconium into the amniotic fluid while still in the womb, indicated by the presence of meconium staining of the liquor after the membranes have ruptured. Meconium staining is more common approaching and after term. It may indicate the presence of fetal distress in labour, but not universally so. During fetal distress, fetal acidosis may stimulate the fetus to gasp and inhale meconium into the airways and lungs, a condition known as neonatal meconium aspiration syndrome.

Membrane sweeping

A procedure where a midwife or doctor will ‘sweep’ a finger around the cervix during an internal examination. The aim is to separate the fetal membranes from the cervix, leading to a release of prostaglandins and subsequent onset of labour.


The results from a collection of independent studies (investigating the same treatment) are pooled, using statistical techniques to synthesise their findings into a single estimate of a treatment effect. Where studies are not compatible, for example because of differences in the study populations or in the outcomes measured, it may be inappropriate or even misleading to statistically pool results in this way. See also systematic review.

Methodological quality

The extent to which a study has conformed to recognised good practice in the design and execution of its research methods.


The overall approach of a research project, for example the study will be a randomised controlled trial, of 200 people, over 1 year.

Multicentre study

A study where subjects were selected from different locations or populations, for example a cooperative study between different hospitals; an international collaboration involving patients from more than one country.


A woman who has given birth to more than one baby.


A newborn baby aged 0–28 days.


A woman who has never given birth to a live infant.

Number needed to treat

This measures the impact of a treatment or intervention. It states how many patients need to be treated with the treatment in question in order to prevent an event which would otherwise occur. For example, if the NNT = 4, then four patients would have to be treated to prevent one bad outcome. The closer the NNT is to 1, the better the treatment is. Analogous to the NNT is the number needed to harm (NNH), which is the number of patients that would need to receive a treatment to cause one additional adverse event. For example, if the NNH = 4, then four patients would have to be treated for one bad outcome to occur.

Odds ratio

Odds are a way of representing probability, especially familiar for betting. In recent years odds ratios have become widely used in reports of clinical studies. They provide an estimate (usually with a confidence interval) for the effect of a treatment. Odds are used to convey the idea of ‘risk’ and an odds ratio of 1 between two treatment groups would imply that the risks of an adverse outcome were the same in each group. For rare events the odds ratio and the relative risk (which uses actual risks and not odds) will be very similar. See also relative risk, risk ratio.


Female sex hormones produced by the ovary and placenta. They are involved in making the uterus ready for the implantation and support of the early embryo. They can be produced artificially and have a number of clinical uses, such as oral contraceptives and hormone replacement therapy.


The end result of care and treatment and/or rehabilitation. In other words, the change in health, functional ability, symptoms or situation of a person, which can be used to measure the effectiveness of care/treatment/rehabilitation. Researchers should decide what outcomes to measure before a study begins; outcomes are then assessed at the end of the study.


A hormone released naturally from the pituitary gland that stimulates the contraction of the uterus during labour and facilitates ejection of milk from the breast during nursing. It can be made artificially and is used therapeutically to induce or augment labour.

P value

If a study is done to compare two treatments then the P value is the probability of obtaining the results of that study, or something more extreme, if there really was no difference between treatments. (The assumption that there really is no difference between treatments is called the ‘null hypothesis’.) Suppose the P value was P = 0.03. What this means is that if there really was no difference between treatments then there would only be a 3% chance of getting the kind of results obtained. Since this chance seems quite low we should question the validity of the assumption that there really is no difference between treatments. We would conclude that there probably is a difference between treatments. By convention, where the value of P is below 0.05 (i.e. less than 5%) the result is seen as statistically significant. Where the value of P is 0.001 or less, the result is seen as highly significant. P values just tell us whether an effect can be regarded as statistically significant or not. In no way do they relate to how big the effect might be, for which we need the confidence interval.


The number of times a woman has given birth. A woman who has given birth a particular number of times is referred to as para 1, para 2, etc.


Pertaining to parity.


The perinatal period is the time between 28 weeks of gestation and 7 completed days after birth.


A drug-containing suppository that is placed in the vagina.

Pinard stethoscope

A trumpet-shaped device used to listen to the fetal heart. The bell-shaped end is placed on the woman’s abdomen and the user’s ear placed to the other. It is named after Adolphe Pinard (1844–1934), a French obstetrician.


Placebos are fake or inactive treatments received by participants allocated to the control group in a clinical trial that are indistinguishable from the active treatments being given in the experimental group. They are used so that participants are ignorant of their treatment allocation in order to be able to quantify the effect of the experimental treatment over and above any placebo effect due to receiving care or attention.


The afterbirth. This is a complex vascular structure that allows passage of nutrients and oxygen from the woman’s circulation to the fetus, and waste substances from the fetus to the woman, without direct contact between their two circulations. In addition, the placenta is metabolically active, producing hormones and other substances essential to the maintenance of the pregnancy.


After birth.


See statistical power.

Precipitate labour

Rapid progression of labour leading to birth of the baby.


A disorder specific to pregnancy. It is usually of rapid onset and characterised by raised blood pressure, excess protein in the urine, headache, puffiness of the tissues and visual disturbance. It may lead to convulsions. The cause is still not completely understood.

Prelabour rupture of membranes

Rupture of the membranes before the onset of labour. This might be caused by infection, or predispose the fetus to infection entering the womb. The membranes may rupture close to term or prematurely (before 37 weeks). The latter may be associated with preterm birth and with serious neonatal respiratory morbidity.

Primary care

Healthcare delivered to patients outside hospitals. Primary care covers a range of services provided by GPs, nurses and other healthcare professionals, dentists, pharmacists and opticians.

Primary care trust

A primary care trust is an NHS organisation responsible for improving the health of local people, developing services provided by local GPs and their teams (called primary care) and making sure that other appropriate health services are in place to meet local people’s needs.


Cervical priming is a process where the cervix is made softer and shorter, leading to onset of labour.


A woman who is giving birth for the first time.


How likely an event is to occur, for example how likely a treatment or intervention will alleviate a symptom.

Prolapsed cord

When the umbilical cord passes through the cervix before the presenting part of the fetus (usually the head). As there is a risk of cord obstruction and fetal death or disability, an emergency caesarean section is indicated.

Prolonged pregnancy

A pregnancy that has progressed beyond 42+0 weeks of gestation.

Prospective study

A study in which people are entered into the research and then followed up over a period of time with future events recorded as they happen. This contrasts with studies that are retrospective.


Any member of a group of hormone-like substances that mediate a wide range of physiological functions, such as contraction of smooth muscle. Prostaglandin E2 (PGE2; dinoprostone) ripens the cervix and stimulates uterine muscle, and is a pharmaceutical preparation used to induce labour.


A plan or set of steps that defines appropriate action. A research protocol sets out, in advance of carrying out the study, what question is to be answered and how information will be collected and analysed. Guideline implementation protocols set out how guideline recommendations will be used in practice by the NHS, both at national and local levels.

Quality-adjusted life years

A measure of health outcome that looks at both length of life and quality of life. QALYs are calculated by estimating the years of life remaining for a patient following a particular care pathway and weighting each year with a quality of life score (on a zero to one scale). One QALY is equal to one year of life in perfect health, or two years at 50% health, and so on.

Random allocation or randomisation

A method that uses the play of chance to assign participants to comparison groups in a research study, for example by using a random numbers table or a computer-generated random sequence. The aim of random allocation is to ensure that the intervention and control groups are similar with respect to all potential confounding variables.

Randomised controlled trial

A study to test a specific drug or other treatment in which people are randomly assigned to two (or more) groups: one (the experimental group) receiving the treatment that is being tested, and the other (the comparison or control group) receiving an alternative treatment, a placebo (dummy treatment) or no treatment. The two groups are followed up to compare differences in outcomes to see how effective the experimental treatment was. (Through randomisation, the groups should be similar in all aspects apart from the treatment they receive during the study.)

Relative risk

A summary measure that represents the ratio of the risk of a given event or outcome (e.g. an adverse reaction to the drug being tested) in one group of subjects compared with another group. When the ‘risk’ of the event is the same in the two groups the relative risk is 1. In a study comparing two treatments, a relative risk of 2 would indicate that patients receiving one of the treatments had twice the risk of an undesirable outcome than those receiving the other treatment. Relative risk is sometimes used as a synonym for risk ratio.

Retrospective study

A retrospective study deals with the present/past and does not involve studying future events. This contrasts with studies that are prospective.


Summary of the main points and trends in the research literature on a specified topic. A review is considered non-systematic unless an extensive literature search has been carried out to ensure that all aspects of the topic are covered and an objective appraisal made of the quality of the studies.

Risk ratio

Ratio of the risk of an undesirable event or outcome occurring in a group of patients receiving experimental treatment compared with a comparison (control) group. The term relative risk is sometimes used as a synonym for risk ratio.

Royal Colleges

In the UK medical/nursing world the term Royal Colleges, as for example in ‘The Royal College of . . .’, refers to organisations that usually combine an educational standards and examination role with the promotion of professional standards.

Rupture of membranes

When the membranes around the baby break, either spontaneously in labour (SROM) or artificially to start labour (ARM). See also prelabour rupture of membranes.


A part of the study’s target population from which the subjects of the study will be recruited. If subjects are drawn in an unbiased way from a particular population, the results can be generalised from the sample to the population as a whole.

Scottish Intercollegiate Guidelines Network

SIGN was established in 1993 to sponsor and support the development of evidence- based clinical guidelines for the NHS in Scotland.

Selection criteria

Explicit standards used by guideline development groups to decide which studies should be included and excluded from consideration as potential sources of evidence.

Small for gestational age (SGA)

When the weight of the fetus or baby is lower than expected for gestation, below the 10th or 3rd percentile for gestational age (see fetal growth restriction).

Standard deviation

A measure of the spread, scatter or variability of a set of measurements. Usually used with the mean (average) to describe numerical data.

Statistical power

The ability of a study to demonstrate an association or causal relationship between two variables, given that an association exists. For example, 80% power in a clinical trial means that the study has an 80% chance of ending up with a P value of less than 5% in a statistical test (i.e. a statistically significant treatment effect) if there really was an important difference (e.g. 10% versus 5% mortality) between treatments. If the statistical power of a study is low, the study results will be questionable (the study might have been too small to detect any differences). By convention, 80% is an acceptable level of power. See also P value.


A medicated substance usually in a tapered shape that can be introduced into the rectum or vagina. It is solid at room temperature but melts at body temperature, releasing the medication.


A study in which information is systematically collected from people (usually from a sample within a defined population).


Methodical, according to plan; not random.

Systematic review

A review in which evidence from scientific studies has been identified, appraised and synthesised in a methodical way according to predetermined criteria. May or may not include a meta-analysis.


Gestational age when a baby is normally due. Defined as being between 37 and 42 weeks of gestation.


The use of short-acting uterine relaxants such as terbutaline, in the management of uterine hyperstimulation.


The use of ultrasonic waves to image the fetus in the womb.

Unfavourable cervix

An unfavourable (unripe) cervix is suggestive that spontaneous onset of labour is unlikely. The cervix is long and firm in consistency. It must be made softer and shorter (priming) to allow labour to begin. The degree of cervical ripeness is assessed using the Bishop score.

Uterine hyperstimulation

Overactivity of the uterus as a result of induction of labour. It is variously defined as uterine tachysystole (more than five contractions per 10 minutes for at least 20 minutes) and uterine hypersystole/hypertonicity (a contraction lasting at least 2 minutes). These may or not be associated with changes in the fetal heart rate pattern (persistent decelerations, tachycardia or decreased short term variability).

Uterine hypertonicity

See uterine hyperstimulation.


Assessment of how well a tool or instrument measures what it is intended to measure.


A measurement that can vary within a study, for example the age of participants. Variability is present when differences can be seen between different people or within the same person over time, with respect to any characteristic or feature which can be assessed or measured.

Copyright © 2008, National Collaborating Centre for Women's and Children's Health.

No part of this publication may be reproduced, stored or transmitted in any form or by any means, without the prior written permission of the publisher or, in the case of reprographic reproduction, in accordance with the terms of licences issued by the Copyright Licensing Agency in the UK []. Enquiries concerning reproduction outside the terms stated here should be sent to the publisher at the UK address printed on this page.

The use of registered names, trademarks, etc. in this publication does not imply, even in the absence of a specific statement, that such names are exempt from the relevant laws and regulations and therefore for general use.

Bookshelf ID: NBK53622


Recent Activity

Your browsing activity is empty.

Activity recording is turned off.

Turn recording back on

See more...