Abstract
Background
Monoamniotic twin pregnancies are formed when a single egg is fertilised and the resulting inner cell mass splits to form twins sharing the same amniotic sac. This condition is rare and affects about one in 10,000 pregnancies overall. Monoamniotic twin pregnancies are susceptible to complications including cord entanglement, increased congenital anomalies, intrauterine growth restriction, twin‐to‐twin transfusion syndrome and increased perinatal mortality. All twin pregnancies also carry additional maternal risks including pre‐eclampsia, anaemia, antepartum haemorrhage, postpartum haemorrhage and operative delivery.
The optimal timing for the delivery of monoamniotic twins is not known. The options include 'planned early delivery' between 32 and 34 weeks, or alternatively awaiting spontaneous labour at least up until the usual time of planned delivery for other monochorionic twins (approximately 36 to 38 weeks' gestation), unless there is a specific indication for earlier delivery.
Objectives
To assess whether routine early delivery in monoamniotic twin pregnancies improves fetal, neonatal or maternal outcomes compared with 'expectant management'. Expectant management means awaiting spontaneous labour at least up until the usual time of planned delivery for other monochorionic twins (approximately 36 to 38 weeks' gestation in many centres), unless a specific indication for delivery occurs in the meantime, e.g. for non‐reassuring antenatal testing.
Search methods
We searched the Cochrane Pregnancy and Childbirth Group's Trials Register (31 March 2015).
Selection criteria
Published and unpublished randomised controlled trials (including cluster‐randomised trials) comparing outcomes for women and infants who were randomised to planned early delivery of a monoamniotic twin pregnancy with outcomes for women and infants who were randomised to either planned term delivery or expectant management. However, we did not identify any trials for inclusion in this review.
Quasi‐randomised controlled trials, trials published in abstract form only, and trials using a cross‐over design are not eligible for inclusion in this review.
Data collection and analysis
No trials were identified by the search strategy.
Main results
No trials were identified by the search strategy.
Authors' conclusions
Monoamniotic twins are rare, and there is insufficient randomised controlled evidence on which to draw strong conclusions about the best management. In their absence, we can refer to historical case series and expert consensus. Management plans should take into consideration the availability of high‐quality neonatal care if early delivery is chosen. Women and their families should be involved in the decision making about these high‐risk pregnancies.
Ongoing, multicentre audits of maternal and perinatal outcomes for monoamniotic twins are needed in order to inform families and clinicians about up‐to‐date perinatal outcomes with contemporary obstetric practice. Research should consider the social and economic implications of planned interventions, as well as the perinatal outcomes.
Plain language summary
Monoamniotic twins (sharing the same amniotic sac): do they do better if born early?
What is the issue?
Identical twins who share the same amniotic sac in the uterus are called monoamniotic twins. The amniotic sac is the bag of waters (amniotic fluid) surrounding the baby. Monoamniotic twins are different from the majority of identical twins, who are separated from each other in their own amniotic sac, with their own amniotic fluid.
Pregnancies with monoamniotic twins are rare – about one in every 10,000 pregnancies is affected, or about 1 per cent of all incidences of identical twins. Monoamniotic twin pregnancies have risks – beyond the risks which apply to all types of twin pregnancy – and these increased risks include the death of both or one of the twins. The higher risks are mostly because the umbilical cords may become compressed, which can be dangerous because these stop the cord from getting oxygen to the baby.
We wanted to find out if it is better to ensure an earlier birth for monoamniotic twins through induction or caesarean section (‘planned early birth’) before 34 weeks pregnancy, or to wait until later, about 36‐38 weeks (or until labour starts by itself), keeping a close check on the pregnancy and the twins throughout the pregnancy (‘expectant management’).
Why is this important?
Monoamniotic twin pregnancies have higher risks than other types of twin pregnancy and these increased risks include the death of both or one of the twins. It could be that making sure the twins are born early – before 34 weeks – reduces the risk of cord compression. However, the effects of preterm birth can be serious, too, and the need for hospital care for some time is almost certain.
What evidence did we find?
We looked for randomised controlled trials comparing the outcomes of planned early birth versus expectant management (search date 31 March 2015). We looked for trials in all languages, and with no date restrictions. We did not find any.
There are case series studies and expert clinical opinions, but these types of studies cannot be relied upon to provide a clear answer unless they include very large numbers and are properly assessed for quality.
What does this mean?
Women and their families should discuss with their healthcare providers what the best option is for them. Part of that discussion will include whether high quality neonatal care is available, if early birth is chosen.
Because a randomised controlled trial would be difficult with such a rare problem, we think further research will come from bringing together the results from many different hospitals, along with the social aspects involved.
Background
Description of the condition
Twin pregnancies make up about 1.4% of pregnancies. Twenty per cent of these pregnancies consist of monochorionic twins (where the fetuses share a placenta) and 5% of monochorionic twins are monoamniotic (where the fetuses are in the same amniotic sac). Monoamniotic pregnancies are formed when a single egg is fertilised and the resulting inner cell mass splits after day nine.Monoamniocity is a rare condition affecting about one in 10,000 pregnancies.
The presence of both fetuses in the same amniotic sac commonly leads to cord entanglement and this may result in cord accidents and fetal death. In addition, monoamniotic twins are susceptible to the complications faced by all monochorionic twins including preterm birth, increased congenital anomalies, intrauterine growth restriction, twin‐to‐twin transfusion syndrome and increased perinatal mortality. All twin pregnancies also carry additional maternal risks including pre‐eclampsia, anaemia, antepartum haemorrhage, postpartum haemorrhage and operative delivery.
Monoamniotic twin pregnancies in the current era are associated with a perinatal mortality of approximately 15% in pregnancies after 20 weeks' gestation (Allen 2001; Hack 2009; Morikawa 2012), although previously this has been reported to be as high as 70% (Beasley 1999). Overall perinatal mortality for all monochorionic twins is approximately 8% (Ortibus 2009) and much of the excess perinatal mortality for monoamniotic twins is thought to be due to cord entanglement (Su 2002). All twin pregnancies are associated with a higher maternal and fetal complication rate than singleton pregnancies, but none more so than monoamniotic twins.
Description of the intervention
This review attempts to answer the question regarding the optimal timing of delivery of monoamniotic twins.
The options for management include delivering all monoamniotic twins at a predetermined gestation, such as 32 or 34 weeks, 'planned early delivery' or alternatively 'expectant management'. Expectant management means waiting for spontaneous labour at least up until the usual time of planned delivery for other monochorionic twins (approximately 36 to 38 weeks' gestation in many centres), unless there is a specific indication for delivery in the meantime, e.g. for non‐reassuring antenatal testing.
Although the review discusses timing of delivery, it is also important to note that the standard practice for the management of monoamniotic twins is widely variable with regard to antenatal ultrasound and cardiotocography (CTG) surveillance regimens. These factors may also have an independent role to play in maternal and neonatal outcomes. Published regimens for antenatal surveillance of monoamniotic twins vary from ultrasound and CTG testing every two weeks to prolonged admission to hospital from as early as 26 weeks' gestation with CTG testing up to three times each day (Heyborne 2005; Van Mieghem 2014). Most centres plan to deliver all monoamniotic twins by caesarean section; however, this is not universal, and some centres deliver selected monoamniotic twins vaginally.
We aim to determine whether a policy of planned delivery at a predetermined, premature gestation results in improved maternal and perinatal outcomes compared to a policy of 'expectant management' as defined above.
How the intervention might work
Many authors have commented that early delivery will reduce the perinatal risks of monoamniotic twins, by delivering the babies before a catastrophic event such as cord occlusion associated with entanglement, with consequent death of one or both babies, occurs (Dickinson 2005; Pasquini 2006; Roque 2003). Others have stated that this risk is minimal after 32 weeks' gestation because less fetal movement occurs with increasing fetal size and relatively decreased amniotic fluid (Tessen 1991). It has also been stated that early detection of impending fetal death is possible by detection of cardiotocographic changes present when cord compression occurs (Rodis 1997). These potential benefits of reducing fetal death by early delivery must be balanced against the neonatal risks of prematurity; the medical, psychological, social and financial implications for the mother of intensive inpatient or outpatient surveillance regimens; and cost implications for the health service. Consideration of the neonatal risks must include not only mortality, but short‐ and long‐term morbidity. Increasing evidence suggests that even late preterm birth has important long‐term health and neurodevelopmental risks for the child (Boyle 2012; Quigley 2012).
Why it is important to do this review
Monoamniotic twin pregnancies are uncommon, and are associated with high rates of poor outcomes. Individual centres and clinicians are unlikely to care for enough women to gain experience in the best form of management of these complicated pregnancies. Much of the literature regarding monoamniotic twin pregnancy and optimal management is based on small case series, often collected over a lengthy period of time, with changing obstetric and neonatal practices, and the potential problems of both positive and negative publication bias. The interventions that are proposed to reduce perinatal mortality may carry a high rate of perinatal and maternal risks, and so it is important to base management decisions on high‐quality evidence.
Objectives
To assess whether routine early delivery in monoamniotic twin pregnancies improves fetal, neonatal or maternal outcomes compared with 'expectant management'.
Methods
Criteria for considering studies for this review
Types of studies
All published and unpublished randomised controlled trials, including cluster‐randomised trials, that compare outcomes for women and infants who were randomised to planned early delivery of a monoamniotic twin pregnancy with outcomes for women and infants who were randomised to either planned term delivery or expectant management. We did not plan to include quasi‐randomised trials, cross‐over trials or trials published only as abstracts.
Types of participants
Women with an antenatally diagnosed monoamniotic twin pregnancy, excluding women with other serious twin complications (twin‐to‐twin transfusion syndrome, twin reversed arterial perfusion, serious fetal anomaly, conjoined twins, intrauterine growth restriction) or higher order multiples.
Types of interventions
Planned early delivery before 34 completed weeks' gestation compared with other types of care.
Types of outcome measures
Primary outcomes
Perinatal death or serious neonatal morbidity (e.g. severe birth asphyxia, seizures, neonatal encephalopathy, serious birth trauma, severe respiratory distress syndrome, prolonged neonatal intensive care unit admission; or as defined by trial authors).
Secondary outcomes
Short‐term perinatal/neonatal morbidity
Fetal death.
Neonatal death.
Arterial cord blood pH less than 7.0.
Neonatal intensive care unit admission.
Prolonged hospital admission, as defined by trial authors.
Neonatal encephalopathy, as defined by trial authors.
Intraventricular haemorrhage: grade III or IV.
Cystic periventricular leukomalacia.
Septicaemia.
Necrotising enterocolitis.
Assisted ventilation 24 hours or more.
Breast fed at hospital discharge.
Long‐term infant outcomes
Cerebral palsy.
Intellectual disability.
Short‐term maternal outcomes
Postpartum haemorrhage, as defined by the trial authors.
Blood transfusion.
Prolonged hospital stay.
Venous thromboembolus.
Woman not satisfied with care.
Longer‐term maternal outcomes (at one to six months)
Postnatal depression, as defined by trial authors.
Health services
Cost.
Search methods for identification of studies
The following methods section of this review is based on a standard template used by the Cochrane Pregnancy and Childbirth Group.
Electronic searches
We searched the Cochrane Pregnancy and Childbirth Group’s Trials Register by contacting the Trials Search Co‐ordinator (31 March 2015).
The Cochrane Pregnancy and Childbirth Group’s Trials Register is maintained by the Trials Search Co‐ordinator and contains trials identified from:
monthly searches of the Cochrane Central Register of Controlled Trials (CENTRAL);
weekly searches of MEDLINE (Ovid);
weekly searches of Embase (Ovid);
monthly searches of CINAHL (EBSCO);
handsearches of 30 journals and the proceedings of major conferences;
weekly current awareness alerts for a further 44 journals plus monthly BioMed Central email alerts.
Details of the search strategies for CENTRAL, MEDLINE, Embase and CINAHL, the list of handsearched journals and conference proceedings, and the list of journals reviewed via the current awareness service can be found in the ‘Specialized Register’ section within the editorial information about the Cochrane Pregnancy and Childbirth Group.
Trials identified through the searching activities described above are each assigned to a review topic (or topics). The Trials Search Co‐ordinator searches the register for each review using the topic list rather than keywords.
Searching other resources
We planned to search reference lists of retrieved studies.
We did not apply any date or language restrictions to the search.
Data collection and analysis
In this version of the review no relevant trials were identified by the search strategy. If relevant trials are identified in the future we will use the methods set out in Appendix 1 for assessing eligibility, data extraction, assessment of risk of bias and data analysis.
Results
Description of studies
Results of the search
There were no trial reports in the Pregnancy and Childbirth Group's Trials Register.
Risk of bias in included studies
No trials were identified for inclusion in the review.
Effects of interventions
No trials were identified for inclusion in the review.
Discussion
This review did not identify any trials for inclusion.
While there is insufficient good quality randomised controlled trial evidence to guide the timing of birth for monoamniotic twins, there is a body of expert opinion to draw on. The largest published series of monoamniotic twins specifically addresses the issue of timing of delivery and significant neonatal complication, and recommends delivery at 33 weeks' gestation (Van Mieghem 2014). Other experts, based on published case series, and a survey of maternal fetal medicine specialists in the USA, suggest delivery should take place between 32 and 34 weeks' gestation (DeFalco 2006; Desai 2012; Dickinson 2005; Ezra 2005; Roque 2003).
Authors' conclusions
Implications for practice.
There are no randomised controlled trial data available to guide decision making as to whether routine early delivery in monoamniotic twin pregnancies improves fetal, neonatal or maternal outcomes compared with 'expectant management'. In their absence, we can refer to historical case series and expert consensus. Management plans should take into consideration the availability of high‐quality neonatal care if early delivery is chosen. Women and their families should be involved in the decision making about these high‐risk pregnancies
Implications for research.
Due to the difficulties of performing good quality randomised controlled trials in this group of pregnant women, further research should be by other methods. Ongoing, multicentre audit of maternal and perinatal outcomes for monoamniotic twins should be performed in order to inform families and clinicians about up‐to‐date perinatal outcomes with contemporary obstetric practice. Research should consider the social and economic implications of planned interventions, as well as the perinatal outcomes. National or international registries may be the most appropriate method to facilitate comprehensive audit.
What's new
| Date | Event | Description |
|---|---|---|
| 17 May 2016 | Amended | We have added a revised plain language summary. |
History
Protocol first published: Issue 11, 2010 Review first published: Issue 4, 2015
| Date | Event | Description |
|---|---|---|
| 11 June 2015 | Amended | Added Acknowledgements statement. |
Acknowledgements
Therese Dowswell (Cochrane Pregnancy and Childbirth Group) assisted with the review, she is supported by a grant from the National Institute for Health Research (NIHR), UK (NIHR Cochrane Programme Grant Project: 13/89/05 – Pregnancy and childbirth systematic reviews to support clinical guidelines).
This project was supported by the National Institute for Health Research, via Cochrane Infrastructure and Cochrane Cochrane Programme Grant funding to Cochrane Pregnancy and Childbirth. The views and opinions expressed therein are those of the authors and do not necessarily reflect those of the Systematic Reviews Programme, NIHR, NHS or the Department of Health.
Appendices
Appendix 1. Methods to be used in updates if relevant trials are identified
In future updates we will use the following methods based on a standard template used by the Cochrane Pregnancy and Childbirth Group.
Searching other resources
We will look for additional studies in the reference lists of the studies identified.
We will not apply any language or date restrictions.
Data collection and analysis
Selection of studies
Two review authors will independently assess for inclusion all the potential studies identified as a result of the search strategy. We will resolve any disagreement through discussion or, if required, we will consult a third person.
Data extraction and management
We will design a form to extract data. For eligible studies, two review authors will extract the data using the agreed form. We will resolve discrepancies through discussion or, if required, we will consult a third person. Data will be entered into Review Manager software (RevMan 2014) and checked for accuracy.
When information regarding any of the above is unclear, we plan to contact the authors of the original reports to provide further details.
Assessment of risk of bias in included studies
Two review authors will independently assess risk of bias for each study using the criteria outlined in the Cochrane Handbook for Systematic Reviews of Interventions (Higgins 2011). Any disagreement will be resolved by discussion or by involving a third assessor.
(1) Random sequence generation (checking for possible selection bias)
We will describe for each included study the method used to generate the allocation sequence in sufficient detail to allow an assessment of whether it should produce comparable groups.
We will assess the method as:
low risk of bias (any truly random process, e.g. random number table; computer random number generator);
high risk of bias (any non‐random process, e.g. odd or even date of birth; hospital or clinic record number);
unclear risk of bias.
(2) Allocation concealment (checking for possible selection bias)
We will describe for each included study the method used to conceal allocation to interventions prior to assignment and will assess whether intervention allocation could have been foreseen in advance of, or during recruitment, or changed after assignment.
We will assess the methods as:
low risk of bias (e.g. telephone or central randomisation; consecutively numbered sealed opaque envelopes);
high risk of bias (open random allocation; unsealed or non‐opaque envelopes, alternation; date of birth);
unclear risk of bias.
(3.1) Blinding of participants and personnel (checking for possible performance bias)
We will describe for each included study the methods used, if any, to blind study participants and personnel from knowledge of which intervention a participant received. We will consider that studies are at low risk of bias if they were blinded, or if we judge that the lack of blinding unlikely to affect results. We will assess blinding separately for different outcomes or classes of outcomes.
We will assess the methods as:
low, high or unclear risk of bias for participants;
low, high or unclear risk of bias for personnel.
(3.2) Blinding of outcome assessment (checking for possible detection bias)
We will describe for each included study the methods used, if any, to blind outcome assessors from knowledge of which intervention a participant received. We will assess blinding separately for different outcomes or classes of outcomes.
We will assess methods used to blind outcome assessment as:
low, high or unclear risk of bias.
(4) Incomplete outcome data (checking for possible attrition bias due to the amount, nature and handling of incomplete outcome data)
We will describe for each included study, and for each outcome or class of outcomes, the completeness of data including attrition and exclusions from the analysis. We will state whether attrition and exclusions were reported and the numbers included in the analysis at each stage (compared with the total randomised participants), reasons for attrition or exclusion where reported, and whether missing data were balanced across groups or were related to outcomes. Where sufficient information is reported, or is supplied by the trial authors, we plan to re‐include missing data in the analyses which we undertake.
We will assess methods as:
low risk of bias (e.g. no missing outcome data; missing outcome data balanced across groups);
high risk of bias (e.g. numbers or reasons for missing data imbalanced across groups; ‘as treated’ analysis done with substantial departure of intervention received from that assigned at randomisation);
unclear risk of bias.
(5) Selective reporting (checking for reporting bias)
We will describe for each included study how we have investigated the possibility of selective outcome reporting bias and what we found.
We will assess the methods as:
low risk of bias (where it is clear that all of the study’s pre‐specified outcomes and all expected outcomes of interest to the review have been reported);
high risk of bias (where not all the study’s pre‐specified outcomes have been reported; one or more reported primary outcomes were not pre‐specified; outcomes of interest are reported incompletely and so cannot be used; study fails to include results of a key outcome that would have been expected to have been reported);
unclear risk of bias.
(6) Other bias (checking for bias due to problems not covered by (1) to (5) above)
We will describe for each included study any important concerns we had about other possible sources of bias.
(7) Overall risk of bias
We will make explicit judgements about whether studies are at high risk of bias, according to the criteria given in the Handbook (Higgins 2011). With reference to (1) to (6) above, we plan to assess the likely magnitude and direction of the bias and whether we consider it is likely to impact on the findings. We will explore the impact of the level of bias through undertaking sensitivity analyses ‐ see Sensitivity analysis.
Measures of treatment effect
Dichotomous data
For dichotomous data, we will present results as summary risk ratio with 95% confidence intervals.
Continuous data
We will use the mean difference if outcomes are measured in the same way between trials. We will use the standardised mean difference to combine trials that measure the same outcome, but use different methods.
Unit of analysis issues
Cluster‐randomised trials
We will include cluster‐randomised trials in the analyses along with individually‐randomised trials. We will adjust their sample sizes using the methods described in the Handbook using an estimate of the intracluster correlation co‐efficient (ICC) derived from the trial (if possible), from a similar trial or from a study of a similar population. If we use ICCs from other sources, we will report this and conduct sensitivity analyses to investigate the effect of variation in the ICC. If we identify both cluster‐randomised trials and individually‐randomised trials, we plan to synthesise the relevant information. We will consider it reasonable to combine the results from both if there is little heterogeneity between the study designs and the interaction between the effect of intervention and the choice of randomisation unit is considered to be unlikely.
We will also acknowledge heterogeneity in the randomisation unit and perform a subgroup analysis to investigate the effects of the randomisation unit.
Cross‐over trials
Cros‐over trials are not a relevant design for this type of intervention.
Other unit of analysis issues
For the neonatal data, we will seek statistical advice to correct the confidence intervals to allow for the cluster effect of randomisation of the babies in pairs.
Dealing with missing data
For included studies we will note levels of attrition and if there are several studies included, the impact of including studies with high levels of missing data in the overall assessment of treatment effect will be explored by using sensitivity analysis.
For all outcomes, analyses will be carried out, as far as possible, on an intention‐to‐treat basis, i.e. we will attempt to include all participants randomised to each group in the analyses. The denominator for each outcome in each trial being the number randomised minus any participants whose outcomes are known to be missing.
Assessment of heterogeneity
We will assess statistical heterogeneity in each meta‐analysis using the Tau², I² and Chi² statistics. We will regard heterogeneity as substantial if an I² is greater than 30% and either a Tau² is greater than zero, or there is a low P value (less than 0.10) in the Chi² test for heterogeneity. If we identify substantial heterogeneity (above 30%), we plan to explore it by pre‐specified subgroup analysis.
Assessment of reporting biases
If there are 10 or more studies in the meta‐analysis, we will investigate reporting biases (such as publication bias) using funnel plots. We will assess funnel plot asymmetry visually. If asymmetry is suggested by a visual assessment, we will perform exploratory analyses to investigate it.
Data synthesis
We will carry out statistical analysis using the Review Manager software (RevMan 2014). We will use fixed‐effect meta‐analysis for combining data where it is reasonable to assume that studies are estimating the same underlying treatment effect: i.e. where trials examine the same intervention, and the trials’ populations and methods are judged sufficiently similar.
If there is clinical heterogeneity sufficient to expect that the underlying treatment effects differ between trials, or if substantial statistical heterogeneity is detected, we will use random‐effects meta‐analysis to produce an overall summary, if an average treatment effect across trials is considered clinically meaningful. The random‐effects summary will be treated as the average range of possible treatment effects and we will discuss the clinical implications of treatment effects differing between trials. If the average treatment effect is not clinically meaningful, we will not combine trials. If we use random‐effects analyses, the results will be presented as the average treatment effect with 95% confidence intervals, and estimates of Tau² and I².
Subgroup analysis and investigation of heterogeneity
If we identify substantial heterogeneity, we will investigated it using subgroup analyses.
We plan to carry out the following subgroup analyses:
planned delivery before 32 completed weeks' gestation versus other form of care;
intensive surveillance versus routine surveillance.
We will use the following outcome in subgroup analysis:
perinatal death (excluding fatal anomalies) or serious neonatal morbidity (e.g. severe birth asphyxia, seizures, neonatal encephalopathy, serious birth trauma, severe respiratory distress syndrome, prolonged neonatal intensive care unit admission; or as defined by trial authors).
We will assess differences between subgroups by interaction tests available within RevMan (RevMan 2014). We will report the results of subgroup analyses quoting the Chi² statistic and P value, and the interaction test I² value.
Sensitivity analysis
We plan to carry out sensitivity analyses to explore the effect of trial quality assessed by concealment of allocation, high attrition rates, or both, with poor quality studies being excluded from the analyses in order to assess whether this makes any difference to the overall result.
Differences between protocol and review
The methods text has been updated in line with the most recent standard methods text used by the Cochrane Pregnancy and Childbirth Group.
We have edited the secondary outcome 'Prolonged hospital admission' to 'Prolonged hospital admission, as defined by the trial authors'.
Contributions of authors
SP Walker reviewed the topic and contributed to the protocol and review development. A Shub prepared a first draft of the review and is the guarantor for the review.
Sources of support
Internal sources
No sources of support supplied
External sources
-
National Institute for Health Research (NIHR), UK.
NIHR Cochrane Programme Grant Project: 13/89/05 – Pregnancy and childbirth systematic reviews to support clinical guidelines
Declarations of interest
None known.
Edited (no change to conclusions)
References
Additional references
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