Tuesday April 3 2012
A silicone pessary may help delay premature labour in at-risk women
"A cheap medical device can dramatically reduce the number of premature births in some at-risk women," the BBC reported today.
This news is based on a Spanish trial that looked at a cervical pessary, a small ring-shaped device which is inserted around the cervix to prevent early births. The cervix is the lower, narrow portion of the womb which joins the top of the vagina. In this study, the pessary was used in women with a short cervix (25mm or shorter). A shorter cervix indicates that a woman is at increased risk of premature labour. The study found that these pessaries reduced the number of deliveries before 34 weeks of pregnancy (early preterm birth) from 27% in women who did not use the pessary to 6% in those who did.
Spontaneous preterm birth is a leading cause of illness and death for babies. Finding a safe and effective way of reducing the number of babies born prematurely is an important and worthwhile goal, and this study has shown that the pessary has some merit. However, the study was relatively small and the authors have called for further larger studies in different countries to determine whether this intervention is effective and acceptable in routine practice. The size of this study also meant there were very few neonatal deaths and other adverse outcomes, and larger studies should ideally address these issues, as well as looking at which women would gain most benefit from use of this device. For example, should eligibility be based on cervical length alone or other risk factors for prematurity.
Where did the story come from?
The study was carried out by researchers from research institutes and universities in Spain. It was funded by the Carlos III Institute of Health. The study was published in the peer-reviewed medical journal The Lancet.
This study was accurately covered by the BBC.
What kind of research was this?
A full-term pregnancy is when a baby is born at 37 weeks of pregnancy or later. However, many women have preterm births, when their baby is delivered before 37 weeks. Preterm birth is generally associated with health problems for the baby. These problems tend to be greater the earlier the baby is born.
In current medical practice, options to try to prevent preterm birth tend to focus on identifying women at risk for having a preterm birth and managing their risk factors. For example, this could include managing diabetes and high blood pressure in pregnancy, closely monitoring women with multiple pregnancies or with a history of preterm birth, and encouraging women to stop smoking. However, interventions to try to prevent preterm labour and birth are limited.
A treatment known as cervical cerclage (where a stitch is placed to keep the cervix closed) may be used, but this technique tends to be restricted to women who have already had several preterm births or pregnancy losses. If a woman has already gone into preterm labour, drugs may be used to try to stop her contractions (tocolytic drugs). However, these drugs often have restricted use because when a woman has gone into preterm labour, it is sometimes safer, for the mother and baby, to allow the delivery to occur than to prevent it. For example, if the membranes surrounding the baby have already ruptured, there is risk of infection.
There is a need for proven methods to help safely prevent early labour and birth in women identified to be at increased risk, and hence to reduce the risk of the neonatal health problems associated with prematurity.
This randomised controlled trial (RCT) tested the use of a pessary to prevent preterm births. A pessary is a device that is inserted into the vagina, usually to support the womb or deliver medication such as anti-thrush creams. The pessary used in this study was a non-medicated silicone ring that sits around the cervix (the opening of the womb).
Pessaries have been used over the past 50 years to prevent preterm birth, although the evidence supporting their effectiveness has reportedly come from non-randomised trials. The researchers conducting this trial say it is the first RCT of the use of cervical pessaries for the prevention of preterm birth. Randomised studies generally provide better evidence than non-randomised ones, as the participants are randomly allocated to use different treatments. This eliminates bias in the results that could arise if participants were assigned a specific treatment based on their individual medical characteristics. An RCT is the ideal study design for determining whether cervical pessaries are effective in preventing preterm births.
This trial was conducted across five hospitals in Spain. Pregnant women with a short cervical length (25mm or less) were randomly assigned to receive the cervical pessary or to join a control group. Other studies have found that women with a short cervical length are at increased risk of spontaneous early preterm delivery.
What did the research involve?
The study recruited 385 women aged 18 to 42 years old who were pregnant with a single child and had a cervical length of 25mm or less, measured on an ultrasound scan. The ultrasound measurement was done during the routine second trimester ultrasound given to assess the baby’s general development. Women were randomly assigned to receive either the pessary or to be part of an “expectant management” group. Expectant management is type of “watchful waiting” during which medical staff closely monitor the progress of pregnancy but only step in with treatment if a medical need is identified.
The researchers then monitored all the women every month, and the pessary was removed after 37 weeks of pregnancy or earlier. The researchers analysed the number of women who had a spontaneous delivery before 34 weeks of pregnancy in each group, and a number of other outcomes including side effects and outcomes immediately after birth. Although births before 37 weeks are generally considered to be preterm, those occurring between 34 and 37 weeks generally have milder complications than those occurring before 34 weeks, which is often known as early preterm.
What were the basic results?
Spontaneous early preterm delivery (before 34 weeks) was significantly less frequent in the pessary group, occurring in 6% of the group compared with 27% of the group receiving expectant management (odds ratio [OR] 0.18, 95% confidence interval 0.08 to 0.37).
If all births were considered (including non-spontaneous births, such as caesarean sections), deliveries before 34 weeks occurred in 7% of the cervical pessary group and 28% of the expectant management group. This represents a 21% absolute reduction in risk, which means that only about five women with a short cervix need to be treated with this device to prevent one baby being born before 34 weeks.
Other results included:
- The average gestational age at delivery was also significantly higher in the cervical pessary group, with babies being born at 37.7 weeks of pregnancy in the pessary group compared with 34.9 weeks in the expectant management group.
- The need to suppress labour using drugs (tocolysis) and to use corticosteroid treatment (used to try to mature the baby’s lungs before birth) was significantly higher in the expectant management group.
- The pessary group included significantly fewer babies born with birth weight less than 2,500g (5.5 lbs) or with respiratory distress syndrome. There was also a reduced need for treatment of sepsis (a potentially serious bacterial infection), and a reduced rate in a composite measure of adverse outcomes in the pessary group.
- No major side effects were associated with the pessary, and only one patient needed to have the pessary removed early (less that 1% of the group).
- However, insertion and removal of the pessary was reported as painful, with a pain rating of 4 on insertion and 7 on removal (on a scale of 0 to 10). Despite this, 95% of the pessary group would recommend the intervention to other people.
How did the researchers interpret the results?
The authors said that “the cervical pessary is an affordable, safe, and reliable alternative for prevention of preterm birth in a population of appropriately selected at-risk pregnant women who have been screened for cervical length assessment at the midtrimester scan.”
In current medical practice, options for preventing preterm labour and birth tend to focus on identifying women at risk of having a preterm birth and managing their risk factors. Medical interventions to try to prevent birth and delivery are, however, limited.
This new research has focused on treatments for women found to have a short cervix (the opening to the womb), who have an increased risk of early delivery. It tested whether a simple silicone ring (pessary) placed in the vagina and over the cervix can help prevent preterm births, and found positive results for the ring.
The researchers found that pessaries in women with a short cervix (25mm or shorter) reduced the proportion of deliveries before 34 weeks of pregnancy, from 27% in women receiving standard treatment to just 6% in women given the pessary.
Pessaries of this kind have been used in medical practice for many years, but the evidence supporting their use has come from non-randomised trials. These can be influenced by bias as participants have their treatment chosen according to their circumstances. This latest trial has the benefit that patients were randomly allocated their treatment method, providing better evidence than non-randomised trials.
However, this exciting research needs to be confirmed in further larger studies of routine care in several other countries. It should also be noted that it is difficult to predict which women are likely to have a preterm birth. Only 6% of women initially screened in this study fulfilled this criteria, so we cannot tell if most pregnant women would derive any benefit from such a pessary.
Also, although gestational age at birth was increased with the pessary, the study was not large enough to assess some other important outcomes for babies. For example, the number of participants involved and the length of follow-up meant it cannot tell us about rates of rare but serious problems such as long-term illness or death, which have been linked to spontaneous preterm birth. The researchers stated that they have “planned a long-term follow-up of the infants until the age of two years to detect and compare developmental impairments in the two groups”.