Artificial opening of the cervix during a planned caesarean section before the start of labour for reducing postoperative problems

What is the issue?

The cervix is the narrow neck-like passage at the lower end of the uterus that enters into the vagina. A woman's cervix is firm and undilated at the beginning of pregnancy, but progressively softens, all the way to term. The progressive opening, or dilatation, of the cervix occurs with uterine contractions during labour. Mechanical dilatation of the cervix at caesarean section, before onset of labour, is the artificial opening of the cervix. It is done by the surgeon, using a gloved finger, sponge forceps, or other surgical instruments.

Why is this important?

Some obstetricians believe that dilating the cervix helps the drainage of blood from the uterus, following birth by planned caesarean section before the onset of labour. Increased drainage may reduce the risk of intrauterine infection and postpartum haemorrhage. On the other hand, mechanically opening the cervix could result in contamination of the uterus with vaginal micro-organisms, and increase the risk of infections or cervical trauma. We set out to determine the effects of mechanical dilatation of the cervix during a planned caesarean section before the onset of labour on postoperative blood loss and uterine infection, when compared with no mechanical dilatation.

What evidence did we find?

We searched for evidence from randomised controlled trials in September 2017. We identified eight studies with a total of 2227 women undergoing elective (planned) caesarean section before the onset of labour. Of these women, 1097 underwent cervical dilatation with a double-gloved index finger, or in one study with a Hegar dilator, during surgery, while 1130 did not undergo cervical dilatation during surgery.

Low- or very low-quality evidence suggested it was unclear whether cervical dilatation had any impact on postpartum haemorrhage (estimated blood loss greater than 1000 mL), the need for blood transfusion, and other measures of blood loss, postpartum haemorrhage within six weeks, febrile morbidity (infection indicated by increased temperature over a defined time period), endometritis (infection of the lining of the womb), or uterine subinvolution (uterus not returning to its normal size after childbirth). There were no data for cervical trauma.

We found a slight improvement with mechanical dilatation for some outcomes that had not been specified in our original protocol, but the evidence for these outcomes was based on one or two studies (mean blood loss, endometrial cavity thickness, retained products of conception, distortion of uterine incision, and healing ratio). Cervical dilatation did not have a clear effect on other secondary outcomes, (again not specified in our original protocol): wound infection, urinary tract infection, operative time, infectious morbidity, and integrity of uterine scar.

What does this mean?

It is uncertain whether cervical dilatation has any impact on reducing postoperative problems after caesarean section. This means there is insufficient evidence to encourage or discourage the use of mechanical dilatation of the cervix at elective caesarean section for reducing postoperative ill-health.

Authors' conclusions: 

At this time, the evidence does not support or refute the use of mechanical dilatation of the cervix during elective caesarean section for reducing postoperative morbidity.

Further large, well-designed studies are required to compare the effect of intraoperative mechanical dilatation of the cervix with no intraoperative mechanical cervical dilatation for reducing postoperative morbidity.

Read the full abstract...
Background: 

During elective (planned) caesarean sections, some obstetricians routinely dilate the cervix intraoperatively, using sponge forceps, a finger, or other instruments, because the cervix of women not in labour may not be dilated, and this may cause obstruction of blood or lochia drainage. However, mechanical cervical dilatation during caesarean section may result in contamination by vaginal micro-organisms during dilatation, and increase the risk of infection or cervical trauma.

Objectives: 

To determine the effects of mechanical dilatation of the cervix during elective caesarean section on postoperative morbidity.

Search strategy: 

We searched the Cochrane Pregnancy and Childbirth Group's Trials Register, ClinicalTrials.gov, the WHO International Clinical Trials Registry Platform (ICTRP) and reference lists of retrieved studies on 20 September 2017.

Selection criteria: 

We included all randomised, quasi-randomised, and cluster-randomised controlled trials comparing intraoperative cervical dilatation using a finger, sponge forceps, or other instruments during elective caesarean section versus no mechanical dilatation.

Data collection and analysis: 

Two review authors independently assessed trials for inclusion and risk of bias, extracted data and checked them for accuracy. We assessed the quality of the evidence using the GRADE approach.

Main results: 

We included eight studies with a total of 2227 women undergoing elective caesarean section. Of these, 1097 underwent intraoperative cervical dilatation with a double-gloved index finger or Hegar dilator inserted into the cervical canal to dilate, and 1130 did not undergo intraoperative cervical dilatation. Six of the eight included trials had high risk of bias for some of the risk of bias domains.

Very low-quality evidence suggested it was unclear whether cervical dilatation had any impact on postpartum haemorrhage (estimated blood loss greater than 1000 mL; risk ratio (RR) 1.97, 95% confidence interval (CI) 0.48 to 8.13; 5/205 versus 3/242; one study, 447 women).

Low- or very low-quality evidence showed no clear difference for the need for blood transfusion (RR 3.54, 95% CI 0.37 to 33.79; two studies, 847 women); postoperative haemoglobin (mean difference (MD -0.05, 95% CI -0.15 to 0.06; three studies, 749 women), or haematocrit (MD 0.01%, 95% CI -0.18 to 0.20; one study, 400 women); the incidence of drop from baseline haemoglobin above 0.5 g/dL (RR 0.92, 95% CI 0.64 to 1.31; two studies, 722 women), or amount of haemoglobin drop (MD -0.01 g/dL, 95% -0.14 to 0.13; three studies, 796 women); the incidence of secondary postpartum haemorrhage within six weeks (RR 1.18, 95% CI 0.07 to 18.76; one study, 447 women); febrile morbidity (RR 1.18, 95% CI 0.76 to 1.85; seven studies, 2126 women); endometritis (RR 0.94, 95% CI 0.35 to 2.52; four studies, 1536 women); or uterine subinvolution (RR 0.34, 95% CI 0.08 to 1.36; two studies, 654 women); the results crossed the line of no effect for all of the outcomes. There were no data for cervical trauma.

We found a slight improvement with mechanical dilatation for these secondary outcomes, not prespecified in the protocol: mean blood loss, endometrial cavity thickness, retained products of conception, distortion of uterine incision, and healing ratio. The evidence for these outcomes was based on one or two studies. Cervical dilatation did not have a clear effect on these secondary outcomes, not prespecified in the protocol: wound infection, urinary tract infection, operative time, infectious morbidity, and integrity of uterine scar.

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