Amniotomy is the deliberate rupture of the fetal membranes. It was first described over 200 years ago by Thomas Denman of the Middlesex Hospital in the United Kingdom) (Calder 1999). This procedure involves feeling the membranes vaginally and rupturing or piercing them either by fingers or instruments (Bricker 2000; Frigoletto 1995). Amniotomy has been used alone, or in combination with other interventions, both for induction and for shortening of labour (Bricker 2000). It is thought to act by releasing prostaglandins and increasing oxytocin levels (Busowski 1995; Wolomby 2009).
Induction and augmentation of labour are common obstetric practices. Trends have shown a rise in the induction rate over the last decade with rates varying from 9.5% to 33.7% of all pregnancies annually (Mackenzie 2006; Tenore 2003). Data claim that the rate of labour inductions are rising faster than the rate of pregnancy complications (Agency for Healthcare Research and Quality 2009).
There is a myriad of methods for both labour induction and augmentation including pharmacological, mechanical, complementary and alternative medicine (Hofmeyr 2009). Even though the pharmacological methods of induction of labour have become more common in recent years, amniotomy alone or amniotomy with oxytocin still remain the most common approach to induce or augment labour, particularly in resource-constrained settings (Bricker 2000; Janes 2001; Mozurkewich 2011; Tinelli 2003).
Description of the condition
Amniotomy for induction of labour
Many studies have utilised amniotomy as a method for induction of labour. This has been studied with and without the use of oxytocin (Busowski 1995; Cooley 2010; Mozurkewich 2011; Nachum 2010). Some evidence is present that amniotomy alone may necessitate the use of oxytocin more often than pharmacological methods (Bricker 2000; Mozurkewich 2011; Tinelli 2003).
Amniotomy to shorten first stage of labour
Besides induction of labour, amniotomy is commonly used to shorten labour both singly or in combination with oxytocin (Smyth 2007) and is a part of "active management of labour". Studies and reviews looking at the safety and efficacy profiles report insufficient data for the use of amniotomy alone. When considering a combination of amniotomy with oxytocin establishment of active labour, a shorter amniotomy-delivery interval, lesser maternal fever and greater maternal satisfaction has been reported (Howarth 2001; Nachum 2010; Pisal 2009).
Risks of amniotomy (infectious morbidity associated with intra-amniotic infection)
Rupture of membranes can lead to ascending infection from the vagina to the uterine cavity and, in the majority of instances is the reason for intra-amniotic infections (Heinemann 2008; Hopkins 2002). Intra-amniotic infections in turn can lead to significant maternal and fetal morbidity (Gibbs 1982; Gilstrap 1988).
Even though the actual incidence of chorioamnionitis is not known, it would be expected to be higher in the developing countries where women may receive sub-optimal care and have poor nutrition during pregnancy (Katona 2008; Naeye 1977; Reilly 2008). It is in these resource-poor settings that amniotomy would be more commonly used, either as a method of augmentation or induction (Bricker 2000; Janes 2001). The implications for the neonate too would be graver as universal Group B Streptococcus screening would not be available in these settings.
Intra-amniotic infection can lead to early onset neonatal sepsis (EONS) (Escobar 1999). Newborns who develop EONS, defined as proven infection at less than 72 hours of life, have a higher mortality rate (Dutta 2010).
Infection would also be related to the time between amniotomy and delivery. It is likely the length of time would be quite short in most cases (especially amniotomy to shorten the first stage of labour), therefore, the potential for infection might be unlikely. On the other hand, amniotomy for induction may not follow the same pattern and may result in greater infectious morbidity (Cooley 2010; Hofmeyr 2009).
Apart from the risks of amniotomy per se, there are other associated procedures that contribute to the risks of amniotomy when used either for labour augmentation or induction. These include intravenous line, electronic fetal monitoring by scalp electrode, intrauterine pressure catheters, pain-relieving drugs, immobilisation and regional anaesthesia, each of which contribute to the risks or benefits of amniotomy for induction or augmentation (Hofmeyr 2009).
Besides infectious morbidity, early amniotomy has also been associated with fetal heart abnormalities (Goffinct 1982).
Description of the intervention
The organisms commonly isolated in intra-amniotic infections are ascending genital microbes and chorioamnionitis is often poly-microbial. Ureaplasma urealyticum and Mycoplasma hominis are the most commonly isolated organisms (Kron 1995; Romero 1989; Silver 1989; Tita 2010). Besides, Gardenella vaginalis, Bacteroides species, Escherichia coli and Group B streptococci lead to intra-amniotic infection with significant maternal and neonatal morbidity (Hopkins 2002). Additionally, methicillin-resistant Staphylococcus aureus (MRSA) has been identified as a common cause of nosocomial infection in maternity and neonatal units (Bratu 2005; Zanella 2010). Listeria monocytogenes infection of the neonate has also been reported, presumably due to hematogenous spread (originating or transported in the blood) rather than ascending vaginal infection (Hopkins 2002; Schuchat 1992).
How the intervention might work
Comparison of different antibiotic regimens for intra-amniotic infections has not given any conclusive results (Hopkins 2002; Lamont 2006; Yoon 2001). Since the optimal antibiotic regimen is not established, most of the recommendations for antibiotic usage are based on consensus. A combination regimen is mostly used which combines a penicillin and an aminoglycoside. For anaerobic coverage, either clindamycin or metronidazole is often used as a third drug. Intravenous administration of ampicillin (2 g) or aqueous penicillin G (5 million Units) intravenously every six hours and gentamicin every eight to 24 hours until delivery is the typical regimen (Edwards 2005; Hopkins 2002; Locksmith 2005). Vancomycin, extended spectrum penicillins or cephalosporins such as piperacillin-tazobactam or cefotetan have also been used (Edwards 2005). In penicillin-allergic patients, vancomycin (1 g intravenously every 12 hours) may replace ampicillin (Duff 2002). For the purpose of this review, we will consider any antibiotic or combination of antibiotics used by the trial authors.
Mode of action and side effects of the commonly used antibiotics
Ampicillin is a semisynthetic derivative of penicillin used as a broad spectrum bactericidal agent against gram-positive bacteria and acts by inhibiting cell wall synthesis. As with all of the penicillin group of drugs hypersensitivity and sometimes serious anaphylaxis is reported. Antibiotic-associated diarrhoea is a common side effect (Katzung 2007; Thomas 2003; US FDA 2009). Gentamicin is an aminoglycoside, bactericidal antibiotic, which is particularly active against infections caused by gram-negative organisms. It acts by binding to ribosomes and preventing bacterial protein synthesis. Gentamycin acts as a vestibulo toxin as well as a nephrotoxin and this action is dose-related. Therefore, dosage of gentamycin has to be titrated by body weight (Falco 1969; Katzung 2007; Merck 2005). Like gentamycin,Clindamycin inhibits bacterial protein synthesis by binding to ribosomes. It has bacteriostatic action against gram-positive aerobes and anaerobes and gram-negative anaerobes. Antibiotic-associated diarrhoea is a common side effect and hypersensitivity can also occur. In the event of long-term use, liver and renal function tests should be checked (Merck 2006; Rossi 2006; Thomas 2003; US FDA 2009).
Metronidazole acts by producing intermediates that cause DNA damage (Muller 1983). Sharp, unpleasant metallic taste, furry tongue glossitis and stomatitis, reversible neutropenia (reduction in the number of white cells (neutrophils) and rarely reversible thrombocytopenia (reduction in the numbers of platelets) are the common side effects of metronidazole.
Vancomycin acts by inhibiting cell wall synthesis in gram-positive bacteria and is reserved for infections by these bacteria that do not respond to less toxic antibiotics. A common side effect of vancomycin when given intravenously is thrombophlebitis (Katzung 2007; Levine 2006; Moellering 2006; Sundin 2001).
Why it is important to do this review
Amniotomy was, and still is, a common obstetric intervention both for induction and as a part of active management of labour. This is particularly true in settings where pharmacological agents that have become more popular in the recent years cannot be used due to cost and availability constraints.
Amniotomy is an invasive procedure and often accompanied by other invasive ones giving lower genital tract organisms access to the amniotic cavity (Hopkins 2002). This could well be the argument for use of prophylactic antibiotics. Countries where screening for Group B streptococci is available are using prophylactic antibiotics in women testing positive for this organism. But this universal screening is not available in many countries, which again speaks in favour of antibiotic use. Other predisposing factors for intra-amniotic infections are: abnormal vaginal flora, obesity, drug abuse, smoking, immunodeficiency states, any of which could be present in any setting (Newton 1993).
With the use of antibiotics come other concerns. The chief being the side effects of these antibiotics on the mother and baby and also the graver issue of emergence of antibiotic-resistant strains. Administering antibiotics prior to amniotomy would prevent or lessen maternal morbidity but could lead to delay in the diagnosis of neonatal sepsis. Besides this, there is the issue of cost, again more so in low-resource settings.
We will evaluate the use of antibiotics prior to amniotomy in terms of the beneficial and harmful effects for the mother and the neonate