Do you think your waters have broken? Though usually the ‘waters’ remain intact until labour begins, approximately eight per cent of the time this can happen before labour starts. The phenomenon is also known as ‘membranes releasing’ or ‘pre-labour rupture of membranes’ (PROM). On TV, this tends to be a dramatic gush and labour immediately starts, but in real life it can be surprisingly tricky to work out what is happening when a woman starts leaking fluid via the vagina.

I’m writing here about an otherwise normal pregnancy which has got to 37 weeks gestation or more – a term pregnancy – rather than a preterm prelabour rupture of membranes, which requires a different assessment as the fetus (baby) is more vulnerable when premature. So, why is anyone concerned about a spontaneous rupture of membranes at term? Surely it’s a good thing, as prelabour rupture of membranes (PROM) (also known as spontaneous rupture of membranes (SRM)) is known as a sign that labour will often start soon. Indeed, the majority of women who experience prelabour rupture of membranes will go into labour naturally within 96 hours.

However, one of the roles of the intact sac of fluid (a balloon-like structure filled with amniotic fluid known as the ‘waters’) is to protect the baby from bacteria (and hence infection) that may be introduced via the vagina. So it’s important to be able to correctly identify if the membranes are intact (in which case the likelihood of infection is not increased), versus a rupture of membranes where the sac of fluid surrounding the baby does have a rupture (break), (because if the sac is truly ‘broken’ there may be a raised possibility of bacteria gaining access to the fluid that surrounds the baby). There are other uncommon risks when the membranes release, such as cord prolapse or cord compression, but this article focuses on the chance of infection which is usually given as the rationale for advising women to have their labour started using artificial means within the hospital setting.

If labour doesn’t start within 24 hours it has become standard practice in the UK for a woman to be offered ‘induction’ (more properly called augmentation) of labour in order to reduce the risk of infection. This is not an uncontroversial approach, because even with a known rupture of membranes, infection rates actually rise slowly and the rates of infection increase if interventions such as vaginal examinations are carried out.

Here is an excellent article by midwife Dr Rachel Reed about the decision whether to wait for labour or to intervene https://midwifethinking.com/2017/01/11/pre-labour-rupture-of-membranes-impatience-and-risk/. However, my main focus is not induction of labour itself, but whether all apparent cases of ‘rupture of membranes’ are in fact true ruptures even where amniotic fluid is released. I know this sounds mysterious, even impossible – please bear with me while I explore three of the most common scenarios.

SCENARIO ONE: THE OBVIOUS RUPTURE OF MEMBRANES

Sometimes it’s easy to understand what is happening and it is obvious that the membranes have released or ruptured. The ‘waters’ release with a gush and sometimes women feel or even hear a ‘pop’. The waters flow out copiously, the woman feels as if she is constantly losing fluid and she’s regularly soaking through pads or even towels. The fluid may be straw coloured, light pink, or possibly stained green or brown if baby has passed meconium (the first poo). In this scenario, there is no doubt about what has happened and there has been a breach of the amniotic sac. (Please see Rachel Reed’s article for a discussion of the benefits and risks of waiting rather than having an immediate augmentation of labour.)

SCENARIO TWO: THE WEEPING CERVIX

Then we have the scenario where there is a trickle of watery secretion, which may be enough to cause a damp patch … but there isn’t a continuous flow, and any trickles are usually not sufficient to soak a pad. I first heard this phenomenon described by independent midwife Jane Evans who described it as ‘cervical weeping’. Jane explained that the cervix changes consistency as it ripens; collagen and other substances transform within the cervix, allowing the cervix to soften and stretch. These changes cause the cervix to lose a watery fluid in the weeks and days before labour, from about 35 weeks gestation onwards. Not everyone notices this weeping – perhaps some fluid will be lost into the toilet – while other women will observe a distinct increase in watery vaginal secretions and dampness. It can be a bit disconcerting to leak fluid in this way but this fluid secretion is not usually confused with amniotic fluid if the midwife takes a careful history and, in partnership with the woman, examines the fluid. If there is a doubt, a gentle examination (if the woman wishes) with a sterile speculum could be helpful, but this is often not necessary if a careful history is taken.

SCENARIO THREE: HINDWATER RUPTURE?

There is a third and very common scenario. A typical situation might be that there seems to be a fairly obvious rupture of membranes. A pad is soaked, or two pads, with no surges (contractions). There is more fluid than would be experienced with cervical weeping alone and there is an initial gush, but labour doesn’t usually start. Then, over the next day or so, the fluid trickle slows or even stops. Sometimes there is still minor trickling after the initial flow. The woman is recommended by her midwife or obstetrician to have an augmentation (induction) of labour after 24 hours if the labour hasn’t started by itself. As part of the induction process, a vaginal examination is conducted. If the cervix is dilated (open) enough, it is possible to feel the sac (bag) of fluid bulging through the opening. It feels like a balloon full of water. It is usually possible to feel the harder shape of the baby’s head lying behind the balloon.

It seems odd if there has been a rupture of the membranes that the bag of membranes should be bulging, but the midwife or obstetrician has an explanation. The woman is told that she must have had a ‘hindwater rupture’. The explanation is that the membranes have sustained a rupture in a part of the balloon-like sac behind the head. The head acts as a plug so only small amounts of fluid escape at a time. The membranes that bulge in front of the baby’s head are described as the ‘forewaters’. As part of the induction process the midwife or obstetrician uses an amnihook (like a crochet hook) to make a hole in the membranes (this is known as amniotomy). The waters often flow out in copious amounts at this point and the balloon-like sac seems to deflate. Usually this brings the baby’s head down onto the cervix and often stimulates surges (contractions) within a few hours.

This description of what has happened is told to women as if the hindwater/forewater description is a fact. However it is actually a theory rather than a fact. However, the idea of a hindwater rupture has come to me to seem far-fetched, and I’ve come to believe that another explanation may be more likely in many cases.

I consider it more likely that a so-called hindwater rupture is actually a rupture of the chorion, while the amnion remains intact. I need to explain a bit more about the anatomy of the amniotic sac in order to describe what I mean.

SCENARIO FOUR: CHORION RUPTURE LEAVING THE AMNION INTACT

The baby lies within a balloon-like structure known as the amniotic sac which is filled with fluid called amniotic fluid, commonly known as the waters. The walls of the sac consist of two membranes with the outer membrane of the sac being called the ‘chorion’ while the inner membrane is called the amnion. It is the amnion layer that produces the amniotic fluid in which the baby floats and swims. (See http://www.pregmed.org/amniotic-sac.htm for more details.)

I came to this understanding of the possibility of chorion rupture a few years ago when I cared for a woman who had a supposed ‘hindwater’ rupture. She had a fairly substantial flow of clear fluid which soaked a pad or two but which then diminished. We did not test the fluid that was escaping – there seemed to be a good history of a spontaneous rupture of membranes or SRM. The woman wanted to await labour at home rather than having a hospital induction/augmentation of labour. Over the next few days, labour did not begin, and the flow of fluid virtually stopped. The mother monitored herself carefully for signs of infection and there was no infection. After days of waiting, I undertook a vaginal examination (not recommended unless absolutely necessary if it is suspected the membranes have ruptured) and I felt the taut bulging membranes which were positively bulging with fluid. I could feel quite clearly that there seemed to be hole in the chorion – I could feel an edge to the ‘hole’ which could be moved (the chorion slipping over the amnion). It was obvious that the chorion had ruptured, but the amnion was intact.

At the mother’s request I proceeded to carry out an artificial rupture of membranes (ARM), which was one of the very few occasions in my career as an independent midwife I have performed an ARM. There was a very substantial flood of fluid and the baby was safely born at home very quickly afterwards.

I had never heard of such a thing as a chorion-only rupture, but at the time I undertook a literature search and came across a single abstract by J S Cohain (see https://www.ncbi.nlm.nih.gov/pubmed/25279443) which describes this phenomenon as ‘false’ rupture of membranes.

Though there have been few articles published about the clinical implications of chorion rupture, and the phenomenon does not seem to be widely acknowledged in practice, there are articles published in peer-reviewed scientific journals such as ‘Placenta Reprod. Med.’ which discuss in detail the characteristics of the amnion and chorion. Much more is known in the scientific community about the role of the placenta and membranes than appears to have filtered into clinical practice. This 2023 article titled The Role of Fetal Membranes during Gestation, at Term , and Preterm Labor by Truong, Menon and Richardon explains in more detail about the anatomy and physiology of the membranes. Fascinating!

Update 2nd October 2024: Since I first published this blog back in (I think) 2020, I was fortunate to have had a conversation with Anne Frye who is the midwife author of what I would describe as the most important midwifery textbooks of our time, Holistic Midwifery Volumes 1 and 2. Anne told me that she described chorion rupture in Volume 1 of Holistic Midwifery. This reference can be found on page 860. Anne Frye suggests that ‘those leaks which are typically termed ‘high’ that reseal are usually due to the chorion breaking while the amnion remains intact’. In conversation with Anne, she too described feeling the intact amnion and the edges of a breach in the chorion.

HINDWATER RUPTURE OR CHORION RUPTURE: DOES IT REALLY MATTER?

It does matter, because if there has been a true rupture of both chorion and amnion, this means there is a breach in the sac surrounding the baby which could potentially allow bacteria to enter the fluid directly around the baby. This fluid is intended to be sterile until the baby is born in order to protect the baby from infection because the baby does not have a developed immune system of its own until many weeks after it is born (though baby does have some secondary immunity from the mother). In theory there would be less chance of infection if the amnion is intact, though as both amnion and chorion play a part in protection against infection, protection may be weakened even with a chorion-only rupture.

The more I think about it, the more I question the logic behind Scenario Three – the standard hindwater rupture. It is supposed that a small hole occurs in the membrane behind the baby’s head and the baby’s head acts like a cork. But actually, the baby’s head isn’t a cork – it doesn’t fit totally snugly. Why, after the initial flow of fluid, is there so little? If there was a breach of the sac wouldn’t you expect a steady stream – water doesn’t need a big space through which to leak? And when the supposed ‘forewaters’ do eventually rupture, whether artificially or naturally, there are often copious quantities of fluid – far more than would be expected from these forewaters which are supposed to be just an inch or so of fluid filled structure. Why is there so much fluid at this stage if there has previously been a true rupture of both membranes?

Doesn’t it seem more likely that the chorion has ruptured, which allows a relatively small amount of clear fluid to release at the time of rupture, but which then almost stops leaking?

IS IT POSSIBLE THAT THERE IS NO SUCH THING AS A HINDWATER RUPTURE?

Could hindwater rupture fall into the category of medical myths which seem self-evident at the time, but which later generations view as laughably naive? If my theory is correct and most cases of hindwater rupture are in fact chorion ruptures, then the amnion is still intact for most mothers and babies and it follows that there is less likelihood of bacteria entering the amniotic fluid. Where there is any doubt, careful monitoring for infection would be wise, but there would be little indication for immediate augmentation (induction) of labour.

I would be very grateful if you could comment to let me know your experiences.