Amniotic fluid is a clear, slightly yellowish liquid that surrounds the foetus during pregnancy. It is contained in the amniotic sac. The purpose of the amniotic sac is to protect the foetus from infection to cushion the foetus in the womb, a medium for foetus to grow in and thrive by maintaining a constant temperature, allowing movement to aid muscle development, protecting against infection – the membranes provide a barrier- the fluid contains antimicrobial peptides, assisting lung development, baby breathes fluid in and out of the lungs, and also plays an important part in developing many of the baby’s vital internal organs, such as the lungs, kidneys and gut.
At full term, there is between 500-1000 ml of amniotic fluid. This is mostly made up of amniotic fluid secreted by the amniotic sac (the membranes). The baby also contributes urine and respiratory tract secretions into the fluid. The amniotic fluid is constantly being produced and renewed – Baby swallows the fluid; it is passed through the gut into the baby’s circulation; then sent out through the placenta. This process continues even if the amniotic membranes have broken. The amniotic fluid contains substances such as albumin, urea, uric acid, creatinine, lecithin, sphingomyelin, bilirubin, fat, fructose, leukocytes, proteins, epithelial cells, enzymes, vernix and lanugo.
Unfortunately artificial rupture of membranes (AROM)has become “routine practice”. It is useful if there is delay in progress. But it really has no place in normally progressing labour. Very often the membranes will rupture just before birth. In the animal kingdom the offspring are very often born in their amniotic sacs. The research indicated that it does not shorten labour by any significant amount. It is a method of inducing labour but that is another story. In my experience, AROM usually benefits the midwife or obstetrician. It speeds things up for them, and also gives them peace of mind as they can see whether or not there is meconium in the liquor so they can get a paediatrician ready to be present at delivery. There is no indication for it in normal labour.
I was at a workshop many years ago where a midwife was giving a talk about home birth and leaving the membranes intact. After the lecture, one of the attendees was horrified that a midwife would not perform AROM as it was so dangerous not to know if there was meconium! She definitely needed a chat! Then there was the OB/GYN who commented on labour ward protocols: ” there is no reason to keep membranes intact even in a labour that is going “normally,” all membranes should be ruptured because they serve no pupose at all.” Of course the fact that most women report more pain is neither here nor there, because there’s probably no randomised control trial that proves it! That means mother nature has got it horribly wrong for the last 100,000 years and you’ve managed to figured it out completely in the last 100 years!
But it is not only the providers that can be the problem, birthing mothers can be just as uninformed. I have frequently had multiparous women request AROM for relief of pressure and I often find they tend to progress very quickly post AROM – tends to bring the head down onto the cervix and enhance uterine contractions. However, a cochrane review of the available research states that “the evidence showed no shortening of the length of first stage of labour and a possible increase in caesarean section. Routine amniotomy is not recommended for normally progressing labours or in labours which have become prolonged.”
Gabbe, S. G., Simpson, J. L, Niebyl, J. R. Galan, H., Goetzl, L. Jauniaux, E. R. M. Landon, M. (2007). Obstetrics: Normal and Problem Pregnancies. 5th ed. Philadelphia, PA: Elsevier Churchill Livingstone.
Smyth, R., Alldred, S. K., Markham, C. (2007). Amniotomy for shortening spontaneous labour. Cochrane Database of Systematic Reviews. Issue 4. Art. No.: CD006167.