The Reactive Uterus orthe BirthDay BalloonhgfedcbaZYXWVUTSRQPONMLKJIHGFEDCBA Margaret Jowitt IT'S ARM's 21stbirthday and so this seems an appropriate time to air another theory that has escaped the textbooks. Before writing a book intended tobe mainly about home birth, I thought I really ought to learn about how the uterus works in labour. To my surprise there was very little infor- mation. Learned tome after learned tome outlined the three stages of labour telling the reader what happens but nowhere did it say how. Anatomy and physiology sections were full of information about structure and there were snip- pets of useful information such as the standard description of longitudinal muscle contracting and retracting to pull up the cervix, but the uterus was never seen as a coherent whole. What is responsible for contractions coming in waves? Why do contrac- tions get stronger and closer together during labour? I was left with the impression that for the professionals, just like women in labour, contrac- tionsjust 'happen'. They knew what contractions did, but they didn't know how and why. Most textbooks deal only with treatment for 'inefficient/ malfunctioning/lazy' uteri, and that treatment is based on pragmatism rather than science, which could be described as the sledgehammer approach. Perhaps if we knew more about the natural function and what disrupts it we would need less recourse to unphysiological amounts of oxytocin, to forceps and to the scalpel. I think that ifwe know what is happening, how and why, then we can accept contractions gladly and cope with labour better. People caring for labouring women will have a better idea what is likely to impair uterine function and what will facilitate it. Ihad to delve deeper and deeper into the physi- ology literature to discover how the uterus works in labour and I ended up with a radically different view of the labouring uterus. I learned that it should not be looked at as an isolated organ, but as a dynamic and reactive part of a triad consisting of the mother's mind, her whole body and the physi- cal activity of her baby. All three work together as a united whole to allow the baby to be eased gently into the world. Beforelooking more closely at these three effects upon the uterus in labour, it would be helpful to know more about its mode of action. And I shall start by changing your thinking about it and mak- ing it more 'user friendly'. Let's forget the anatomy and physiology for the moment and look at the mechanical properties of the muscle of the uterus. Physics may not be your strong subject (to tell you the truth it wasn't mine either) but fortunately that doesn't matter because there is a simple illustration that anyone could understand: The Womb's a Balloon • It's a hollow elastic bag • It's about the same size • It's flat with touching sides when empty and pear-shaped when 'blown up' (gravid) • If it is stretched it will revert to its original shape - it has elastic memory. (Imagine putting your fist against a blown-up balloon, then withdrawing it, the balloon regains its pear shape - you do this from the outside but the baby will do it from the inside.) The uterus is more dynamic than a bal- loon; during labour myometrial cells react to being stretched by becoming even smaller - contraction leads to retraction. • It can expand to many times its original size and then revert to near its previous size; deflated balloons never quite retain their virgin state, neither does the uterus. • It can be under enormous pressure and yet not burst • It can be tied shut (quite literally with a Sirodhka stitch) • Up to a certain point it can cope with slight flaws in its substance, e.g. scar tissue from a caesar- ean section -but you can never quite tell • It is fragile yet immensely strong • If maltreated it can burst KJIHGFEDCBA and last but not least... • Something usually used to celebrate life can lead to tears or tears The womb is not just a passive elastic bag to be manipulated from the outside, it can generate more of itself; it grows from 2 oz to 2 lb during preg- nancy and then within six weeks of birth it digests itself to go back to its pregravid self (autolysis). It is not an inert, passive elastic bag floating aimlessly in the air but it is dynamic and actively responds to many and various forms of stimulation. The Dynamic Cervix Like the main body of the uterus, the cervix is also made of elastic smooth muscle, but it has an added matrix of collagen and connective tissue which is generated upon instructions from hor- mones. This makes it stretch resistent during 14 Midwifery Matters ISSUE 74 Autumn 1997