Several centuries ago, the early midwifery and OB books said that a baby born with thick meconium might be in trouble -- especialy if it was small, or if the labor had been difficult, or if the baby's heart had been slow or erractic during labor. If meconium is light -- what the old books called "coloured waters" - the baby rarely showed any effects. After all these centuries it seems we haven't added much new to this. We have made great progress in the last twenty years in TREATING babies with Meconium Aspiration Syndrom (MAS), and what about prevention? We've developed many new suctioning methods, but do they succesfully prevent MAS?
Here a large study out of Singapore confirming the old knowlege -- that Meconium Stained Amniotic FLuid (MSAF)is not uncommon, yet MAS is rare without the combination of thick meconium and poor Fetal Heart Tones. They found the incidence of MAS with light meconium staining was 0.3%, with moderate it was 5.8%,and thick was 61% -- and that poor heart-tones were a deciding factor. This study had nearly 2000 MSAF babies, and that 3out of a thousand number (for light mec) is rather reasuring, considering the incidence of meconium staining reportedly ranges from about 15% to 28%.
That "range" is interesting, and some study locations report a much higher range than others. Just annecdotally, most midwives see a much lower incidence of MSAF (of course we deal primarily with low risk pregnancies), but many of us have wondered if the rate is increasing. Seems it just might be according to this large 1991 hospital study which concluded "the incidence of meconium-stained amniotic fluid increased 40.9% over the study period, from 18.8% in 1980 to 26.5% in 1986". They give no guess of "Why".....but i personally wonder if the advent of EFM (with supine maternal position) and epidurals might be a factor. Or maybe the rise in rate of induction? Or augmentation? It wasn't all THAT many years ago that pitocin was a rarely used drug -- now it's almost a routine thing.
But, what should we do if MSAF occurs (assuming heart tones are reasuring)? Do we suction? And when? On the perinuem? After delivery, but before the first breath? ANd what do we use if we ARE going to suction? Some midwives are criticised if they use an old-fashioned bulb syrnge instead of a delee suction tube. Is a delee trap any better -- more effective -- than a bulb syrnge or suction tube? The DeLee was adopted without good study. It turns out that a bulb syrnge is probably BETTER than a DeLee, and this study concludes "We recommend the use of bulb suction as routine obstetric practice even in the presence of thick meconium." This one also calls a bulb syrnge the "preferable method" since it is as effective, less expensive, easier to use and safer, than a DeLee.
But does it make any difference if we suction, or when, or with which device? Here is one of many large studies concluding that MAS develops long before we ever see the baby:
"oronasopharyngeal DeLee suctioning at the perineum does not affect the rate of meconium aspiration syndrome. We speculate that meconium aspiration syndrome is predominantly an intrauterine event associated with fetal distress and that meconium in the airways is merely a "marker" of previous fetal hypoxia."
Meconium Aspiration is non-preventable. No matter who attends the birth, no matter where the baby is born and no matter which suctioning method (if any)is used. It occurs within the womb, not on the perineum. It is not predictable. Our only clue may be an poor heart rate pattern. In effect, our oldest textbooks are still accurate. We've made progress is "treating" MAS, but not in "preventing" it.