Caldeyro-Barcia’s (1979) studies showed what most midwives practice or believe intuitively; that coached pushing and prolonged breath holding by the woman during the pushing stage of labor is dangerous to the baby. He showed that this type of pushing caused placental perfusion issues (not enough blood flowing between baby and placenta) and resulted in fetal hypoxia. Aldrich, et. al (1995) showed that prolonged breath-holding decreased fetal cerebral oxygenation. Thompson’s 1993 study showed that women who had coached pushing for more than an hour, the babies had a lower pH at birth (meaning they were acidotic and likely stressed).
Basically, there is no evidence to support coached pushing but it still exists! Observational studies have shown the following complications that arise from coached pushing; maternal exhaustion, more assisted vaginal births, more episiotomies and tears, more impact on the pelvic floor and instances of urinary incontinence after birth.
Watching a woman’s body push her baby out is an education in these principles. I have observed that she will naturally breathe faster and slower as she needs to; she will grunt and hold her breath for short amounts of times, as she needs to. I would never pretend to understand exactly what is going on in her body to prompt her to do what she is doing. If she is unmedicated and allowed to follow her body’s lead, I think there is little that can go wrong. The most physiological way to push a baby out is with the body’s own cues. Some women will experience the “fetal ejection reflex” which can look like there is next to no “pushing”. It is a physiological expulsion of the baby by the body. When you’ve seen this happen, it is a world of difference between the forced/coached hospital (or home birth!) pushing that can turn women blue in the face.
So, despite what you have heard...there is no good reason (physiologically or otherwise) to think that anyone should tell you WHEN or HOW to push. You will know when it is time. You will do it just right, and with the greatest benefit to you and your baby and with the least amount of trauma.