Each hospital will have different policies on when waterbirth will not be recommended. Generally, a woman who needs continuous monitoring of the baby's heart beat will not be able to labour or birth in water, because most of the monitors are not waterproof. Fortunately, at the hospital where I attend births, we do have water-proof monitors so women can have a waterbirth with a VBAC, for example. Certain complications during labour may require a water birth to be abandoned for safety reasons. This might be bleeding, fetal distress, excessively prolonged labour, high blood pressure, shoulder dystocia and premature birth.
Water birth can slow down the progress of labour in some cases, especially if the woman is less than 5cm dilated when she enters the pool. If this is the case, simply exit the pool and re-enter when labour is further established.
It is perfectly safe to birth the placenta in the pool, however you can expect your midwife to assist you out of the pool if your blood loss is thought to be excessive.
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