Expecting less is not the lesson
No study has ever tested lowering women's expectations, and everything that has been tested points the other way.
The obvious moral of a birth that went wrong is that you should have expected less. It is the moral almost everyone offers, gently, and it is not supported by anything.
The question has been studied directly. A systematic review pulled together eleven prospective studies from nine countries that measured what women expected beforehand and what they experienced, then followed them. Here is what it found. A gap between expectation and experience was consistently linked to lower satisfaction with the birth. It probably raises the risk of post-traumatic stress symptoms, though every study that found that also found other predictors of equal or greater weight. And it was not consistently linked to postnatal depression, or to later fear of childbirth. There was not enough data to combine the studies into a single figure.
Where a size was reported at all, it was small. In the one study that reported the correlation directly, the link between a birth going differently from plan and overall satisfaction was 0.13, which accounts for under two per cent of the difference between women. More interesting is what carried that small effect: guilt during the birth, and how the woman perceived the care she got. In other words, it was not the deviation that did the damage so much as how the deviation was handled, and what she was left believing about herself.
And note what nobody has ever done. No trial has tested telling women to expect less, and no study shows that women with low expectations look back on birth more happily. The consistent finding runs the other way: expectations being met predicts satisfaction.
WHO's own definition of a good birth is worth quoting in full, because it is the opposite of expecting less:
Women want a positive childbirth experience that fulfils or exceeds their prior personal and sociocultural beliefs and expectations. This includes giving birth to a healthy baby in a clinically and psychologically safe environment with continuity of practical and emotional support from birth companion(s) and kind, technically competent clinical staff. Most women want a physiological labour and birth, and to have a sense of personal achievement and control through involvement in decision-making, even when medical interventions are needed or wanted.
Read the last clause twice. WHO builds a positive birth experience that survives intervention. A birth that needed help is not a birth that failed, and neither are you for having wanted it to go otherwise.
"I am not going to want less. I am going to ask for it differently."