Madness is a complication of childbirth. This graph is from a Scandinavian Paper about first time mothers. One can easily see that there is quite a high rate in the first few months. This rapidly decreases towards the usual incidence of madness, which is about one person per 1000 a year in the young.

For women, childbirth, not having children, is a risk period. But there are risks for this.

If you allow for previous psychiatric illness — the big hazard ratio is not being with your partner at the time of birth.

I’d speculate this reflects the common sense of most traditional societies; women with small babies need their family and relatives around to support them through the first few weeks.