My periods are super irregular. With both of mine I was able to work out my EDD based on when I thought I would have conceived/when I got a positive test (and was correct within a handful of days) but I’m a midwife and am fairly in tune with my cycles in terms of symptoms of ovulation etc. Both times I literally woke up and was like ‘I’m definitely pregnant and should take a test’ at about 3.5 weeks (which was before my period would have been due if I was in any way regular). However, my EDDs based off my LMP were 6-8 weeks off.
I’ve often met women who genuinely had no idea they were pregnant until fairly late on, or who contact us with no idea when their last period was. When you aren’t planning a pregnancy it’s easy not to keep track, especially when you are on what you think is reliable contraception!
However, just in my opinion (and with the benefit of professional experience), I think this pregnancy may have been at least semi-planned, if not consciously, then unconsciously longed for. When women have children removed, it is very common to keep having babies in the hope that eventually you will be allowed to ‘have another go’ or ‘start fresh’.
I absolutely can’t say that this was the case with CM of course, but it’s a startlingly common occurrence.