No, my personal 'cut off' age was 35, but I had my first at 27, second at 34 and my third at 35. I have to say though my first pregnancy was the hardest, although having SPD with the others was painful and made looking after the child/children I had trickier.
It's a more difficult choice for you if you had your first at 40, but I think if I was you and had had my first at 40 and wanted another I would have had them closer together and had another one before now.
I am 46 now and my youngest is 11 and I cannot imagine having another at my age, I'm starting to get the usual aches and pains that seem to start in your 40's and I would find it very hard to get down on the floor to play with a baby/toddler and run around after them nowadays.
I had school friends with older parents and now they are my age they have mostly lost their parents and their parents always seemed to be a bit out of touch when my friends were younger.
I think it's unfair to knowingly increase the risk of leaving your children without parents/having to care for elderly parents when they are likely to need your support/have their own young families to manage too.
The risks to you during and after pregnancy are higher as well I believe as you get older, and to the baby. There's no guarantee that any pregnancy will result in a healthy child, but the odds decrease as you age.
How would you, your DH and your existing dc cope with a severely disabled child? It would take attention and time away from your current dc, is extremely stressful, it affects your ability to work and may lead to a need to lifelong care for another dc, together with the extra worry of who would look after them once you and DH were no longer here
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I would focus on enjoying the dc you have and the fact that there is so much you can do more easily with one than with multiple children. It is hard coming to terms with the fact that you may not have another child but there are positives for you, your DH and your dc
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