Nearly every metric gets worse
- likelihood to get pregnant
- likelihood to bring child to term
- health risk to mother during pregnancy and child birth
- health risk to baby during pregnancy and child birth
- increased likelihood of multiple birth defects
- increased likelihood of genetic abnormalities
I'm not casting aspersions. My wife and I had kids when she was 38 and 40 respectively. But, the numbers for the risks are stark.
So even if it takes a year instead of one night to get pregnant, which wouldn't really affect long-scale statistics that much, more pregnancies fail, and more people may choose not to try at all because of the risks. That makes sense.