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.
Kids is fast.
- Stress on the relationship of trying and failing for a long time - Stress of fertility treatments, if needed - Likelihood of dealing with inevitable miscarriages on the way to a birth - Overall "medicalization" of pregnancy in middle age, and the stress of all that contact with the medical system
None of this touches on industrialization and higher education, which seem to be the more universal effects, even if one of their bigger effects is merely to delay motherhood.