The average age of first-time mothers has been rising over time. Years ago, it was commonplace for women to have children in their twenties and early thirties. But current lifestyles, and other competing interests, have pushed the average age of first-time mothers beyond the mid-thirties and into the forties.
The consequent effect is lower spontaneous conception rates and an increasing demand for assisted conception services. Spontaneous conception is mostly dependent on the female age. Younger women have many good-quality eggs. Their chance of conception month to month is therefore higher.