because the average age of those who conceive and carry has increased)))))
Nowadays, few people think about a child under 25, rather closer to 30-35.
For me, the reason is hormonal contraceptives. Such things do not pass by for a woman's body. This is if we exclude third-party factors: age, stress, lack of sleep, chronic and not only diseases, etc. Living conditions also significantly affect the quality of food, ecology.
This statement is true only among certain groups of the population.
On the one hand, the likelihood of conceiving and bearing a child is expected to decrease with age, with a toxic load on parents, in connection with past diseases (including infections transmitted sexually), a history of abortion. An increased information load and disturbances in the circadian rhythms of sleep and wakefulness also play a significant role. It should also be borne in mind that modern methods of contraception effectively contribute to the prevention of conception, and a change in the norms of sexual behavior in society contributes to a sharp increase in STIs.
On the other hand, the relatively recent advances in modern medicine have led to a change in the driving factor of natural selection, and those who, half a century ago, were not destined by nature, were able to get pregnant and give birth. In such conditions, the reproductive health of certain groups of the population is constantly changing.
Why has it dropped? It's just that women began to give birth less and protect themselves more. In the Middle Ages, the average woman had about 5+ children, but keep in mind that the mortality rate was catastrophic, most did not live up to 2 years. Now women are more planning a family and rely on quality rather than quantity.
Although it is difficult to say that the probability of conception has fallen, given that in just a little less than 200 years the Earth's population has grown 7 times