For mammals, such as lions, tigers and giraffes. Their reproductive mode is in vivo fertilization, that is, sperm and eggs are fertilized in the mother. The estrus of these animals is usually very short, and females will show obvious courtship behavior to attract males during estrus. Male animals will mate after sensing the ovulation period of female animals, allowing sperm to combine with eggs, leading to pregnancy.
In contrast, humans are conceived through sexual intercourse, but one sexual intercourse is not enough to lead to immediate pregnancy. This is because the human reproductive process is more complicated. Women's menstrual cycle is usually about 28 days, and ovulation occurs in the middle of the menstrual cycle, about 14- 16 days after menstruation begins. Only sexual intercourse during ovulation can lead to pregnancy. In addition, human sperm need to swim in women for a period of time to reach the egg, which also increases the difficulty of conception.
In addition, humans have other defense mechanisms to avoid excessive pregnancy. For example, a woman's body will prevent sperm fertilization during anovulation, and a woman's immune system will attack foreign sperm.
To sum up, mammals are more likely to get pregnant after mating, while humans need to have sexual intercourse at a specific time to increase the possibility of pregnancy.