From a biological perspective, the peak ages for a woman to have a baby are between 18 and 20. Women’s fertility actually starts to decline in the late twenties, men’s after age 35, according to a 2002 study in Human Reproduction. Researchers from the United States and Italy studied 782 healthy couples and estimated the chances of pregnancy following intercourse two days prior to ovulation, the peak time for conception. Women ages 19 to 26 whose partner was the same age had about a 50 percent chance of pregnancy in any one menstrual cycle. This fell to 40 percent for women 27 to 34, and less than 30 percent for women 35 to 39, unless their partner was 5 years older, at which point the pregnancy rate dropped to 20 percent. The good news: this did not mean a lower overall chance of achieving pregnancy if women delayed trying until their late twenties or early thirties, the researchers noted. It meant that it may take women in their late twenties a month or two longer to become pregnant than it would have earlier in that decade.