<unk><unk>  is affected by<unk>  and is a major<unk>  factor for women. A woman's<unk>  peaks between the late teens and late-20s, after which it starts to decline slowly. While many sources suggest a more dramatic drop at around 35, this is unclear since few studies have been conducted since the nineteenth century. One 2004 study of European women found<unk>  of the 27–34 and the 35–39 groups had only a four-percent difference. At<unk>  45, a woman starting to try to conceive will have no live birth in 50–80 percent of cases. Menopause, or the cessation of menstrual periods, generally occurs in the 40s and 50s and marks the cessation of<unk> , although<unk> -related infertility can occur before then. The relationship between<unk>  is sometimes referred to as a woman's "biological clock."
Age and female fertility
Obesity and fertility
Smoking and pregnancy
Women and smoking
Risk factors for breast cancer
Signs and symptoms of pregnancy
Diabetes and pregnancy
Gravidity and parity