Understanding how fertility works

Content Fertility and the female body

Women are most fertile in their 20s, with fertility declining over time. Each month, a healthy woman’s chance of pregnancy is: 

Age and Chances Graphic


Although conception may be more difficult with age, pregnancy is still possible for many women. Understanding how the fertility cycle works can help improve your chances of becoming pregnant. Read on for a refresher on the female reproductive system, menstrual cycle, and the male’s role in conception.

Understanding the female reproductive system

Fertility Cycle Graphic

The menstrual cycle, explained

The female menstrual cycle typically lasts between 28 to 32 days and can be divided into 3 phases. Each phase helps prepare a woman’s body for possible pregnancy.

Endometrial Cycle
Stage 1: Follicular phase
  • The endometrium starts to shed and a period begins
  • A gland inside the head, called the hypothalamus, releases gonadotropin-releasing hormone (GnRH)
  • The ovaries mature several eggs inside their follicles with the help of 2 other hormones: follicle stimulating hormone (FSH) and lutenizing hormone (LH)
Stage 2: Ovulatory Phase
  • Ovulation varies from person to person, but happens at or around day 14
  • For it to occur, the pituitary gland releases a large amount of LH at once
  • This causes the fastest-growing follicle to rupture and release a mature egg into the fallopian tube
Stage 3: Luteal phase
  • The mature egg can potentially be fertilized during this stage as it moves through the fallopian tube
  • While this happens, the empty follicle left behind in the ovary starts to release the hormone progesterone
  • This helps nourish and thicken the endometrium to prepare it should an embryo implant
  • If implantation happens, the body produces human chorionic gonadotropin, or hCG, which tells the body it’s pregnant
  • If fertilization does not happen, a period will occur as usual

5 facts about the male reproductive system

Male Sex Cells Icon

Fact #1: Sperm are the male reproductive sex cells

Sperm are produced in the testes and mature throughout the reproductive tract in about 64 days.  

Sperm Icon

Fact #2: Sperm store DNA in structures called chromosomes

Sperm are shaped like tadpoles. The head of the sperm stores the DNA and the tail helps it reach the woman’s egg.

Seminal Vesicles Icons

Fact #3: The seminal vesicles also help

They produce a sugar-rich fluid that gives the sperm energy to swim. This fluid makes up much of the semen.

Fertilization Icon

Fact #4: Only one sperm is needed for fertilization

There are millions of sperm inside every ejaculate, although only one is needed for fertilization. Ejaculated sperm can survive for 3 to 5 days inside a woman’s uterus. 

Chromosomes Icon

Fact #5: The sperm and egg each contain their own set of 23 chromosomes

When the sperm fertilizes the egg and conception happens, these 46 chromosomes combine to form 23 pairs of unique chromosomes that are made up of each parent’s genetic information. This is called an embryo.