Making babies is easy right? Take Part A, combine with Part B and the rest, as they say in the classics, happens naturally.

But what about if the “rest” isn’t happening naturally? Or maybe you’re just starting out and you’d like to understand a few of the finer points but you realise that you’ve forgotten most of what you learnt in high school biology about reproduction?

What Is Infertility?

Infertility is defined as the inability to conceive a child despite trying for 1 year. The condition affects about 9% of the reproductive age population.

To become pregnant, a couple must have intercourse during the woman’s fertile time of the month, which is right before and during ovulation. Because it is tough to pinpoint the exact day of ovulation, having intercourse every other day during this time maximizes the chances of conception.

After a year of frequent intercourse without contraception that does not result in pregnancy, a couple should go to a health-care professional for an evaluation. In some cases, it makes sense to seek help for fertility problems even before a year is up.

A woman over age 30 may wish to get an evaluation before 1 year. At age 30, a woman begins a slow decline in her ability to get pregnant. The older she gets, the greater her chance of miscarriage. However, fertility does not take a big drop until around age 40. Despite a decrease in sperm production that begins after age 25, some men remain fertile into their 60s and 70s.

A couple may also seek earlier evaluation if:

  • The woman is not menstruating regularly, which may indicate an absence of ovulation that would make it impossible for her to conceive without medical help.
  • The woman has had three or more miscarriages (or the man had a previous partner who had had three or more miscarriages).
  • The woman or man has had certain infections that sometimes affect fertility (for example, pelvic infection in a woman, or mumps or prostate infection in a man).
  • The woman or man suspects there may be a fertility problem (if, for example, attempts at pregnancy failed in a previous relationship).

Conception Basics

First things first, if everything is going to plan then you each bring a very important ingredient to the equation. Women contribute an egg and men contribute sperm.


The first key fact to understand is that women are born with all of their eggs. That’s right, women are born with around two million eggs and by the time they hit puberty around 300,000 remain and that decline continues. Once a month, every month from puberty to menopause, women ovulate, releasing eggs in the middle of their monthly cycle. The whole process is controlled by two glands in the brain – the hypothalamus and pituitary – which tell hormones in your body to trigger certain physical responses. The egg is released from a mature follicle on the ovary (either ovary – it’s random) and travels down the fallopian tube. Fertilisation may occur in the fallopian tube if sperm are present. 

The egg survives for about 12 – 24 hours.


Men create sperm in the testes and they produce an average of 100 million sperm each and every day.  Over approximately three months, these sperm travel a system of tubes called the epididymis, maturing along the way before being released during ejaculation. Interestingly only around four per cent of sperm in an average ejaculation are considered normal & capable of fertilising an egg. After ejaculation, sperm are capable of fertilisation for about 72 hours. For some other cool sperm and male related facts, take a look at our Male fertility infographic. 


After the sperm are deposited into the upper vagina via ejaculation, they must travel through the cervical mucus into the uterus and then into the fallopian tube before they can meet with the egg.


Female and Male Reproductive Systems 

Sperm make this long journey under their own steam (and with some help from upward contractions of the uterine walls). During the trip, sperm prepare themselves to meet the egg by subtle alterations of their heads (acrosome) and movement patterns. When they meet the outer membrane of the egg, the sperm start to burrow through it and then enter the egg itself. At the moment the first sperm successfully penetrates the egg, a reaction is triggered that makes the egg resistant to all other sperm. This single sperm absorbs into the egg, where the genetic material contained in its head fuses with that of the egg. Fertilisation is now complete.


After fertilisation, the combined egg and sperm – now known as an embryo – develops in the fallopian tube for the first three days, then travels down into the uterus. By the fifth day it will become a blastocyst, a hollow ball of cells surrounding a cyst-like cavity. Once the blastocyst breaks free from its shell, or hatches, it is ready to adhere to the surface of the endometrium.

You might be surprised to know that the average fertile couple in their 20s, having regular, unprotected sex, has just a 20 per cent chance of this happening naturally each month. You are at your most fertile around 22-23 years.