Category Archives: My reproductive system

How and when does a pregnancy start?

When a single sperm fuses with an egg it is called fertilisation.1  Pregnancy starts several days after fertilisation.

Pregnancy does not begin until the fertilised egg has implanted in the womb, after having travelled through the fallopian tube.2

So if you’ve just had unprotected sex or contraceptive failure, no pregnancy will start until at least the sixth day.


Signs of pregnancy4

  • Late period
  • Feeling sick (nausea)
  • Being sick (vomiting)
  • Tiredness
  • Breast tenderness or soreness
  • Needing to pee (urinate) more often

If you think you might be pregnant, take a pregnancy test and/or visit your doctor. If you are pregnant it is too late for emergency contraception because it works to prevent the start of a pregnancy.



You can get pregnant at any time in your cycle

In theory, during the average woman’s menstrual cycle there are six days when sex can result in pregnancy. This conception risk period, also called ‘fertile window’ is the five days before egg release (ovulation), plus the day of egg release.1


You are at risk of conception if you have unprotected sex in the 5 days before ovulation because sperm can live for about 5 days, and can be waiting in the fallopian tubes, ready to fertilise your egg.2 An egg only lives for 24 hours.2

The highest risk of pregnancy is when ovulation happens shortly after unprotected sex

Sperm viability declines in the days after sex. This means that the risk of conception is highest when ovulation happens during the first three days following unprotected sex.3

When is this conception risk period?

You have no way of knowing when your fertile window is – and it can be at a different time every month.1


This means that you are at risk of pregnancy almost throughout the whole of your menstrual cycle.1

  • You might not ovulate on the same day of your cycle from one month to the other 1
  • Women with a regular cycle can be in their fertile window any time from day 6 to day 211
  • Women with an irregular cycle can be in their fertile window from day 8-281



  1. Wilcox AJ et al. BMJ 2000; 321: 1259-62.
  2. Pallone S and Bergus G. J Am Board Fam Med 2009; 22: 147–157.
  3. Wilcox AJ et al. N Engl J Med 1995; 333: 1517-21



Ovulation is the release of an egg from the ovaries.1 A woman is born with all her eggs. Once you start your periods, one egg (occasionally two) develops and is released during each menstrual cycle.2




After ovulation, the egg lives for approximately 24 hours3




Once the egg is released from the ovary it travels down the fallopian tube towards the womb. Fertilisation happens if a man’s sperm meets and fuses with the egg.1 Sperm can survive in the fallopian tubes for up to five days after sex.3




If the egg is not fertilised, the egg is reabsorbed into the body. Hormone levels fall, and the womb lining comes away and leaves the body as a period.1,2






A woman cannot get pregnant if ovulation does not occur.


1. Royal College of Obstetricians and Gynaecologists website. Medical terms explained. Available at Last accessed September 2013.

2. Aitken J et al. J. Clin. Invest 2008; 118 (4): 1330–1343.

3. Pallone S and Bergus G. J Am Board Fam Med 2009; 22: 147–157.

4. ellaOne® Summary of Product Characteristics.

5. World Health Organization. (In association with the International Consortium for Emergency Contraception, International Federation of Gynaecology and Obstetrics, International Planned Parenthood Federation, Department of Reproductive Health and Research). Fact sheet on the safety of levonorgestrel-alone emergency contraceptive pills. Available at: Accessed November 2013.

Understanding the menstrual cycle

The menstrual cycle is the process where an egg develops each month and the lining of your womb is prepared for possible pregnancy1

The menstrual cycle is driven by body chemicals called hormones. A cycle is counted from the first day of bleeding (your period) to the first day of your next period.2 The rise and fall of hormonal levels during this time control the menstrual cycle.

What’s happening in your womb?


What’s happening to your hormones?

The menstrual cycle is controlled by a complex interaction of hormones.1 In each cycle, increasing levels of hormones cause the ovary to develop an egg and release it (ovulation).2 The womb lining also starts to thicken.

What does it look like ?

The reproductive system, sometimes called the sexual organs, is the set of organs needed to make a baby, or reproduce.1

Your reproductive system is made up of a vulva, vagina, cervix, womb, fallopian tubes, ovaries and breasts. Unlike men, most of your reproductive system is located inside the body.1