Understanding the menstrual cycle and hormone-based contraceptives

Hormonal management of contraception is built on the knowledge of hormonal changes during a menstrual cycle. Each cycle is typically 28 days on average, and can be divided into the follicular phase, the ovulation day and the luteal phase. At each stage, the balance between gonadotrophin-releasing hormones and sex hormones is dynamically tuned.

The gonadotrophins include follicle stimulating hormone (HSH) and luteinising hormone (LH), which are secreted by the anterior pituitary in the brain. The sex hormones include estrogen, progesterone and androgens, which are secreted by the ovaries.

In the first two weeks of a cycle, termed as “pre-ovulation” or “follicular phase”, follicles enlarge in size under the influence of FSH. By day 6, one follicle out of the growing pool becomes the dominant follicle, which encompasses the oocyte to be ovulated.

At the same time, estrogen production from the dominant follicle leads to a surge of LH, which ultimately results in ovulation, typically on day 14 in a textbook-like cycle. However, more than half of the women will ovulate outside days 12-16 of their menstrual cycle. This is due to variable length of the follicular phase, which can range from 6 to 16 days.

After ovulation, the follicular remnants form a corpus luteum that produces progesterone. This inhibits FSH and LH production as well as supporting the released oocyte. Together with the high estrogen produced by the ovaries, progesterone and estrogen cause the lining of the uterus to thicken, preparing for a possible implantation.

Once ovulated, the egg can survive for 24 hours, while the sperm survives 48 to 72 hours. Therefore, pregnancy is likely to occur in the 72 hours window before ovulation until 24 hours after ovulation.

If no sperm is around to fertilise during this time, the corpus luteum degenerates, resulting in the decline of progesterone. At the same time, estrogen level also decreases, causing the top layers of the uterine lining to shed, which is when the menstrual bleeding occurs.

Combined oral contraceptives

Accidental pregnancies occur much less frequently nowadays thanks to various contraceptive methods. It is estimated that contraceptive use in Australia is above 70%. Among them, the most popular female contraceptive in the “pill”, a combined estrogen and progesterone therapy that was first approved by the FDA in 1960.

The combined oral contraceptive (COC) typically involves 21 active tablets of combined estrogen and progestogen preparation. This method is estimated to be up to 93-99% effective, meaning that if 100 women use it correctly, one will become accidentally pregnant in one year. However in real life where incompliance and incorrect usage are taken into account, about 9 women in 100 can become pregnant in a year.

COCs work by suppressing ovulation and preventing implantation. Progestogens mimic natural progesterone but have a longer half-life. They act to inhibit LH and produce a thick cervical mucus that hinder sperm entry into the uterus.

How to use COC?

COC should be commenced on the first day of your menstrual bleed or within the first five days of the menstrual cycle, when the contraceptive activity is immediate. However, if you commence the first active tablet after a period, 7 days of other forms of contraception are needed. Be sure to check with your pharmacist or doctor when exactly you will be covered by the pill.

There are some circumstances where the pill may not work, such as after vomiting or diarrhoea. Some medicines such as anti-epileptic drugs may also prevent the pill from working, which you can check with your doctor or pharmacist.

If you missed taking your pill, you may also be at risk of becoming pregnant and should consider using another form of contraception such as condoms until the next period arrives. During the 24 hours after missing a pill, you can still take it as soon as possible and then take the next one at the usual time. You will be protected against pregnancy in this case, but not when it’s been 48 hours since your last pill.

Most brands of COCs come with sugar pills that are meant to induce a “period”, although cyclic bleeding is not essential. You can skip a period by continuing to take the hormone pills instead of sugar pills. In fact, tricycling is a practice where women continuously use the hormonal pills for nine weeks before allowing a period. It has been reported to improve heavy, irregular or painful bleeding, acne, and anaemia.

Are there side effects with COC?

There are rarely any serious health problems caused by COC, but the most dangerous is blood clots. More common side effects can include:

  • breakthrough bleeding
  • nausea
  • breast tenderness
  • headache
  • lower libido
  • weight gain

Estrogens have the potential to affect blood clotting and increase the risk of a condition called venous thromboembolism. They may also increase blood pressure and mildly worsen glucose tolerance.

The relationship between COC use and cancer is mixed. While the risk of estrogen-associated breast, cervical and liver cancer is elevated, we also know that estrogen is protective against endometrial cancer with greater than five years of use. COC users also have lower rates of death from cancer, cardiovascular disease and other diseases.

Lastly, please note that COC is not the only contraceptive method out there and it may not be fore you. Tune in for our next blog on the other contraception choices!

Contraception choices other than the pill

Most women are familiar with the pill, which relies on altering the hormonal levels to prevent pregnancy. But you may not like the idea of having to remember it every single day, or that it seems to lower your libido. The pill may not be for you, and you can explore other options!

Natural family planning

Some couples prefer not to use any substances that affect their body or the sexual experience. Natural family planning is based on observing body changes that indicate where the woman is in her cycle and avoiding the presumptive fertile window. These include cervical mucus changes, temperature shifts and past cycle length.

This strategy may work well for women who have a textbook like cycle every month and therefore is reasonably predictable. However, the majority of women have irregular periods or one that varies each month. Because body changes are perceived by the observer, it may not be necessarily accurate. Depending on the couple’s compliance and judgement, natural family planning may be 76-99% effective.

Barrier methods

Barrier methods physically prevent the meeting of the sperm and the egg. The most well-known barrier contraceptive is the condom. It is also the only form of contraception that protects against many sextually transmitted diseases. However, condoms may tear or fall off when not used correctly. When used correctly, condoms are about 98% effective. Note that some people may be allergic to latex condoms.

The diaphragm is a similar barrier method, but instead of putting it on the male penis, it is placed inside the vagina to stop sperm from entering the uterus. Using a diaphragm may require some practice and needs to stay in the vagina for at least 6 hours after sex. When used correctly, diaphragms are 94% effective.

Long acting reversible contraception (LARC)

LARCs can protect women for weeks, months or even longer without having to do anything. For those that can forget pills easily, LARCs are a safer choice.

Intrauterine device (IUD) is a small, T-shaped device made of progesterone or copper. It is fitted inside a woman’s uterus and can stay in place for 3-10 years. It is long-acting, reversible and highly effective (up to 99.8%).

The contraceptive implant is a flexible rod that is placed under the skin in a woman’s arm. It releases the hormone progesterone to stop the ovary from releasing eggs and thickens the cervical mucus to discourage sperm entry. The implant is fitted in a small procedure under local anaesthetic, and needs to be replaced after three years. Like an IUD, the contraceptive implant is also highly effective and reversible. However, up to 10% of patients report breakthrough bleeding, weight gain, acne and occasionally, loss of libido.

The contraceptive injection slowly releases a synthetic progestogen hormone over 3 months. This method is mainly for women who cannot tolerate estrogen-containing medications, are smokers, or have a history of thromboembolic disorders. It is very effective but does require you to keep track of the number of months lapsed. Nowadays, contraceptive injection is phasing out with the introduction of newer IUDs and implants.


Sterilisation Is when either the man or the woman undergoes an operation to become sterile. The woman’s procedure involves blocking the fallopian tubes in what’s known as “tubal occlusion and tubal ligation”. The man’s operation is called a vasectomy, which can be more than 99% effective. Usually, sterilisation is for people who have already achieved their desired family size. Although vasectomy reversal is possible, it is not always straightforward to have children after the operation.

Emergency contraception

Emergency contraception is used immediately following unprotected sex, condom breakage, diaphragm dislodging, or other unplanned intercourse. It is important to note that no emergency contraceptive is perfectly effective. Generally, the sooner you take it, the more effective it is. Most women will have a period within 7 days after the expected date. While menstrual irregularity in the cycle following emergency contraception is normal, women should seek a pregnancy test if period is delayed by more than 7 days.

If you still can’t decide which contraception method suits you best, please talk to a healthcare provider. Dr. Alex Polyakov is a Melbourne-based gynaecologist and obstetrician