Women's Health

Menstruation & Hormones: Understanding Your Own Cycle


The menstrual cycle is a series of changes a female body goes through each month in preparation for a possible pregnancy. Understanding one’s own menstrual cycle can be empowering to many women since it helps in family planning, management of any menstrual symptoms, and being alert when there might be a health issue, which may call for an appointment with a qualified gynaecologist in Singapore

Menstrual bleeding happens because the lining of your uterus has prepared itself for a possible pregnancy by becoming thicker and richer in blood vessels. If pregnancy fails to occur, this thick uterus lining is shed accompanied by bleeding.

Common terms used to describe the blood loss that women experience during this time include menstruation, period, and menses.

For most women, menstruation happens in a fairly predictable pattern. A menstrual cycle is marked by the length of time from the first day of menstruation to the first day of the next menstruation. It typically lasts around 28 days, ranging from 24-35 days.

The Menstrual Cycle In 3 Phases 

Follicular Phase (Days 1-14) 

This phase begins on the first day of menstruation and ends on the day of ovulation. While menstrual bleeding takes place at the beginning of this phase, the ovaries are simultaneously preparing to ovulate again.

During this phase, the pituitary gland (located at the base of your brain) produces a follicle stimulating hormone (FSH) that causes 10-20 follicles in your ovary to develop. Follicles are very tiny fluid-filled sacs, each containing an immature egg. 

Usually, a single follicle becomes dominant with a matured egg that is released at ovulation. If more than one egg reaches maturity and gets fertilised, it could lead to twins or more.  

The maturing follicle sets off a surge in estrogen, which causes the lining of your uterus to thicken and become enriched with blood vessels. This creates a nutrient-rich environment for an embryo to grow.

Ovulation Phase (Day 14)

Rising levels of estrogen throughout the follicular phase stimulates the production of gonadotropin-releasing hormone (GnRH) which in turn stimulates the production of luteinizing hormone (LH).

The surge in LH is responsible for triggering ovulation. The mature egg is released and travels down the fallopian tube to be fertilised, leaving behind an empty follicle. If there is no fertilisation, it survives for up to 24 hours before disintegrating. 

The surge in LH also leads to a brief surge in testosterone, which increases sex drive, coinciding with the most fertile time of the cycle.

Luteal Phase (Days 14-28)

Post-ovulation, levels of luteinizing hormone (LH) and follicle stimulating hormone (FSH) drop.

The empty follicle left behind by the egg forms a temporary hormone secreting body called the corpus luteum in the ovary, responsible for production of progesterone and estrogen. 

The corpus luteum plays a vital role in sustaining early stages of pregnancy. If the egg is fertilised, the corpus luteum continues to secrete progesterone which is essential during pregnancy since it supports the growth of your uterus lining and also improves oxygen supply and blood flow.

However, if fertilisation has not occurred, the corpus luteum becomes inactive and breaks down, causing progesterone and estrogen levels to drop and in turn, triggers menstruation. The reproductive cycle thereby repeats. 

Important Menstrual Cycle Hormones & Their Functions

Follicle Stimulating Hormone (FSH)

This hormone is released from the pituitary gland, and its primary function is to stimulate your ovarian follicles to produce a mature egg.


Estrogen is a female sex hormone that is responsible for growing and maturing your uterine lining. This is the lining that is usually shed during menstruation. Estrogen is produced by your ovaries and adrenaline glands. The hormone is abundant during the follicular phase of the menstrual cycle.

Luteinizing Hormone (LH)

LH is also produced by the pituitary gland during ovulation. The hormone triggers ovulation, causing the rupture of a mature ovarian follicle which releases an egg ready for fertilisation.


This is an important sex hormone for both men and women, although women have lower levels. Testosterone is produced by the adrenal glands and ovaries, and its levels increase during ovulation. Testosterone helps you to maintain bone strength, muscle mass and enhances sex drive.


This is another female sex hormone that balances the effects of estrogen. This hormone is produced after the ovulation phase of the menstrual cycle by the corpus luteum.

The primary function of progesterone is to control the buildup of your uterine lining and to help maintain a mature uterine lining during early pregnancy. If there is no pregnancy, your progesterone levels will drop as the corpus luteum becomes inactive, and your uterus lining disintegrates, leading to menstruation.

Common Causes Of Menstrual Cycle Irregularities 

Research shows that menstrual irregularities can have various causes, including hormonal imbalances, pregnancy, and diseases. The following some of the common causes of irregular menstrual cycles.

Pregnancy & Breastfeeding

Missed periods can be an early indication of pregnancy. If you miss or notice changes in your period and you have had sex recently, make sure that you take a pregnancy test to determine if you are pregnant.

If you are breastfeeding, you may also experience a delay in the return of your period after pregnancy. Prolactin – a hormone responsible for milk production- suppresses your reproductive hormones leading to light period or no period at all while breastfeeding.

Eating Disorders, Excessive Exercising Or Extreme Weight Loss

Rapid weight loss, intense exercising, or eating disorders such as anorexia nervosa can also disrupt your menstrual cycle.

Typically, you are considered underweight if your body mass index is lower than 18.5. Failing to consume enough calories can interfere with the production of menstrual hormones such as luteinizing hormones.

Polycystic Ovarian Syndrome (PCOS)

PCOS is a condition in which several small fluid-filled sacs referred to as cysts develop in your ovaries. Women with PCOS may fail to ovulate, leading to irregular periods or none at all.

Women with PCOS also have unusually high levels of testosterone.  Common symptoms of this condition include acne, obesity, and excess hair growth.

Premature Ovarian Failure

Premature ovarian failure is also referred to as ovarian insufficiency. This is a term used to describe the loss of normal ovarian function before you reach the age of 40. Women who have this condition may experience irregular periods for several years.

Pelvic Inflammatory Disease (PID)

Pelvic inflammatory disease refers to an infection of the female reproductive system. If detected early, PID can be treated with antibiotics, but if it spreads, it can damage your fallopian tubes and uterus, causing chronic pain. Common symptoms of PID include bleeding between your periods or after sex.

Uterine Fibroids

Fibroids are noncancerous tumours that develop in the wall of your uterus. They range in size from as small as an apple seed to as large as a grapefruit.

Growth of fibroids can make your periods quite painful and even heavy enough to cause anaemia. Symptoms of fibroids include pain during sexual intercourse, pain in your legs, and pelvic pain. 

When Should You See A Gynaecologist?

 There are a lot of things that you can do to prevent menstrual irregularities. Use of birth control pills and treatment of underlying medical problems such as PCOS and eating disorders have been proven to help.

Make an appointment with your gynaecologist if:

  • Your periods suddenly become irregular
  • You develop severe pain during your period
  • You have not has your period for three months or more, and you are not pregnant
  • Your periods are less than 21 days or more than 35 days apart
  • You need more than one pad or tampon every hour
  • You bleed between your periods

Be Aware Of Changes In Your Body

It is important to stay attuned to your body and menstrual cycle for important reasons. Every woman’s body is different, and what is normal to others might not be the same for you. 

Be alert of any sudden changes in your menstrual cycle, for example when you get your period and how long your cycles last. If you notice anything unusual, make sure to consult an accredited gynaecologist soonest for medical advice. 



About SOG Health Pte. Ltd.

Established in 2011, SOG Health Pte. Ltd. (“SOG”) is a leading healthcare service provider dedicated to delivering holistic health and wellness services to the modern family.

With a long and established track record in Singapore providing Obstetrics and Gynaecology (“O&G”) services such as pre-pregnancy counselling, delivery, pregnancy and post-delivery care, the Group has since further expanded its spectrum of healthcare services to include Paediatrics, Dermatology, and Cancer-related General Surgery (Colorectal, Breast & Thyroid).

The Group’s clinics, under its four operating segments of O&G, Paediatrics, Oncology and Dermatology, are strategically located throughout Singapore to provide easy access to its patients.

  • Obstetrics
  • Gynaecology
  • GynaeOncology
  • Breast, Thyroid & General Surgery
  • Colorectal, Endoscopy & General Surgery
  • Dermatology
  • Paediatrics

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