Your monthly cycle and ovulation: what happens in each phase

Periods are a monthly report card of your hormones. If you can read the card, a lot of PCOD starts to make sense. So let us walk through one ordinary cycle first.

How to count a cycle

Day 1 is the first day of bleeding. The cycle ends on the day before your next period starts. A typical cycle is 21 to 35 days. Bleeding lasts 2 to 7 days, and a pad usually needs changing every 3 to 4 hours or less often.

The textbook cycle is 28 days, but plenty of healthy women run at 24 or 33. The gap matters more than the exact number. Gaps that stay between 21 and 35 days are typical.

The four phases

A cycle is a conversation between three places: the brain, the ovaries and the womb. The brain sends signals called FSH and LH to the ovaries. The ovaries send back estrogen and progesterone.

Period, days 1 to 5

The womb lining, built up over the last month, sheds as bleeding. No pregnancy happened, so the body clears the lining and starts over.

Growing phase, days 1 to 13

This phase overlaps with the period. FSH from the brain grows a few egg sacs in the ovary. They are called follicles. As they grow they make more estrogen, and estrogen rebuilds the womb lining. Typically one follicle wins and keeps growing.

Ovulation, about day 14

Estrogen climbs, and then the brain sends a sharp surge of LH. That surge releases the egg from the winning follicle. The days around ovulation are when pregnancy is most likely.

In a longer cycle ovulation comes later than day 14. A rough rule is that it happens about two weeks before the next period.

Preparing phase, days 15 to 28

The empty follicle starts making progesterone. Progesterone prepares the womb lining for a possible pregnancy and keeps it steady. If there is no pregnancy, progesterone and estrogen fall and the next period starts.

What changes in PCOD

In PCOD many follicles start to grow, but they stall. The egg is often not released on time, or not at all. No ovulation means no progesterone rise.

That one change explains a lot.

• Periods become late or missed, because nothing signals the lining to shed on schedule.
• Periods can turn heavy. Estrogen keeps building the lining, and without progesterone to steady it, the lining gets thick and sheds unevenly.
• Getting pregnant takes longer, because pregnancy needs an egg.

It helps to know this is not all or nothing. Some women with PCOD ovulate now and then and conceive naturally. Others ovulate in most cycles but have other signs, such as acne or extra hair. Also, a period on the calendar does not always mean an egg was released, so regular-looking periods can still sit alongside PCOD. Tests tell.

Track the first day of every period

The simplest tool is a notebook or a note on your phone. Write down:

• the first day of each period
• how many days it lasted
• whether the flow was light, medium or heavy
• pain, scored from 0 to 10
• your weight, and anything unusual

Three months of notes make a doctor's first conversation faster and more accurate. They show the length of your cycles and whether you skip months.

When to see a doctor

Your cycle is worth checking when:

• cycles are longer than 35 days, or you have fewer than 8 periods a year
• you skip months, or you spot between periods
• you have no period for 3 months and you are not pregnant

See a doctor soon if you soak a pad every hour for 2 hours in a row, pass large clots, bleed for more than 7 days or have severe pain.

For teens, irregular periods are common in the first 2 to 3 years after the first period, because the body is still settling in. A doctor can tell whether it is that, or something that needs care. See a doctor if there is no period by age 15, or more than 3 years after breast growth began.

This article is education, not a diagnosis. Whether your cycle is typical for you is a decision for your doctor, using your history, tests and a scan.