Understanding Out-of-Phase Ovulation (LOOP Cycles) in Perimenopause

Perimenopause is a time of hormonal transition, and for many women, one of the earliest signs of this shift is a sudden change in menstrual cycle patterns. You may notice your cycles becoming unusually short one month and surprisingly long the next. This irregular rhythm isn’t random — it’s often caused by something called out-of-phase ovulation, also referred to as LOOP cycles (Luteal-Out-Of-Phase cycles).

In this blog, we’ll break down what LOOP cycles are, why they happen, and what they mean for your perimenopause journey.

What Are LOOP Cycles?

A LOOP cycle is a menstrual pattern that develops during perimenopause when ovulation occurs earlier than it should — sometimes during the late luteal phase or even immediately after a period ends.

In a typical cycle, ovulation happens mid-cycle. But in a LOOP cycle, the next dominant follicle begins growing far too early, disrupting the normal hormonal rhythm.

This “out-of-phase” ovulation leads to cycles that swing between very short and very long, creating a distinctive pattern that many women experience in early perimenopause.

Why Does Out-of-Phase Ovulation Happen?

The main driver behind LOOP cycles is high early-cycle FSH (follicle stimulating hormone). As the ovaries become less responsive during perimenopause, the body compensates by producing more FSH in an attempt to stimulate follicle growth.

This elevated FSH can trigger a follicle to develop too early, before the previous cycle has fully ended. This breakdown in the usual hormonal feedback loop is a hallmark of perimenopause.

Hormone “Stacking” and Why It Matters

When a follicle begins growing early, it produces estradiol on top of the estradiol already present from the prior cycle. This creates what clinicians often call “estrogen stacking.”

The result?

Estradiol levels can become very high, which contributes to:

• irregular cycle lengths

• unexpected symptoms

• cycle variability (short → long → short → long)

  
  

This hormonal overlap is a major reason why perimenopause can feel unpredictable.

How LOOP Cycles Affect Your Menstrual Cycle

A LOOP event can cause two very different outcomes:

1. If the early follicle ovulates:

The cycle becomes short because ovulation occurred prematurely.

2. If the early follicle does not ovulate (anovulatory cycle):

The cycle becomes long, as the body delays menstruation without a clear ovulation event.

This creates a recognizable pattern of:

Short cycle → Long cycle → Short cycle → Long cycle

This alternating pattern is one of the classic signs of early perimenopause.

Are LOOP Cycles Normal?

Yes — LOOP cycles are common and normal during the perimenopause transition.They do not mean something is wrong; in fact, they are often one of the earliest indicators that perimenopause has begun.

As ovulation becomes less predictable and hormones fluctuate, the menstrual cycle reflects these internal changes.

What You Might Notice

Women experiencing LOOP cycles commonly report:

• cycles shorter than 21 days

• cycles longer than 35 days

• cycles alternating between short and long

• changes in menstrual flow

• changes in PMS symptoms

• fluctuating estrogen-related symptoms (breast tenderness, mood shifts, spotting)

  
  

Understanding the pattern can help you recognize where you are in the perimenopause transition.

How to Support Your Cycle During Perimenopause

While LOOP cycles are normal, tracking your cycle can help you understand your symptoms and guide supportive care. You may consider:

• tracking cycle length and ovulation patterns

• noting symptoms that coincide with short vs. long cycles

• discussing hormonal changes with a healthcare provider

• exploring nutritional, hormonal, or lifestyle support if symptoms become disruptive

  
  

Awareness is key — perimenopause doesn’t have to feel confusing once you understand what’s happening biologically.

The Bottom Line

LOOP cycles occur when ovulation happens out of sync due to rising early-cycle FSH levels. This leads to alternating short and long menstrual cycles and is one of the early signs of perimenopause.

Your cycle isn’t malfunctioning — it’s responding to the hormonal shifts that naturally occur as fertility declines. Understanding LOOP cycles can help you navigate perimenopause with confidence and clarity.