The Relationship Between Endometrial Thickness and Menstruation

For most women, menstruation typically begins when the endometrial lining reaches a thickness of around 1 cm. However, this can vary significantly from person to person. Some women may experience their period with an endometrial thickness as low as 5–6 mm, while others may not menstruate even when their lining measures up to 1.5 cm. Therefore, the exact thickness that triggers menstruation can differ, and other factors such as hormonal balance and follicular development play a crucial role.

Understanding Follicular Development and Menstruation

In addition to endometrial thickness, the condition of the ovarian follicles is an important factor in predicting menstruation. Generally, ovulation occurs when a dominant follicle reaches a size of approximately 1.8–2 cm. Following ovulation, menstruation usually begins about two weeks later. However, if no large follicles are observed during an ultrasound and only smaller follicles measuring 7–8 mm are present, it may be unclear whether ovulation has occurred. In such cases, doctors often rely on endometrial thickness to make an educated guess.

Using Endometrial Thickness to Predict Your Period

If the endometrium measures over 8 mm, it's possible that menstruation may begin within the next two weeks. Women with a thicker lining—around 1.3 to 1.5 cm—may expect their period to start within the next seven days. It's important to note that these predictions are not always accurate and can vary depending on individual physiology.

Hormonal Influence on the Menstrual Cycle

The menstrual cycle is also heavily influenced by sex hormone levels, particularly estrogen and progesterone. Even if these hormones are within a normal range, previous uterine damage or scarring can prevent the endometrium from thickening properly. In such cases, some women may menstruate when their endometrial lining is only 5–6 mm thick. While a thickness of around 1 cm is common before menstruation, it's not a universal rule and should be interpreted alongside other clinical findings.