Know your fertile days!

To increase the chances of pregnancy, it is important to know when conception can occur and when the fertile days are. Determining the fertile days is therefore a crucial factor in family planning and reproductive medicine. Understanding the female menstrual cycle and the physiological changes that occur during ovulation is essential.

Overview of the Menstrual Cycle

The menstrual cycle is a complex, hormonally regulated process that averages 28 days, with variations of 21 to 35 days considered normal. It can be divided into the following two main phases:

Follicular Phase
This phase begins on the first day of menstruation and lasts until ovulation. During this phase, the egg cells (oocytes) mature in the follicles of the ovaries. The follicular phase is initiated by an increase in follicle-stimulating hormone (FSH), which stimulates follicle maturation.

Luteal Phase
This phase begins after ovulation and lasts until the onset of the next menstruation. Here, luteinizing hormone (LH) is crucial, triggering ovulation and the transformation of the follicle into the corpus luteum. The corpus luteum produces progesterone, which prepares the uterine lining for a possible implantation.

Highest Chances Around Ovulation

The fertile days occur in the period around ovulation, which is triggered by a sharp rise in LH levels. The so-called LH surge typically occurs 24 to 36 hours before the release of a mature egg into the fallopian tube, which we refer to as "ovulation."

The day of ovulation and the approximately five days leading up to it are considered "fertile days." However, the egg remains fertilizable only for 12 to 24 hours after release.

In addition to LH, estradiol, a form of estrogen, plays a central role. Prior to ovulation, the estradiol level rises. It helps to increase the thickness of the uterine lining and creates a sperm-friendly environment. A high level of estrogen triggers a strong increase in luteinizing hormone.

These hormonal markers are crucial for calculating the fertile phase, as they correlate closely with the likelihood of fertilization. These hormonal changes can be captured through various methods to determine fertile days.

Methods to Determine Fertile Days

There are various methods for determining your fertile days.

LH-based Ovulation Tests
Ovulation tests determine the rise of LH (luteinizing hormone) in urine, providing an indication of ovulation. These tests use immunological reactions to detect the LH peak and can indicate ovulation 24 to 36 hours in advance.

Ovulation Calculators
Based on your usual cycle length, an approximate timing of ovulation is calculated using an algorithm. Since the cycle can vary, this method is not 100% reliable.

The Femsense Cycle Tracker uses precise temperature tracking with a sensor patch to accurately determine ovulation and fertile days by continuously monitoring basal temperature and analyzing the cycle individually.

Cervical Mucus Observation
Cervical mucus changes throughout the cycle due to hormonal influences. During fertile days, cervical mucus (also known as "discharge") becomes clear, fluid, and "stretchy," resembling raw egg whites. This indicates an increased level of estradiol. These changes can be an indicator of fertile days, as sperm-friendly cervical mucus increases the survival time and mobility of sperm.

Basal Temperature Method
Shortly before ovulation, basal body temperature drops by at least 0.2°C and rises again by about 0.2°C to 0.5°C after ovulation (due to progesterone). By measuring daily over months, you can get a good picture of your fertile days. However, measurement errors can occur, so this method is not 100% reliable.

Ultrasound Monitoring
In the context of reproductive medicine, monitoring follicle development through ultrasound allows for a precise prediction of ovulation.

Fertile Days and the Viability of Sperm and Eggs

The fertile days cover a period of about six days—the five days before ovulation and the day of ovulation itself. Sperm can survive in the female reproductive tract for up to five days, while the egg remains fertilizable for only about 12 to 24 hours after ovulation. This narrow timeframe makes accurately determining the fertile days particularly important.

Cycle Variations and Their Impact

For women with irregular menstrual cycles, predicting ovulation is more challenging, as the duration of the follicular phase can vary significantly. Studies show that stress, weight changes, illness, or hormonal imbalances can affect cycle length and thus fertile days:

• Stress and Cycle Variations: A study by Fenster et al. (1999) shows that psychological stress can disrupt the follicular phase and lead to cycle changes.
• Underweight and Overweight: Studies indicate that both underweight and overweight can influence cycle length, as body fat plays a significant role in hormonal balance (Vashishta et al., 2022; Aladashvili-Chikvaidze et al., 2015).
• Hormonal Imbalances: Polycystic ovary syndrome (PCOS) is a common hormonal disorder that causes irregular cycles. Hormonal imbalances significantly affect cycle length and complicate ovulation prediction.

In such cases, combining several methods—such as cervical mucus observation and ovulation tests—can increase accuracy.

Conclusion

Determining fertile days is based on a deep understanding of the hormonal mechanisms and physiological processes that govern the menstrual cycle. Methods such as LH-based ovulation tests, basal temperature measurement, and cervical mucus observation allow for precise narrowing of the fertile window. For women with irregular cycles, it is especially advisable to combine several of these methods to achieve greater accuracy.

FAQ

Can you get pregnant with irregular cycles?
If you have irregular cycles and your period is unpredictable, ovulation can still occur. Even if you do not notice bleeding, an egg can be released and fertilized.

Cycles can also become irregular or absent during the perimenopause phase, but ovulation may still occur, making pregnancy possible.

Can I predict my fertile days with irregular cycles?
Predicting fertile days is more challenging with irregular cycles since the duration of the follicular phase can vary. However, methods such as cervical mucus observation and ovulation tests can provide a way to determine ovulation.

What affects cycle length and ovulation?
Cycle length and ovulation can be influenced by various factors, including stress, weight changes, hormonal imbalances, or health issues. These factors can delay ovulation or cause irregular cycles.

What are the signs of ovulation?
Ovulation presents various physical signs that can help you recognize your fertile period. However, these signs can differ from person to person and may occur individually or in combination. Common symptoms include:

• Change in Cervical Mucus: The mucus becomes clear, stretchy, and resembles raw egg whites, creating a sperm-friendly environment.
• Mittelschmerz: Some women experience mild cramping or pain in the lower abdomen on the side of the ovary releasing the egg.
• Rise in Basal Temperature: Body temperature typically rises by about 0.2°C to 0.5°C shortly after ovulation.
• Increased Libido: Many women experience heightened sexual desire around ovulation.

References