Ovulation | Medical Science Optional Notes for UPSC PDF Download

Introduction

Ovulation takes place 10-12 hours after the peak of luteinizing hormone (LH) and approximately 36 hours after the LH surge. The follicular phase, also known as the proliferative phase, is the period in the menstrual cycle when ovarian follicles mature. It spans from the onset of menstruation to the initiation of ovulation.

During the follicular phase, estrogen levels reach their peak towards the phase's conclusion. This surge in estrogen triggers an increase in luteinizing hormone (LH) and follicle-stimulating hormone (FSH) levels. This surge persists for 24 to 36 hours, resulting in the rupture of ovarian follicles and the release of the oocyte from the ovary through the oviduct.

The primary physiological indicator signaling impending ovulation is the LH surge. An LH peak level of 75 ng/mL is essential for ovulation, and this surge takes place 24-36 hours before the actual ovulation. The LH peak persists for a duration of 24 hours.

The LH surge leads to the following outcomes:

• Completion of the meiosis of the ovum
• Ovulation
• Formation and development of the corpus luteum

Tests for Ovulation

Understanding the timing of ovulation within the menstrual cycle holds significance for both enhancing fertility and family planning.

Basal Body Temperature (BBT) Method:
It is established that basal body temperature falls around the time of ovulation, typically by about 1/2° F. A convenient and reasonably reliable indicator of ovulation time is a change—usually a rise—in basal body temperature. This increase begins 1-2 days after ovulation. For accurate temperature charting, women interested in tracking their ovulation should use a digital thermometer and measure their temperatures (orally or rectally) in the morning before getting out of bed. The likely cause of the temperature change during ovulation is the increase in progesterone secretion, given that progesterone has thermogenic properties.

Fern Test:
This test illustrates the cyclic alterations in cervical mucus influenced by various hormones. In the preovulatory phase (estrogenic phase), a drop of cervical mucus spread and dried on a glass slide exhibits a palm leaf or fern-type reaction, attributed to the presence of sodium chloride. This reaction diminishes post-ovulation under the influence of progesterone. Progesterone causes the cervical mucus to thicken, become tenacious, and impervious to sperm and bacteria.

Spinnbarkeit Phenomenon or Thread Test:
Ovulation mucus displays remarkable elasticity, withstanding stretching up to 10 cm. This quality is termed spinnbarkeit or the thread test for estrogen activity. During the secretory phase, cervical mucus becomes tenacious, and its viscosity increases, causing it to lose the spinnbarkeit property and fracture under tension. This characteristic is referred to as tack.

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Endometrial Biopsy:
Evidence of secretory changes confirms that the menstrual cycle has been ovulatory.

Daily Ultrasound:
Ultrasonic visualization of the ovaries is conducted from the 10th to the 16th day of the menstrual cycle. This noninvasive, accurate, and safe method observes the follicle's daily growth rate of 1-2 mm, reaching 20 mm or more at midcycle when follicular rupture and ovulation occur. The abrupt disappearance of the follicle, the presence of free fluid in the pouch of Douglas, and the growth of the corpus luteum are observable outcomes.

Hormonal Studies:

• Plasma Progesterone: Levels rise following ovulation.
• LH Surge.
• FSH: Elevated FSH levels are evident in cases of ovarian failure.

Reproductive physiology-Repeats

Ovulation -Repeats 

• Define ovulation and identify the hormones essential for the process. Explain the significance of knowing the timing of ovulation. (2014)
• Discuss tests that indicate the occurrence of ovulation in females. (2011)