A thread of mucus formed in the cervix which is used in determining the time of ovulation. At this time it can be drawn out on a glass slide to its maximum length.
Evaluation of the elasticity of cervical mucus used to determine time of ovulation. The cervical secretion is aspirated and placed on a slide. SBK is measured by pulling upward on the secretion with a forceps. Before ovulation, there is no elasticity. On the day of ovulation, elasticity is good, measuring 12 to 24 cm or more. The day after ovulation, elasticity diminishes. Not all women have clear-cut SBK changes. Therefore, this test is used in conjunction with other signs of ovulation.