Cervical incompetence is when the cervix measures less than
**Core Concept**
Cervical incompetence is a condition where the cervix fails to maintain a pregnancy due to premature dilation or effacement. This can be caused by various factors, including cervical trauma, uterine anomalies, or genetic predisposition. The diagnosis is often made based on the cervical length measured by transvaginal ultrasound.
**Why the Correct Answer is Right**
The American College of Obstetricians and Gynecologists (ACOG) defines cervical incompetence as a cervix that measures less than 25 mm in length at 24 weeks of gestation. This measurement is crucial because a shorter cervix is more likely to dilate prematurely, leading to preterm birth. The cervix is composed of two layers: the ectocervix and the endocervix. The ectocervix is the external portion, while the endocervix is the internal mucous membrane. The cervix is also divided into the isthmus, which connects the cervix to the uterus, and the cervical canal.
**Why Each Wrong Option is Incorrect**
* **Option A:** This option is incorrect because the American College of Obstetricians and Gynecologists (ACOG) does not recommend measuring the cervix at less than 20 mm for the diagnosis of cervical incompetence.
* **Option B:** This option is incorrect because the cervix can be normal in length but still be incompetent. A shorter cervix is not the sole determining factor for cervical incompetence.
* **Option D:** This option is incorrect because the cervix can be longer than 30 mm and still be incompetent. Cervical incompetence is a complex condition that cannot be diagnosed solely based on the cervix length.
**Clinical Pearl / High-Yield Fact**
It's essential to note that cervical incompetence can be asymptomatic until the onset of preterm labor or cervical dilation. Therefore, regular ultrasound assessments are crucial in monitoring cervical length and preventing preterm birth.
**Correct Answer: C. 30 mm**