**Core Concept:** Cusco's speculum is a medical instrument used for examination of the female reproductive system, particularly during pregnancy. It is named after the Spanish physician Domingo Francisco José de San José y Cusco, who invented it in the late 18th century.

**Why the Correct Answer is Right:** Cusco's speculum is designed to provide support to the gravid uterus by compressing the uterus against the pubic symphysis, facilitating a clear view of the vagina and cervix. It consists of two semi-circular arms made of a semirigid material like steel or plastic, attached to a central axis. When the arms are closed, they are placed over the pubic symphysis and the uterus, while the central axis is inserted into the vagina. This design provides better stability and support to the uterus during examination, improving visualization of the lower genital tract and maternal pelvic organs.

**Why Each Wrong Option is Incorrect:**

A. False (option A) - The correct answer shows the function and design of Cusco's speculum, while option A is incorrect as it discusses another type of speculum (Haller's speculum).

B. False (option B) - Although Cusco's speculum is used for obstetrical examination, this option incorrectly refers to a type of speculum used primarily for gynaecological examination (Muller's speculum).

C. False (option C) - Cusco's speculum is designed for obstetrical examination, not for rectal examination, which is the purpose of the rectosigmoid speculum.

D. False (option D) - Cusco's speculum is specifically designed for obstetrical examination, while the rectosigmoid speculum is used for rectal and sigmoid colon examination.

**Clinical Pearl:** Cusco's speculum is a crucial tool for obstetricians and gynaecologists in performing a thorough examination of the lower genital tract and maternal pelvic organs during pregnancy, childbirth, or postpartum care.