Fetal sex can be detected by USG at
**Question:** Fetal sex can be detected by USG at
A. 11-14 weeks
B. 18-22 weeks
C. 24-28 weeks
D. 34-36 weeks
**Core Concept:** Transvaginal ultrasound (TVUS) and transabdominal ultrasound (TAS) are commonly used methods for determining fetal sex during pregnancy.
**Why the Correct Answer is Right:** Fetal sex can be determined using ultrasound techniques due to the presence of the Y chromosome-specific genes, which produce specific proteins. In males, these proteins form the SRY gene and in females, they produce no such proteins. The testes in males begin to descend into the scrotum around 11-14 weeks of gestation. By around 18-22 weeks, the fetal genitals are well-developed and can be accurately assessed. This is when the correct fetal sex can be determined with a high degree of accuracy.
**Why Each Wrong Option is Incorrect:**
A. 34-36 weeks: This option is incorrect because fetal genital development is more advanced at a younger gestational age, allowing for more accurate determination of fetal sex.
B. 24-28 weeks: Although fetal genital development is more advanced, this option is still too late compared to the correct gestational age range.
C. Transvaginal ultrasound (TVUS) and transabdominal ultrasound (TAS) are both methods used to determine fetal sex, but the correct answer lies in the gestational age at which fetal genital development is well-established.
**Clinical Pearl:** Determining fetal sex using ultrasound is a routine part of prenatal care and can help in genetic counselling and family planning decisions. It is essential to accurately assess fetal genitalia at the appropriate gestational age to avoid misinterpretation or false results.
**Correct Answer:** B. 18-22 weeks
**Explanation:** At around 18-22 weeks, fetal genital development is well-established, and the genitals can be accurately assessed for determining fetal sex. This is due to the presence of the Y chromosome-specific genes which produce proteins that are not found in females. This allows for a higher degree of accuracy in determining fetal sex during this gestational age range.