What major developments occur in the fetus during the third month of gestation?

During the third month of gestation, one of the significant developments in the fetus is the differentiation of the external genitalia, which makes it possible to distinguish between male and female gender characteristics through imaging techniques, such as ultrasound. This process occurs as the sex organs begin to develop in response to genetic and hormonal signals, marking the transition from an undifferentiated state to one that reflects the genetic sex of the fetus.

At this stage in gestation, the overall fetal development also encompasses several other important milestones, such as limb growth and increased muscle development, but these do not pertain to gender determination. The visibility of gender via imaging is particularly noteworthy because it provides parents and medical professionals with more detailed information about the fetus's development at around 10 to 12 weeks, setting it apart from the earlier weeks when such distinctions are not apparent.