How can hormones influence sexual development during embryonic growth?

In human embryology, sexual development is a process where neutral embryonic structures differentiate into male or female organs based on genetic and hormonal influences. While genetic sex is determined at fertilization, all embryos possess the potential to develop either male or female genitalia and will naturally follow a feminizing path unless specific masculinizing influences occur during gestation.1

Hormones play a critical role in this differentiation:

• Masculinization: In XY fetuses, the testes secrete testosterone, which stimulates the Wolffian ducts to develop into the male genital tract (including the ductus deferens and seminal vesicles). Additionally, the testes secrete Müllerian inhibiting hormone, which causes the Müllerian ducts—the precursors to female reproductive organs—to atrophy.12
• Feminization: In the absence of sufficient testosterone or masculinizing signals, the genitalia develop in the female direction, with the Müllerian ducts persisting to form the uterus and fallopian tubes, while the Wolffian system deteriorates.12

External hormonal exposure, such as maternal hormones crossing the placenta, can occasionally override these processes, potentially leading to atypical sexual development.3