Since the beginning of the twenty-first century, Vietnam has been facing an imbalance in the sex ratio at birth: at the national level, because of the use of prenatal sex selection, 113 boys are currently being born for every 100 girls. This practice has only emerged recently due to the late advent of high quality ultrasounds, whose use has increased within the private health system, according to a marketbased approach rather than one based on public health. The preference for sons is exploited by health practitioners for commercial purposes: ultrasounds are used as pre- and post-conception methods, in order to fulfill gendered reproductive objectives. It falls within a large spectrum of traditional techniques and practices aimed at conceiving boys, and reproductive strategies to ensure the birth of a son. In fact, the development of ultrasounds acts as a constraint because couples can no longer use the excuse of chance to justify why they do not have a son.