Another form of passive postnatal sex selection is differential fertility stopping behavior (DSB). DSB is where couples with son preference continue having children until the desired sex composition is achieved. It is more prevalent in contexts where more than two children per woman is the norm (so couples can afford an additional birth to reach the desired number of sons), and prenatal selection methods are not accessible. With this practice, families that have only girls are more likely to continue childbearing. This can result in girls, on average, being disadvantaged as they would have more siblings to compete with for parental resources (Filmer et al. 2008). Empirical evidence from Rosenblum (2013) and Altindag (2016) suggests that families that practice DSB allocate more resources to sons than daughters once the son is born.

_Prenatal sex selection_ Medical diagnostic technology, aimed at detecting fetal abnormalities, has inadvertently been used by parents in societies with entrenched son preference for pre-natal sex selection. If available and accessible, prenatal sex selection is a convenient alternative to postnatal sex selection. Prenatal sex identification technology is easy to use (for doctors) and non-invasive (for the mother), especially as it is bundled with modern antenatal health care services. Coupled with abortion methods, prenatal sex identification technology ensures that the desired sex composition of children is met as unwanted female pregnancies can be terminated within the first two trimesters. These methods also provide couples the luxury of making sex selection decisions privately.

Technology to identify the sex of the fetus has evolved rapidly over the last three decades. The initial methods for sex determination – amniocentesis and chorionic villus sampling – required trained medical personnel and involved some degree of risk to the fetus. Since then, however, sex determination technology has become more accurate, accessible, affordable, and less medically invasive. The ultrasound, which became prevalent in developing countries around the 1980s, allowed accurate identification of the sex of the fetus at 12-16 weeks of pregnancy, and was less invasive than previous sex determination methods (Gilles & Feldman-Jacobs 2012; Bongaarts 2013).

The initial users of ultrasonography for fetal sex determination were from the upper and middle class. The rapid diffusion of this technology across socioeconomic groups, and to rural areas, was aided by several factors. Since the technology was less demanding and risky than previous detection methods, it could be used by non-medical personnel in small health units at a relatively low cost. The declining cost of manufacturing the equipment, and the increasing portability of the equipment further reduced the cost of providing ultrasonography services. Entrepreneurial doctors and health care personnel also played important roles in the diffusion of this technology. With the growing density of private clinics across space, these doctors came to recognize opportunities to tap into the latent demand for prenatal sex determination (Guilmoto 2012a).

In recent years, even more effective methods to determine the sex of the fetus have emerged. One of the main drawbacks of using ultrasonography to determine fetal sex is that it requires the mother to wait until the second trimester. However, blood tests that analyze fetal DNA in the mother’s blood as early as the seventh week of pregnancy have lately been available. These tests have been found to be 98% reliable and are minimally invasive in that they only require a drop of blood from 9