pre-ultrasound period. Standard errors are clustered by state; we have 25 states in our sample.<sup>28</sup> As discussed, we do not observe large differences in the socioeconomic characteristics of firstbornboy and firstborn-girl families (Table 2), so selection on firstborn sex is of limited concern. We nevertheless condition upon SES (education, wealth, caste, rurality); and we effectively difference between firstborn-girl and firstborn-boy families. In an extension, we also allow interactions of all covariates with child gender. To ensure that there remain no unobservables that are potentially correlated with firstborn sex and that influenced girl-outcomes differently from boy-outcomes in the post- relative to the pre-ultrasound era, we introduce mother fixed-effects in a variant of specification (1). While recognizing that the self-reported fertility preference variables are potentially endogenous (being asked during or after the fertility process), we also consider sensitivity of the estimates to conditioning upon mother’s stated desired fertility and desired sex composition of children. Although we show results with and without these endogenous controls, our main specification excludes them. We also show the robustness of our estimates to the inclusion of Female x State x Year FE.

# **4.2.2 Fertility**

We examine the impact of prenatal sex-detection technology on gender gaps in fertility in two ways. First, we test if ultrasound altered the male-bias in the hazard of birth in a given year for firstborngirl versus firstborn-boy mothers.<sup>29</sup> For this specification, we utilize a retrospective mother-year panel in which a woman enters the panel in her year of marriage and exits in the year of survey.<sup>30</sup> For mother _i_ from state _s_ of age _a_ in year _t_ , who has given birth to _b −_ 1 children by _t_ and whose last birth took place _r_ years ago, we estimate the following OLS regression: The outcome variable, _Birthit_ , equals one if the mother gives birth in year _t_ and is zero otherwise. _Post_<sup>1</sup> _t_<sup>,</sup><sup>_Post_2</sup> _t_<sup>,and</sup><sup>_FirstbornGirlj_aredefinedasearlier.Thevector</sup><sup>**Xi**comprisesindicators</sup> for household wealth quintiles, educational attainment of the mother and her husband, caste, religion, residence in a rural area, and mother’s year of birth. We include fixed effects for year ( _ωt_ ), state ( _δs_ ), mother’s age ( _φa_ ), parity ( _ψb_ ), and years since last birth ( _σr_ ), state-specific firstborn-girl fixed effects ( _νsFirstbornGirlj_ ), and state-specific year fixed effects ( _θst_ ).<sup>31</sup> Additionally, we estimate the effects of ultrasound availability on the “stock” of children a

> 28Our results do not change if we instead use robust standard errors without clustering.

> 29Since our empirical strategy relies on the sex of the first birth, the sample excludes the 11 percent of women in the data who had never given birth by the time of the survey.

> 30Out of wedlock birth in India is rare (0.06 percent in 2005 National Family Health Survey).

> 31We also modify this specification by including mother fixed effects to test if ultrasound availability delays time to the next birth for a given mother, conditional upon the time since last birth, in the post-ultrasound (relative to the pre-ultrasound) period and whether this delay is on average greater in firstborn-girl (relative to firstborn-boy) families. The results from this specification are available upon request.

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