Background:
Prenatal secondhand tobacco smoke (SHS) is a significant problem in Hungary's four underdeveloped northeastern counties with a considerable ethnic Roma population. There are 33.2% of non-smoker pregnant women exposed to SHS.

Methods:
Data were collected among mothers delivered with live-born babies 2009-2011 (N=16,859). The neonates' biometric parameters (birth weight, body length, head and chest circumferences) were obtained from hospital records. The response rate was 74.5%. We conducted binary logistic regression analysis of maternal variables for SHS exposure, frequency analysis for central tendencies and dispersion and t-probes for comparing the means of neonatal measurements using significance level p < 0.05 (IBM-SPSS v. 23 software).

Results:
In the non-smoking sample (n = 8,497), pregnant women exposed to SHS were typically less educated (OR = 3.32, 95% CI = 2.64-4.18), of Roma ethnicity (OR = 1.71, 95% CI = 1.36-2.15), living without amenities (OR = 1.70, 95% CI = 1.37-2.11) and of extramarital status (OR = 1.52, 95% CI = 1.27-1.82). The negative difference of birth weight following fetal SHS exposure was 154.9 grams (95% CI = -188.5 - -121.3), the difference of body length - 0.8 cm (95% CI = -1.06-0.6), and of head and chest circumference - 0.5 cm (95% CI = -0.6-0.3 and -0.7-03, respectively). Gestational age was shortened by mean 0.4 week.

Conclusions:
At-home SHS exposure has a serious impact on biometric and obstetrical parameters of newborn babies. The reduction of SHS exposure, especially targeting the most vulnerable pregnant populations should be one of the primary aims of smoking cessation public health programs.