Birth weight and fetal growth in infants born to female hairdressers and their sisters.

OBJECTIVES: To investigate birth weight and fetal growth in female hairdressers, while controlling for intergenerational effects and effects related to childhood exposures. METHODS: A cohort of women who had attended vocational schools for hairdressers were compared to their sisters with respect to birth weight and fetal growth (measured as small or large for gestational age, SGA and LGA, respectively) in their infants. In total, 6223 infants born to 3137 hairdressers and 8388 infants born to 3952 hairdresser's sisters were studied. RESULTS: Among the infants born to the hairdresser's sisters, the distribution of birth weights were wider than that among the infants born to the hairdressers. This was also reflected in that hairdresser cohort affiliation tended to be protective against both SGA (odds ratio 0.80; 95% confidence interval 0.49-1.31) and LGA (0.77; 0.54-1.09). For LGA, this effect was even more pronounced among women who had actually worked as a hairdresser during at least one pregnancy (0.60; 0.39-0.92). The infants born to these women also had a significantly lower mean birth weight (3387 g vs 3419 g; p=0.033). CONCLUSIONS: The results from the present study suggest that infants born to hairdressers have a decreased risk of being LGA. This is most likely not caused by a shift in birth weight distribution or abnormal glucose metabolism