The women completed the data collection form, which was used to collect data about socioeconomic and obstetric characteristics, medical and reproductive histories, and lifestyles. The second data collection form which was completed by trained interviewer was designed to obtain information about the use of cell phones during pregnancy. For the consideration of cell phones effects, we measured the average calling time per day, the location of the cell phones when not in use (in handbags, clothing pockets, or ≥60-70 cm away from the body), use of hands free equipment, use of phones for other applications (to send messages, to listen to music, and to play games), the specific absorption rate (SAR) reported by the manufacturer and the average of the effective SAR (average duration of calling time per day × SAR). SAR indicates how much electromagnetic energy is absorbed by body tissues. This parameter shows the estimation of total EMF energy. The effective SAR can show the exposure of ELF estimation from mobile phones indirectly. We investigated the data about the SAR of each mobile phone model from SAR.ir site.