The choice of a method of contraception is individual, based on factors including good advice from the general practitioner. There are various reliable forms of contraception available, such as the contraceptive pill, the copper or hormone-containing coil (intrauterine device), the vaginal ring, the contraceptive patch, the contraceptive injection, contraceptive implants, and male sterilization (vasectomy) or female sterilization. When choosing for a combined hormonal preparation the preference is for a pill containing levonorgestrel and ethinylestradiol 30 μg. Women aged ≥ 35 years who smoke and are not prepared to stop are advised against taking combined preparations. Only liver-enzyme inducing drugs have been proven to have relevant interaction with hormonal contraceptives; this has not been proven in the case of antibiotics. A transvaginal ultrasound is not necessary following an uncomplicated insertion of an intrauterine device.