Masturbation is not recommended no matter how many weeks pregnant you are. At 13 weeks of pregnancy, masturbation is also not allowed. During pregnancy, it is more prudent to be sexually active. You should not have intercourse during the first 3 months of pregnancy, and also during the late 3 months of pregnancy. During the 4th-6th months of pregnancy, you can have sex moderately, but if the pregnant woman has special circumstances, you should not have intercourse during the entire pregnancy. Masturbation is also a sexual act, and a less healthy one. If a pregnant woman masturbates during pregnancy, it is likely to increase the probability of vaginal inflammation, in addition to the risk of miscarriage due to uterine contractions after the stimulation of sexual intercourse.