Why does vaginal bleeding occur in pregnancy?

Several reasons. The blood can come from the cervix which can bleed easily. It can also come from the placenta with implantation or with miscarriage.
Vaginal Bleeding. Vaginal bleeding during pregnancy is a serious condition. It may be due to placenta previa. Sometimes it heralds the beginning of labor, if associated with mucus. Consult your OB immediately, if bleeding.

Related Questions

Had abnormal vaginal bleeding and was told it was fibroids, period has not yet come, what should I do? Took pregancy tests, negtv female 24 black

Several options. One might be to try a Progesterone withdrawal to go ahead and have a period. Important to understand your reporductive goals going forward in concert with how disruptive your abnormal periods are. This is a convo to have with your obgyn. If not interested in pregnancy birth control pills can make your bleeding less and more regular for example. Read more...
Common . It is common to have irregular heavy periods. It is more common when you have fibroids. Missing your cycle is also common. Irregular periods are most common when the fibroids invade the uterine cavity called the endometrium. The symptoms of abnormal bleeding are often caused by other problems as well including polyps, hormonal changes, infections (chlamydia) and cancer of the cervix or uterus. Read more...