For women who are pregnant with a child, a maternity test is often required at 16 weeks of pregnancy. This is when an ultrasound is needed to see the size of the fetus’ biparietal diameter and also the position of the placenta, and then fasting blood is drawn for Down’s syndrome screening. If the ultrasound indicates that the lower edge of the placenta reaches the endocervix, it means that the placenta is in a low position, and it is often likely that vaginal bleeding will occur after strenuous exercise or exertion, which is a sign of abnormal placental position. However, most women will gradually grow into a normal position as their pregnancy weeks increase, so they only need to rest in bed and forbid all strenuous exercise during this period.