The standard tests performed in a prenatal visit do not make a woman niddah.
You should still observe your veset haflagah as scheduled, regardless of the timing of your visit. However, you may rely on the opinions that only one bedikah need be performed on the onat veset and time that bedikah with an eye to your appointment. For example, if the appointment is the day before your onah, you may perform your bedikah at the very end of your onah to minimize the chance of finding blood on the bedikah. If your appointment is the day of your onah, you would perform the bedikah right before the appointment.
As always, you may wear a colored undergarment on your veset day.
Do be in touch if there is any further question.
We have some appropriate books listed on our website. You may also be interested in our Marriage Companion course, which includes units on pregnancy, childbirth, postpartum, and breastfeeding. The best gift you can give your child is a mother who loves God, her husband, and herself. Working on developing and enhancing those three relationships is a lifetime project, but a lot can be accomplished over nine months. BeSha’ah tovah!