A focused ultrasound that measures the cervix to identify pregnancies at risk of preterm birth, while also evaluating placental position and screening for vasa previa.
A transvaginal ultrasound uses a slender probe placed in the vaginal canal, so the cervix can be measured directly without the abdominal wall, bladder, or surrounding tissue blurring the image.
The cervix is the lower part of the uterus. In a healthy pregnancy it stays long, thick, and closed until your baby is ready to be born. If it begins to shorten, thin, or open too early, the risk of spontaneous preterm birth goes up.
We typically look for a cervical length greater than 25 millimeters between 18 and 24 weeks. We also watch for funneling, when the inner part of the cervix begins to open into a V or U shape even while the outer part stays closed.
Cervical shortening can occur even in patients with no prior risk factors or warning symptoms. Because of this, many experts support evaluating cervical length during the mid-trimester anatomy ultrasound (18–24 weeks) as part of routine pregnancy care.
Measuring cervical length is simple, safe, and helps identify pregnancies that may benefit from early treatment to reduce the risk of preterm birth. Early detection allows us to act early — often before symptoms appear.
The placenta delivers oxygen and nutrients to your baby. Where it sits inside the uterus matters for how you will deliver. Placenta previa is when the placenta covers all or part of the cervical opening, which can cause heavy bleeding during a vaginal delivery.
Transvaginal imaging gives a clear, unobstructed view of the relationship between the placental edge and the cervix, so the diagnosis is accurate. An abdominal scan can sometimes give a false positive when the bladder is full or the lower uterus is contracting.
Vasa previa is a rare but very serious condition where unprotected fetal blood vessels run across the cervical opening. If those vessels rupture during labor or when the water breaks, it can cause rapid, life-threatening blood loss for the baby.
During your exam we use Color Doppler imaging, which shows blood flow in real time, to sweep the area over the cervix and confirm that no fetal vessels are crossing it. When we do find vasa previa, we build a specialized care plan with your OB, usually a scheduled cesarean before labor begins.
We know a transvaginal ultrasound can feel more personal than an abdominal scan. Here is exactly what happens, step by step, so you arrive knowing what to expect.
Don't see your question? Call our office and we will be happy to walk you through anything before your appointment.
Most patients arrive with a referral from their OB. If you don't have one yet, we can help coordinate. Same-week appointments are usually available.