My Placenta Is Low-Lying. Now What?

Now that most pregnant women have a midpregnancy ultrasound, they are often alerted to findings of uncertain significance. One of the most common of these involves the placenta. A placenta is low-lying when the lower edge extends to within 2 centimeters of the internal cervical opening or os. This is different from a placenta previa which actually covers the internal os. A group of investigators at the Brigham and Women's Hospital in Boston reported on their experience with the eventual outcome of pregnancies complicated by these low placentas.

Here's the short answer: Most of these situations resolve by the end of the pregnancy.

In total, 1220 of 1240 low-lying placentas (98.4%) that had sonographic follow up resolved to no previa before delivery; 89.9% of placentas cleared the cervix by 32 weeks, and 95.9% cleared by 36 weeks.

A small minority were not so lucky.

Twenty patients (1.6%) had persistent sonographic placenta previa or a low-lying placenta at or near term, including 5 complete previas, 7 marginal previas, 5 low-lying placentas, and 3 vasa previas; all had cesarean deliveries.

So, about 98/100 times all turns out well. In about 2/100 cases, the situation persists. Moreover, a very few unfortunate women were found to have vasa previa, a condition in which fetal blood vessels actually cross that internal os in front of the baby. Think about that for a moment. If the baby descends toward the birth canal and puts pressure on these blood vessels, those vessels can tear, resulting in a fetal hemorrhage, often severe.

So what should be the plan if they do find a low-lying placenta during your ultrasound? The authors suggest a repeat sonogram after 28-30 weeks to confirm resolution, repeating again at 34-36 weeks if the situation remains the same. During those studies, a search for vasa previa can also be conducted.

So if you're told you have a low-lying placenta, you should be optimistic but should follow up. The late Ronald Reagan said it best: "Trust but verify."

For more information or to schedule an ultrasound, please call: (718) 925-6277.