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This is a transcription of a portion of a Healthful Woman podcast.

Beth’s Question

Our first question today is from Beth, whose twins were born at 34 weeks and 1 day after her care team identified elevated Doppler flow in both babies, along with intermittent absent flow in Twin B at her 32-week appointment. Both children are now thriving one-year-olds. Beth’s question centers on the gap between appointments: with Dopplers twice a week and non-stress tests three times a week during that stretch, how could anyone be sure nothing would go wrong over a weekend, when no one was actively watching? She wanted to understand how Dopplers work and how her doctors decided how long it was safe to wait between visits.

Dr. Fox’s Response

Beth, this is a great question, and it deserves some background first. Doppler ultrasound is simply the technology we use to measure blood flow, and in this context, we’re specifically looking at the umbilical artery, the vessel that carries blood from the baby back to the placenta. When a baby is measuring small, one possible reason is that the placenta isn’t functioning as well as it should. Checking flow in that artery gives us a window into how the placenta is handling that job.

A healthy placenta offers very little resistance, so blood moves through it easily, almost like a river flowing downhill. We measure this using a ratio comparing blood flow when the heart is pumping versus when it’s relaxed. When that ratio creeps up, we call it elevated flow, which is the first, mildest stage of an abnormal finding. If the placenta struggles more, we start to see flow briefly stop between heartbeats, which we call absent flow. In the most serious cases, the flow actually reverses direction. Each stage tells us not just that there’s likely a placental problem, but how urgent that problem is, which is exactly what shapes decisions about testing frequency and delivery timing.

To your specific question, Beth: yes, it’s absolutely true that something could happen between visits. That’s a real, if small, possibility for anyone in any pregnancy. What we’re really doing every time we set a follow-up interval is a kind of ongoing risk calculation. If everything looks reassuring, I might say come back in a week. If I’m a little more concerned, twice a week. If I’m genuinely worried, three times a week, like your care team chose for you. And if I ever feel that even daily visits in the office wouldn’t be frequent enough, that’s usually the point where delivery or hospital admission for closer monitoring becomes the right call.

There’s no strategy that removes all risk entirely. What we’re doing is narrowing that risk as much as we reasonably can and tailoring the plan to your specific situation, which in your case, with two babies and evolving Doppler findings, involved real complexity. Based on everything you’ve described, following you that closely and delivering around 34 weeks sounds like a very reasonable approach.

Learn More on the Healthful Woman Podcast

Dr. Fox answers several other listener questions in this episode, including why twins tend to grow smaller than singletons in the third trimester and whether that reflects a real problem or a normal adaptation, how cervical length and fetal fibronectin testing work together to estimate preterm birth risk in twin pregnancies, and whether pregnant women should consider checking their blood pressure at home to catch preeclampsia between routine visits. To hear the full conversation, listen to Mailbag 35 on the Healthful Woman podcast, produced by Maternal Fetal Medicine Associates.

Carnegie Imaging for Women blogs are intended for educational purposes only and do not replace certified professional care. Medical conditions vary and change frequently. Please ask your doctor any questions you may have regarding your condition to receive a proper diagnosis or risk analysis. Thank you!