Most of what goes wrong in childbirth goes wrong in labor, and the record that matters is the one written that day. Vasa previa is the rare exception. Its outcome is usually decided months earlier, in a quiet ultrasound room at around twenty weeks — by whether anyone looked.
It is visible on ultrasound in the great majority of cases, it has a well-described set of risk factors, and it has an intervention — a planned cesarean before labor begins — that works very nearly all the time. The cruelty of an undiagnosed vasa previa is that the pregnancy looks normal until the membranes rupture, and by then the window has closed. This is a guide for parents told after the fact: what the prenatal records should contain, what the guidelines say, and how a missed diagnosis is reconstructed from paper.
What Is Vasa Previa?
Vasa previa is a condition in which unprotected fetal blood vessels run through the membranes across or very near the cervix — the exact path the baby must travel to be born. In a normal pregnancy every fetal vessel is armored: bundled inside the umbilical cord and its protective jelly, or embedded in the body of the placenta. In vasa previa, one or more vessels leave that protection and cross the cervix with nothing around them but a thin sheet of membrane. The Society for Maternal-Fetal Medicine, in Consult Series #37, describes vasa previa as occurring in roughly 1 in 2,500 deliveries.
Clinicians classify it by why the vessels are exposed. Type I — the most common, and the one that matters most here — arises from a velamentous cord insertion, where the cord attaches to the membranes instead of the placenta. Type II involves vessels bridging two lobes of a bilobed or succenturiate placenta; Type III, an aberrant vessel looping over the cervix from the placental edge.
Why Is Vasa Previa So Dangerous at Delivery?
Vasa previa is dangerous because the blood at risk belongs to the baby, and a baby has very little of it to lose. When the membranes rupture — on their own or when a clinician breaks them — a vessel crossing the cervix can tear with them, and what follows is fetal hemorrhage, not maternal bleeding. A newborn's total blood volume is only a small fraction of an adult's — on the order of a cup and a half for an average full-term baby — so losing even a modest amount is catastrophic, and it happens in minutes rather than hours.
The classic presentation is painless vaginal bleeding when the membranes break, followed immediately by a collapsing fetal heart rate — often a sinusoidal pattern or severe bradycardia. Because it resembles far more common causes of third-trimester bleeding, it can be misread as a placental abruption or as bloody show. The distinction is urgent: with fetal exsanguination the useful clock runs in minutes, not against the familiar thirty-minute decision-to-incision benchmark.
How Much Does Prenatal Diagnosis Change the Outcome?
More than almost any other single decision in obstetrics. The landmark multicenter study, led by Dr. Yinka Oyelese and published in Obstetrics & Gynecology in 2004, assembled 155 cases confirmed by pathology or photographs. Where vasa previa was diagnosed prenatally, 59 of 61 babies survived — about 97%. Where it was not, 41 of 94 survived — about 44%.
The reason the gap is so large is worth sitting with: nothing about the treatment after the bleeding starts is better in the diagnosed group. The diagnosis itself is the treatment. Knowing about vasa previa allows a scheduled cesarean before the membranes can rupture, so the hemorrhage never occurs. The entire protective plan depends on a finding made months in advance.
Those figures are now more than twenty years old, and the objection that they came partly from a voluntary case registry is a fair one. The newer evidence is stronger, not weaker. A 2025 systematic review and meta-analysis in the American Journal of Obstetrics & Gynecology, led by Dr. Bridget Donovan with Dr. Oyelese among the co-authors, pooled 19 cohort studies covering 779,845 pregnancies in which a standardized second-trimester screening protocol was actually in place. Among the 505 confirmed cases of vasa previa, 494 — 97.8% — were identified before birth. Pooled sensitivity and specificity were both 1.00, with just 11 false positives across roughly 775,000 pregnancies, and pooled perinatal survival among the prenatally diagnosed reached 98.15%. Where hospitals look for vasa previa systematically, they find very nearly all of it — and almost every one of those babies lives.
What Should the Second-Trimester Anatomy Scan Have Documented?
The single most useful line in a prenatal record, for this question, is the one describing where the umbilical cord attaches to the placenta — the placental cord insertion site. Parents rarely know to look for it, but it is often there. The AIUM Practice Parameter for Standard Diagnostic Obstetric Ultrasound Examinations, developed jointly with ACR, ACOG, SMFM, and the Society of Radiologists in Ultrasound, includes documenting that site in a standard second- or third-trimester examination when technically possible.
On a report, that line typically reads “placental cord insertion: central,” or eccentric, marginal, velamentous, or sometimes “not visualized.” A velamentous insertion is the finding that should prompt a closer look, because Type I vasa previa grows directly out of it. A blank or “not visualized” entry is not automatically a failure, but it opens a question: if the cord insertion could not be seen, was anything scheduled to see it later?
The 2024 international expert consensus on vasa previa, published in the American Journal of Obstetrics & Gynecology after a Delphi survey of an international expert panel, reached agreement on 26 statements. Among them: the placental cord insertion should be examined and a color flow Doppler sweep performed over the area above the cervix at the second-trimester anatomy scan in all pregnant patients. Where a low-lying placenta or placenta previa is found in the second trimester, the panel recommended a transvaginal ultrasound with Doppler at approximately 32 weeks to rule out vasa previa. For known, asymptomatic vasa previa, it recommended scheduled cesarean delivery between 35 and 37 weeks.
Why Do Guidelines Still Disagree About Screening?
Because they do — and any honest account of a missed vasa previa case has to say so. A 2026 analysis in Ultrasound in Obstetrics and Gynecology by Agudogo, McMahon, Rolnik, and Oyelese compared obstetric imaging guidelines from 15 countries plus two international ISUOG guidelines. Of the 22 reviewed, only 12 mentioned vasa previa at all, and none explicitly recommended routine screening for it in all pregnant patients. Nine recommended assessing the placental cord insertion, and only five national societies had a dedicated vasa previa guideline. The authors concluded that guidelines have not caught up to the evidence that structured screening works.
That finding cuts both ways. A defense will lean on it directly: no major United States body mandates universal vasa previa screening, so a sonographer who performed no Doppler sweep over the cervix in a low-risk patient broke no written rule. That has real force in a genuinely low-risk pregnancy with an unremarkable scan. It has much less force in the cases that actually get filed, which almost never involve a patient with no risk factors — they involve a chart that already contained a velamentous cord insertion, a low-lying placenta, a bilobed placenta, an IVF conception, or a twin pregnancy. No screening mandate is needed to answer what should follow a finding already written down.
When Does a Missed Vasa Previa Point to Possible Negligence?
Vasa previa can be missed without anyone having been careless. A birth injury review does not ask whether the condition existed — it asks whether the information available at the time was handled the way the standard of care required. The deciding questions are concrete:
- Did the chart contain a documented risk factor — velamentous cord insertion, low-lying placenta, bilobed placenta, IVF conception, multiple gestation — and did any note show someone acted on it?
- Was the placental cord insertion site documented on the anatomy scan, or was that line blank with no plan to revisit it?
- When a low-lying placenta was found in the second trimester and later called resolved, was the follow-up transvaginal ultrasound with Doppler actually performed — or did “resolved” end the inquiry?
- Once vasa previa was known, was a scheduled cesarean planned in the recommended window, or was the patient allowed to reach labor?
- When bleeding began alongside a deteriorating fetal heart rate, how many minutes passed before delivery, and was fetal blood loss ever considered as the cause?
Where the answers show no warning signs and a team that moved as fast as the anatomy allowed, a devastating outcome reflects the limits of medicine. Where they show a velamentous cord insertion sitting in a chart nobody revisited, the injury traces back not to the vessels but to the look that was never taken.
What a Trained Reader Looks For in the Records
A vasa previa case is unusual in that its most important evidence predates the delivery by months. When Herb Borroto, M.D., J.D., the firm's Medical-Legal Expert, reviews a file like this, the reading runs both directions from the birth:
- Every prenatal ultrasound report in full, and the follow-up orders. Not just the impression line, but placental location, the cord insertion description, whether Doppler was used, and whether an ordered follow-up ever happened.
- The stored images, not only the reports. Where images are preserved, an examiner can sometimes see vessels crossing the cervix on a study whose report said nothing about them. That gap between what was captured and what was written is often the center of the case.
- The placental pathology report. The pathologist's description documents the velamentous insertion, the extra lobe, or the torn vessel — retrospective proof of what the prenatal scan was looking at.
- The delivery timeline to the minute. Rupture of membranes, onset of bleeding, heart rate changes, the incision, and the newborn's first cord blood gas and hemoglobin — the numbers showing how much blood was lost, and when.
Alex Alvarez, the firm's Managing Partner and a Board Certified Civil Trial Lawyer, presents these cases along the line the medicine itself draws. The fight is rarely about whether vasa previa is dangerous; everyone agrees it is. It is about a chart that already held the clue, a follow-up study nobody ordered, and the fact that the difference between a scheduled cesarean and a 3 a.m. emergency was available to be known months in advance.
If Your Baby Was Injured by an Undiagnosed Vasa Previa
If your baby was diagnosed with vasa previa only at or after delivery — and suffered severe blood loss, needed transfusion, developed a brain injury, or did not survive — the answers are largely in records you may never have seen: the full prenatal ultrasound reports, the stored images, the follow-up orders, and the placental pathology. A free, confidential case review can help you understand whether the prenatal care met the standard those findings called for, and whether your state's filing deadlines remain open. See our related guides to placental abruption, HIE and birth asphyxia, fetal monitoring failures, infant wrongful death claims, and the birth injury statute of limitations.
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Sources
- Oyelese Y, et al. — “Vasa Previa: The Impact of Prenatal Diagnosis on Outcomes,” Obstetrics & Gynecology (2004), on 155 pathology-confirmed cases and survival of 59 of 61 infants with prenatal diagnosis versus 41 of 94 without. pubmed.ncbi.nlm.nih.gov
- Donovan B, Bonanni G, Javinani A, et al. — “Ultrasound screening for vasa previa: a systematic review and meta-analysis,” American Journal of Obstetrics & Gynecology (2025), on 19 cohort studies covering 779,845 pregnancies, prenatal detection of 494 of 505 confirmed cases (97.8%), pooled sensitivity and specificity of 1.00, and pooled perinatal survival of 98.15% among prenatally diagnosed cases. pubmed.ncbi.nlm.nih.gov
- Society for Maternal-Fetal Medicine — Consult Series #37, “Diagnosis and management of vasa previa,” on incidence, diagnostic approach, antenatal corticosteroid timing, hospitalization considerations, and delivery timing. publications.smfm.org
- “Vasa previa in singleton pregnancies: diagnosis and clinical management based on an international expert consensus,” American Journal of Obstetrics & Gynecology (2024), on the 26 consensus statements, second-trimester color Doppler assessment over the cervix, transvaginal follow-up at approximately 32 weeks after a low-lying placenta, and scheduled cesarean delivery between 35 and 37 weeks. ajog.org
- Agudogo S, McMahon C, Rolnik DL, Oyelese Y — “Vasa previa screening: comparison of national and international obstetric imaging guidelines,” Ultrasound in Obstetrics and Gynecology (2026), on 22 guidelines from 15 countries plus two ISUOG guidelines, of which only 12 mentioned vasa previa and none explicitly recommended routine screening. pubmed.ncbi.nlm.nih.gov
- AIUM–ACR–ACOG–SMFM–SRU — “AIUM Practice Parameter for the Performance of Standard Diagnostic Obstetric Ultrasound Examinations,” Journal of Ultrasound in Medicine, on documentation of the placental cord insertion site as part of a standard second- or third-trimester examination when technically possible. onlinelibrary.wiley.com