If you've never challenged an escape room, the concept is likely precisely what you think - you're locked inside a room and need to escape. However, you'll encounter challenges along the way. You'll have to solve riddles and puzzles to get to the next clue, and this process continues until you can unlock the door and let yourself out.
Picture yourself in one of these rooms. While you're playing, a feature of the room breaks and the exit door becomes blocked by an obstacle. This obstacle makes it impossible to leave the way you came. Eventually, the Escape Room Team realizes you're totally stuck and cuts a hole in the wall to get you out. Not only does this make for a good story, but you've also experienced what it's like to be on the other side of Placenta Previa.
A placenta previa occurs when the placenta develops over the entire cervical opening, which makes it impossible for the baby to be born vaginally. A cesarian section must be performed.
However, that's the end of the story. Let's go back to the beginning and figure out how and why this problem occurs in the first place! We'll also look at some must-know diagnostic and management info along the way!
The Placenta
It all started when your parents loved each other very much. erm, actually. Scratch that. Perhaps we've gone too far back. Let's fast forward to the part where the placenta finds a place to start forming in the womb.
The placenta wants to connect to the uterine wall at a location that allows good communication between the two. It will typically connect at a location away from the cervical opening and away from any scars or problem areas the uterine wall may have. If the uterus has no scarring or other issues, the chances that the placenta will connect properly are pretty good (chances of developing placenta previa are below 1%). However, if the uterine wall has scars from previous cesarian sections, this limits the locations to which the placenta can attach and increases the likelihood that the placenta will form over the cervical opening. Looking at several different sources, it seems that the chance a placenta previa will form in the pregnancy following a cesarian delivery increases by ~40-60% (Cresswell et al., 2013).
Previous cesarian section deliveries are not the only risk factor for developing placenta previa. According to Salim and Satti (2021), some of the others include:
Uterine Surgery
Increased Maternal age (>35 years old)
High Parity
Multiple Fetal Gestation
Smoking / Drug use
The mechanism for the placenta forming in a less-than-ideal place is that scars leave poorly vascularized areas of the uterine wall. This causes the placenta to look elsewhere for an attachment site with better circulation.
The good news is that most placenta previa cases resolve independently (~90% of them) (Getahun et al., 2006). Some portion of the placenta may be over or near the cervical os, but as the uterus grows throughout the pregnancy, the placenta previa can resolve on its own. For our discussion here, we'll focus on the placenta previa that does not resolve independently. These are the patients who will need cesarian delivery and are at high risk for hemorrhage.
To further understand the spectrum of placenta previa, let's discuss the two main determining factors involved - placental coverage of the cervix and the depth of placental adhesion.
Coverage and Depth
A placenta previa can vary in how much of the cervical opening it covers and how deeply the placenta is attached to the uterine wall. We'll refer to these as:
Coverage (how much covers the cervical opening)
Depth (how deeply it attaches to the uterine wall)
When discussing cervix coverage, four classifications are usually referred to. Of note, "Marginal" and "Partial" help describe the position of the placenta, but they are somewhat outdated due to these classifications being associated with digital exams.
Low-lying Placenta: The placenta is positioned low in the uterus without reaching the cervix.
Marginal Previa: The placenta's edge is close to but does not cover the cervix.
Partial Previa: The placenta partially covers the cervix.
Complete Previa: The Placenta fully obstructs the cervical opening.
The proximity of the placenta to the cervix will change in many cases due to atrophy of the occluding edge of the placenta or growth of the uterus as pregnancy continues. These are diagnosed and monitored under ultrasound exam (digital exam can cause hemorrhage).
Now that we understand the degree of cervical coverage and how it can change over time, let's discuss the depth of placental adhesion (this can be pathological in placenta previa and lead to severe complications).
Not only can the placenta cover the cervix, it can be adhered to the uterine wall too deeply. The Placenta Accreta Spectrum Disorders (Accreta, Increta, Percreta) are used to describe how deeply the placenta is secured. These disorders raise the risk of severe bleeding and may require complex surgical solutions, including hysterectomy at the time of cesarian delivery.
Placenta Accreta: The placenta attaches too deeply into the endometrium (the inner lining of the uterus) but does not penetrate the myometrium (the muscular layer of the uterus).
Placenta Increta: The placenta invades the myometrium, indicating a deeper and more problematic level of attachment.
Placenta Percreta: The placenta penetrates through the uterine wall and can attach to other organs, such as the bladder.
How common are PAS disorders? There is a study by Silver et al. (2006) which compared the number of cesarean births to the percent of PAS occurrence. This is what they found:
1st cesarean birth: PAS in 3%
2nd cesarean birth: PAS in 11%
3rd cesarean birth: PAS in 40%
4th cesarean birth: PAS in 61%
5th cesarean birth: PAS in 67%
You're likely catching on to the theme of uterine wall abnormalities leading to placental complications of depth and coverage.
Presentation and Diagnosis
Placenta Previa has a very convenient acronym to help remember its presentation: PREVIA.
P = Painless, bright red bleeding.
Due to the location of the bleeding (near the cervical os), the blood will likely enter the cervix and present with vaginal bleeding.
R = Relaxed, soft uterus that is non-tender.
Blood is an irritant, but since it does not make much contact with the uterine wall, it is less likely to cause pain. The bleeding primarily comes from the intervillous, which is maternal blood. However, fetal blood from terminal villi can be lost if the sheering disruption of vessels is more severe. In some cases, cramping and contractions may be reported by the patient.
E = Episodes of bleeding that range from mild to profuse
Approximately 90% of placenta previa patients experience an episode of bleeding at some point. The frequency and severity of bleeding are correlated with the likelihood of complications.
V = Visible Bleeding
Vaginal bleeding should be apparent because of the location of the bleed - near the cervix.
I = Intercourse Bleeding
For the same reason that digital exams are not performed in placenta previa, sexual intercourse may need to be avoided if the patient is experiencing episodes of bleeding.
A = Abnormal Fetal Position
The placenta is pretty big, and so is the head of the baby. These two relatively large items inside the womb will likely not occupy the same space. Thus, the baby may be in a transverse lie or a breech position.
Now that we know how it presents, how is it actually diagnosed? Imaging. A maternal ultrasound or MRI can detect a previa and avoid unnecessary digital exams that could cause hemorrhage (Anderson-Bagga & Sze, 2023). While the presentation can provide substantial clues that a placenta previa may be present, imaging is required to confirm the diagnosis. After diagnosis is confirmed, how is placenta previa treated?
Treatment
Although our focus is usually on acutely unstable patients, most cases of placenta previa resolve with time. Approximately 90 percent of placenta previa cases identified on ultrasound examination at ~20 weeks of gestation resolve independently before delivery at term- which is excellent news! The cervix becomes unobstructed as the uterus grows, and the placenta searches for better vasculature (Oyelese & Smulian, 2006). For the remaining ~10%, however, the cervix may remain occluded. How can we help these patients?
The only real fix for placenta previa is cesarean delivery and possible hysterectomy if the patient has PAS. However, we may need to temporize the patient before they can get to an operating room. This is where intrauterine resuscitation comes into play.
Intrauterine resuscitation (IUR) is a list of actions that can help with maternal stabilization (which is the best way to aid in fetal stabilization). Here are the line items that are probably applicable to placenta previa (Simpson & James, 2005):
Position (Left Lateral Recumbent)
Remember supine hypotension syndrome? The womb can lay very heavily on the inferior vena cava (IVC), which runs along the patient's right side of their abdomen. When too much weight compresses the IVC, cardiac preload can be impaired. Lower preload means lower cardiac output, which we must fix. Tilting the patient's hips to their left helps transfer this weight off the IVC and onto their aorta, which has a much higher pressure. For reference, the IVC may hover somewhere around 5 mmHg (~CVP), while the aorta will be pressurized around whatever the MAP is (hopefully above 65 mmHg at least).
A hands-and-knees position can also be considered if fetal heart rate tracings show signs of concern, such as prolonged/variable decelerations or bradycardia.
Volume
If the patient is showing signs of hypovolemia (tachycardia, tachypnea, weakness, diaphoresis, etc.), volume resuscitation is necessary. Volume resuscitation may be as simple as a 500mL bolus of crystalloids or as complex as a massive blood transfusion protocol being activated. Volume is critical, especially if the patient needs blood products. Ensure you have large-bore IV access. The goal is maintaining a hemoglobin value >10 g/dL (while hemoglobin is not the only important measurement, it is heavily weighted). The patient should be resuscitated until they no longer show signs of hypovolemia and (if applicable to you) fetal heart race tracings improve.
Tocolysis
Although not routinely or empirically used in all cases of placenta previa, a tocolytic may be helpful in situations in which it is believed the contraction of the uterus is causing further bleeding (seek consultation).
Also, here is an excerpt from Wikipedia for everyone in my class who was wondering where the term "Tocolytic" comes from: "Tocolytics (also called anti-contraction medications or labor suppressants) are medications used to suppress premature labor (from Greek τόκος tókos, “childbirth," and λύσις lúsis, "loosening")."
What about Oxygen?
If there is maternal hypoxemia, shortness of breath, air hunger, etc., oxygen is indicated. However, what about the routine use of oxygen without these items? In their 2021 systematic review and meta-analysis, Raghuraman et al. investigated "Maternal Oxygen Supplementation Compared With Room Air for Intrauterine Resuscitation." - you can find it here: https://doi.org/10.1001/jamapediatrics.2020.5351
I'll state again that this literature is about non-hypoxemic patients. The article is worth looking at, but in case you don't, they concluded that there was no measurable difference in key fetal health measurements with or without supplemental oxygen unless the mother was hypoxemic.
Conclusion
Sifting through OB literature is a lengthy process. In researching this blog, I found that there are a lot of special considerations for what the OB unit does regarding monitoring, care algorithms, exams, consultation, etc. It's difficult not to get lost in the details. However, in everything I read, I think the most critical aspects for EMS to know about placenta previa are as follows:
1: Your exam needs to be sensitive to placenta previa. Remember the PREVIA acronym and what type of history leads you towards the working diagnosis of a placenta previa. The last thing you want is a delay in this patient (and fetus) getting to an OR if they are sick and bleeding.
2: Know intrauterine resuscitation, at least up to your capabilities. While you may not be starting a massive transfusion protocol in the back of your ambulance, you can identify the need for positioning, volume, and potentially oxygen and tocolytics (always consult when needed).
3: Don't make things worse. Attempting digital examination and causing more trauma to a bleeding placenta is bad, but triaging this patient to the wrong hospital could be deadly.
Thanks for reading!
btw - stay tuned for new episodes in FOAMfrat Studio (and the podcast) Featuring Demi Wilkes! We're releasing a series called OB Icebergs, where we examine surface (10%) vs. deeper (90%) knowledge in OB emergencies. The first episode will be released soon, and the topic is Placenta Previa!
References
American College of Obstetricians and Gynecologists, & Society for Maternal–Fetal Medicine. (2018, December). Placenta Accreta Spectrum. Obstetric Care Consensus, (7).
Anderson-Bagga, F. M., & Sze, A. (2023, June 12). Placenta Previa. In StatPearls [Internet]. Treasure Island (FL): StatPearls Publishing. Available from https://www.ncbi.nlm.nih.gov/books/NBK539818/
Bonnar, J. (2000). Massive obstetric haemorrhage. Bailliere's Best Practice & Research in Clinical Obstetrics & Gynaecology, 14(1) (graph)
Cresswell, J. A., Ronsmans, C., Calvert, C., & Filippi, V. (2013). Prevalence of placenta praevia by world region: a systematic review and meta-analysis. Tropical medicine & international health : TM & IH, 18(6), 712–724. https://doi.org/10.1111/tmi.12100
Faiz, A. S., & Ananth, C. V. (2003). Etiology and risk factors for placenta previa: an overview and meta-analysis of observational studies. The journal of maternal-fetal & neonatal medicine : the official journal of the European Association of Perinatal Medicine, the Federation of Asia and Oceania Perinatal Societies, the International Society of Perinatal Obstetricians, 13(3), 175–190. https://doi.org/10.1080/jmf.13.3.175.190
Fan, D., Wu, S., Liu, L., Xia, Q., Wang, W., Guo, X., & Liu, Z. (2017). Prevalence of antepartum hemorrhage in women with placenta previa: a systematic review and meta-analysis. Scientific reports, 7, 40320. https://doi.org/10.1038/srep40320
Getahun, D., Oyelese, Y., Salihu, H. M., & Ananth, C. V. (2006). Previous cesarean delivery and risks of placenta previa and placental abruption. Obstetrics and gynecology, 107(4), 771–778. https://doi.org/10.1097/01.AOG.0000206182.63788.80
Oyelese, Y., & Smulian, J. C. (2006). Placenta previa, placenta accreta, and vasa previa. Obstetrics and Gynecology, 107(4), 927–941. https://doi.org/10.1097/01.AOG.0000207559.15715.981.
Salim, N. A., & Satti, I. (2021). Risk factors of placenta previa with maternal and neonatal outcome at Dongola/Sudan. Journal of family medicine and primary care, 10(3), 1215–1217. https://doi.org/10.4103/jfmpc.jfmpc_2111_20
Silver, R. M., Landon, M. B., Rouse, D. J., Leveno, K. J., Spong, C. Y., Thom, E. A., Moawad, A. H., Caritis, S. N., Harper, M., Wapner, R. J., Sorokin, Y., Miodovnik, M., Carpenter, M., Peaceman, A. M., O'Sullivan, M. J., Sibai, B., Langer, O., Thorp, J. M., Ramin, S. M., Mercer, B. M., … National Institute of Child Health and Human Development Maternal-Fetal Medicine Units Network (2006). Maternal morbidity associated with multiple repeat cesarean deliveries. Obstetrics and gynecology, 107(6), 1226–1232. https://doi.org/10.1097/01.AOG.0000219750.79480.84
Simpson KR, James DC. Efficacy of intrauterine resuscitation techniques in improving fetal oxygen status during labor. Obstet Gynecol 2005; 105:1362.
Raghuraman, N., Temming, L. A., Doering, M. M., Stoll, C. R., Palanisamy, A., Stout, M. J., Colditz, G. A., Cahill, A. G., & Tuuli, M. G. (2021). Maternal Oxygen Supplementation Compared With Room Air for Intrauterine Resuscitation: A Systematic Review and Meta-analysis. JAMA pediatrics, 175(4), 368–376. https://doi.org/10.1001/jamapediatrics.2020.5351