Placenta praevia

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Placenta praevia
Other namesPlacenta previa
Placta prv.jpg
Diagram showing a placenta previa (Grade IV)
Specialty Obstetrics
Symptoms Bright red vaginal bleeding without pain [1]
Complications Mother: Bleeding after delivery [2]
Baby: Fetal growth restriction [1]
Usual onsetSecond half of pregnancy [1]
Risk factors Older age, smoking, prior cesarean section, labor induction, or termination of pregnancy [3] [4]
Diagnostic method Ultrasound [1]
Differential diagnosis Placental abruption [1]
Treatment Bed rest, cesarean section [1]
Frequency0.5% of pregnancies [5]

Placenta praevia is when the placenta attaches inside the uterus but in a position near or over the cervical opening. [1] Symptoms include vaginal bleeding in the second half of pregnancy. [1] The bleeding is bright red and tends not to be associated with pain. [1] Complications may include placenta accreta, dangerously low blood pressure, or bleeding after delivery. [2] [4] Complications for the baby may include fetal growth restriction. [1]

Contents

Risk factors include pregnancy at an older age and smoking as well as prior cesarean section, labor induction, or termination of pregnancy. [6] [3] [4] Diagnosis is by ultrasound. [1] It is classified as a complication of pregnancy. [1]

For those who are less than 36 weeks pregnant with only a small amount of bleeding recommendations may include bed rest and avoiding sexual intercourse. [1] For those after 36 weeks of pregnancy or with a significant amount of bleeding, cesarean section is generally recommended. [1] In those less than 36 weeks pregnant, corticosteroids may be given to speed development of the baby's lungs. [1] Cases that occur in early pregnancy may resolve on their own. [1]

Placenta praevia affects approximately 0.5% of pregnancies. [5] After four cesarean sections, however, it affects 10% of pregnancies. [4] Rates of disease have increased over the late 20th century and early 21st century. [3] The condition was first described in 1685 by Paul Portal. [7]

Signs and symptoms

Women with placenta previa often present with painless, bright red vaginal bleeding. This commonly occurs around 32 weeks of gestation, but can be as early as late mid-trimester. [8] More than half of women affected by placenta praevia (51.6%) have bleeding before delivery. [9] This bleeding often starts mildly and may increase as the area of placental separation increases. Placenta praevia should be suspected if there is bleeding after 24 weeks of gestation. Bleeding after delivery occurs in about 22% of those affected. [2]

Women may also present as a case of failure of engagement of fetal head. [10]

Cause

The exact cause of placenta previa is unknown. It is hypothesized to be related to abnormal vascularisation of the endometrium caused by scarring or atrophy from previous trauma, surgery, or infection. These factors may reduce differential growth of lower segment, resulting in less upward shift in placental position as pregnancy advances. [11]

Risk factors

Risk factors with their odds ratio [12]
Risk factor Odds ratio
Maternal age ≥ 40 (vs. < 20)9.1
Illicit drugs2.8
≥ 1 previous Cesarean section2.7
Parity ≥ 5 (vs. para 0)2.3
Parity 2–4 (vs. para 0)1.9
Smoking1.6
Congenital anomalies1.7
Male fetus (vs. female)1.1
Pregnancy-induced hypertension 0.4

The following have been identified as risk factors for placenta previa:

Placenta previa is itself a risk factor of placenta accreta. Alcohol use during pregnancy was previously listed as a risk factor, but is discredited by this article. [18]

Classification

Traditionally, four grades of placenta previa were used, [15] but it is now more common to simply differentiate between "major" and "minor cases. [19]

TypeDescription
MinorPlacenta is in lower uterine segment, but the lower edge does not cover the internal os
MajorPlacenta is in lower uterine segment, and the lower edge covers the internal os

Other than that placenta previa can be also classified as:

Complete: When the placenta completely covers the cervix

Partial: When the placenta partially covers the cervix

Marginal: When the placenta ends near the edge of the cervix, about 2 cm from the internal cervical os

Diagnosis

History may reveal antepartum hemorrhage. Abdominal examination usually finds the uterus non-tender, soft and relaxed. Leopold's maneuvers may find the fetus in an oblique or breech position or lying transverse as a result of the abnormal position of the placenta. Malpresentation is found in about 35% cases. [20] Vaginal examination is avoided in known cases of placenta previa. [15]

Confirmatory

Previa can be confirmed with an ultrasound. [21] Transvaginal ultrasound has superior accuracy as compared to transabdominal one, thus allowing measurement of distance between placenta and cervical os. This has rendered traditional classification of placenta previa obsolete. [22] [23] [24] [25]

False positives may be due to following reasons: [26]

In such cases, repeat scanning is done after an interval of 15–30 minutes.

In parts of the world where ultrasound is unavailable, it is not uncommon to confirm the diagnosis with an examination in the surgical theatre. The proper timing of an examination in theatre is important. If the woman is not bleeding severely she can be managed non-operatively until the 36th week. By this time the baby's chance of survival is as good as at full term.

Management

An initial assessment to determine the status of the mother and fetus is required. Although mothers used to be treated in the hospital from the first bleeding episode until birth, it is now considered safe to treat placenta previa on an outpatient basis if the fetus is at less than 30 weeks of gestation, and neither the mother nor the fetus are in distress. Immediate delivery of the fetus may be indicated if the fetus is mature or if the fetus or mother are in distress. Blood volume replacement (to maintain blood pressure) and blood plasma replacement (to maintain fibrinogen levels) may be necessary.

Corticosteroids are indicated at 24–34 weeks gestation, given the higher risk of premature birth. [1]

Delivery

The method of delivery is determined by clinical state of the mother, fetus and ultrasound findings. In minor degrees (traditional grade I and II), vaginal delivery is possible. RCOG recommends that the placenta should be at least 2 cm away from internal os for an attempted vaginal delivery. [27] When a vaginal delivery is attempted, consultant obstetrician and anesthetists are present in delivery suite. In cases of fetal distress and major degrees (traditional grade III and IV) a caesarean section is indicated. Caesarean section is contraindicated in cases of disseminated intravascular coagulation. An obstetrician may need to divide the anterior lying placenta. In such cases, blood loss is expected to be high and thus blood and blood products are always kept ready. In rare cases, hysterectomy may be required. [28]

Complications

Maternal

Fetal

Epidemiology

Placenta previa occurs approximately one of every 200 births globally. [5] It has been suggested that rates of placenta previa are increasing due to increased rates of Caesarean sections. [29] Reasons for regional variation may include ethnicity and diet. [5]

Africa

Rates of placenta praevia in sub-Saharan Africa are the lowest in the world, averaging 2.7 per 1000 pregnancies. Despite a low prevalence, this disease has had a profound impact in Africa as it is linked with negative outcomes for both the mother and infant. The most common maternal outcome of placenta praevia is extreme blood loss before or after birth (antepartum hemorrhage and postpartum hemorrhage), which is a major cause of maternal and infant mortality in countries like Tanzania. Risk factors for placenta praevia among African women include prior pregnancies, prenatal alcohol consumption, and insufficient gynecologic care. [30] In North Africa placenta praevia rates occur in 6.4 per 1000 pregnancies. [5]

Asia

Mainland China has the highest prevalence of placenta praevia in the world, [5] measuring at an average of 12.2 per 1000 pregnancies. Specifically, placenta praevia is most common in Southeast Asia, though the reason for this has not yet been investigated. There are many risk factors for placenta praevia in Asian women, of which include pregnancies occurring in women ages 35 and older (advanced maternal age) or in women who have had a prior Caesarean section, having multiple pregnancies, and experiencing either miscarriage or abortion in the past. In comparison with other Asian countries, placenta praevia is more common in Japan (13.9 per 1000) and Korea (15 per 1000). [5] In the Middle East, placenta praevia rates are lower in both Saudi Arabia (7.3 per 1000) and Israel (4.2 per 1000).

Australia

The continent with the second highest rates for placenta praevia is Australia, where it affects about 9.5 out of every 1000 pregnant women. [5] Researchers concerned with these rates have tested the specificity and sensitivity of fetal anomaly scans. In conclusion, it was determined the threshold that defines placenta praevia (based on proximity of placenta to cervix) must be reduced in order to improve the accuracy of diagnoses and to avoid false positives leading screenings. [31]

Europe

Placenta praevia in Europe occurs in about 3.6 per 1000 pregnancies. [32]

Latin America

In Latin America, placenta praevia occurs in about 5.1 per 1000 pregnancies. [5]

North America

In North America placenta praevia occurs in 2.9 per 1000 pregnancies. Ethnic differences indicate white women are less likely to experience placenta praevia than black women. Additionally, more cases of placenta praevia are found in women from low-income areas which are linked to insufficient pregnancy care. According to the socioeconomic demographic in North America, black women are more likely to come from low income areas and are thus more likely to develop placenta praevia. [5]

In Nova Scotia, infants born to pregnant woman who experience placenta praevia have a mortality rate 3–4 times higher than normal pregnancies. A couple of factors contribute to this rate, including length of time fetus was in the womb and mother's age. Infants that did survive experienced increased rates of birth defects, breathing problems, and blood abnormalities. [32]

Research suggests that the incidence of placenta praevia in the U.S. is increasing as a result of the increased rate of Caesarean sections. [33]

Related Research Articles

<span class="mw-page-title-main">Placental abruption</span> Medical condition

Placental abruption is when the placenta separates early from the uterus, in other words separates before childbirth. It occurs most commonly around 25 weeks of pregnancy. Symptoms may include vaginal bleeding, lower abdominal pain, and dangerously low blood pressure. Complications for the mother can include disseminated intravascular coagulopathy and kidney failure. Complications for the baby can include fetal distress, low birthweight, preterm delivery, and stillbirth.

Antepartum bleeding, also known as antepartum haemorrhage (APH) or prepartum hemorrhage, is genital bleeding during pregnancy after the 28th week of pregnancy up to delivery.

Bloody show or show is the passage of a small amount of blood or blood-tinged mucus through the vagina near the end of pregnancy. It is caused by thinning and dilation of the cervix, leading to detachment of the cervical mucus plug that seals the cervix during pregnancy and tearing of small cervical blood vessels, and is one of the signs that labor may be imminent. The bloody show may be expelled from the vagina in pieces or altogether and often appears as a jelly-like piece of mucus stained with blood. Although the bloody show may be alarming at first, it is not a concern of patient health after 37 weeks gestation.

Obstetrical bleeding is bleeding in pregnancy that occurs before, during, or after childbirth. Bleeding before childbirth is that which occurs after 24 weeks of pregnancy. Bleeding may be vaginal or less commonly into the abdominal cavity. Bleeding which occurs before 24 weeks is known as early pregnancy bleeding.

<span class="mw-page-title-main">Uterine rupture</span> Medical condition

Uterine rupture is when the muscular wall of the uterus tears during pregnancy or childbirth. Symptoms, while classically including increased pain, vaginal bleeding, or a change in contractions, are not always present. Disability or death of the mother or baby may result.

<span class="mw-page-title-main">Complications of pregnancy</span> Medical condition

Complications of pregnancy are health problems that are related to, or arise during pregnancy. Complications that occur primarily during childbirth are termed obstetric labor complications, and problems that occur primarily after childbirth are termed puerperal disorders. While some complications improve or are fully resolved after pregnancy, some may lead to lasting effects, morbidity, or in the most severe cases, maternal or fetal mortality.

<span class="mw-page-title-main">Abdominal pregnancy</span> Medical condition

An abdominal pregnancy is a rare type of ectopic pregnancy where the embryo or fetus is growing and developing outside the uterus, in the abdomen, and not in a fallopian tube, an ovary, or the broad ligament.

<span class="mw-page-title-main">Placenta accreta spectrum</span> Medical condition

Placenta accreta occurs when all or part of the placenta attaches abnormally to the myometrium. Three grades of abnormal placental attachment are defined according to the depth of attachment and invasion into the muscular layers of the uterus:

  1. Accreta – chorionic villi attached to the myometrium, rather than being restricted within the decidua basalis.
  2. Increta – chorionic villi invaded into the myometrium.
  3. Percreta – chorionic villi invaded through the perimetrium.

Postterm pregnancy is when a woman has not yet delivered her baby after 42 weeks of gestation, two weeks beyond the typical 40-week duration of pregnancy. Postmature births carry risks for both the mother and the baby, including fetal malnutrition, meconium aspiration syndrome, and stillbirths. After the 42nd week of gestation, the placenta, which supplies the baby with nutrients and oxygen from the mother, starts aging and will eventually fail. Postterm pregnancy is a reason to induce labor.

<span class="mw-page-title-main">Uterine atony</span> Loss of tone in the uterine musculature

Uterine atony is the failure of the uterus to contract adequately following delivery. Contraction of the uterine muscles during labor compresses the blood vessels and slows flow, which helps prevent hemorrhage and facilitates coagulation. Therefore, a lack of uterine muscle contraction can lead to an acute hemorrhage, as the vasculature is not being sufficiently compressed. Uterine atony is the most common cause of postpartum hemorrhage, which is an emergency and potential cause of fatality. Across the globe, postpartum hemorrhage is among the top five causes of maternal death. Recognition of the warning signs of uterine atony in the setting of extensive postpartum bleeding should initiate interventions aimed at regaining stable uterine contraction.

<span class="mw-page-title-main">Postpartum bleeding</span> Loss of blood following childbirth

Postpartum bleeding or postpartum hemorrhage (PPH) is often defined as the loss of more than 500 ml or 1,000 ml of blood following childbirth. Some have added the requirement that there also be signs or symptoms of low blood volume for the condition to exist. Signs and symptoms may initially include: an increased heart rate, feeling faint upon standing, and an increased breathing rate. As more blood is lost, the patient may feel cold, blood pressure may drop, and they may become restless or unconscious. The condition can occur up to six weeks following delivery.

<span class="mw-page-title-main">Vasa praevia</span> Condition in which fetal blood vessels cross or run near the internal opening of the uterus

Vasa praevia is a condition in which fetal blood vessels cross or run near the internal opening of the uterus. These vessels are at risk of rupture when the supporting membranes rupture, as they are unsupported by the umbilical cord or placental tissue.

Placental insufficiency or utero-placental insufficiency is the failure of the placenta to deliver sufficient nutrients to the fetus during pregnancy, and is often a result of insufficient blood flow to the placenta. The term is also sometimes used to designate late decelerations of fetal heart rate as measured by cardiotocography or an NST, even if there is no other evidence of reduced blood flow to the placenta, normal uterine blood flow rate being 600mL/min.

<span class="mw-page-title-main">Amniotic fluid embolism</span> Potentially fatal complication of pregnancy

An amniotic fluid embolism (AFE) is a life-threatening childbirth (obstetric) emergency in which amniotic fluid enters the blood stream of the mother, triggering a serious reaction which results in cardiorespiratory collapse and massive bleeding (coagulopathy). The rate at which it occurs is 1 instance per 20,000 births and it comprises 10% of all maternal deaths.

<span class="mw-page-title-main">Vaginal delivery</span> Delivery through the vagina

A vaginal delivery is the birth of offspring in mammals through the vagina. It is the most common method of childbirth worldwide. It is considered the preferred method of delivery, with lower morbidity and mortality than caesarean sections (C-sections).

An asynclitic birth or asynclitism are terms used in obstetrics to refer to childbirth in which there is malposition of the head of the fetus in the uterus, relative to the birth canal. Asynclitic presentation is different from a shoulder presentation, in which the shoulder is presenting first. Many babies enter the pelvis in an asynclitic presentation, and most asynclitism corrects spontaneously as part of the normal birthing process.

<span class="mw-page-title-main">Velamentous cord insertion</span> Velamentous placenta

Velamentous cord insertion is a complication of pregnancy where the umbilical cord is inserted in the fetal membranes. It is a major cause of antepartum hemorrhage that leads to loss of fetal blood and associated with high perinatal mortality. In normal pregnancies, the umbilical cord inserts into the middle of the placental mass and is completely encased by the amniotic sac. The vessels are hence normally protected by Wharton's jelly, which prevents rupture during pregnancy and labor. In velamentous cord insertion, the vessels of the umbilical cord are improperly inserted in the chorioamniotic membrane, and hence the vessels traverse between the amnion and the chorion towards the placenta. Without Wharton's jelly protecting the vessels, the exposed vessels are susceptible to compression and rupture.

<span class="mw-page-title-main">Circumvallate placenta</span> Medical condition

Circumvallate placenta is a rare condition affecting about 1-2% of pregnancies, in which the amnion and chorion fetal membranes essentially "double back" on the fetal side around the edges of the placenta. After delivery, a circumvallate placenta has a thick ring of membranes on its fetal surface. Circumvallate placenta is a placental morphological abnormality associated with increased fetal morbidity and mortality due to the restricted availability of nutrients and oxygen to the developing fetus.

Early pregnancy bleeding refers to vaginal bleeding before 14 weeks of gestational age. If the bleeding is significant, hemorrhagic shock may occur. Concern for shock is increased in those who have loss of consciousness, chest pain, shortness of breath, or shoulder pain.

The anomaly scan, also sometimes called the anatomy scan, 20-week ultrasound, or level 2 ultrasound, evaluates anatomic structures of the fetus, placenta, and maternal pelvic organs. This scan is an important and common component of routine prenatal care. The function of the ultrasound is to measure the fetus so that growth abnormalities can be recognized quickly later in pregnancy, to assess for congenital malformations and multiple pregnancies, and to plan method of delivery.

References

  1. 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 "Placenta Previa – Gynecology and Obstetrics – Merck Manuals Professional Edition". Merck Manuals Professional Edition. October 2017. Retrieved 9 December 2017.
  2. 1 2 3 Fan, D; Xia, Q; Liu, L; Wu, S; Tian, G; Wang, W; Wu, S; Guo, X; Liu, Z (2017). "The Incidence of Postpartum Hemorrhage in Pregnant Women with Placenta Previa: A Systematic Review and Meta-Analysis". PLOS ONE. 12 (1): e0170194. Bibcode:2017PLoSO..1270194F. doi: 10.1371/journal.pone.0170194 . PMC   5249070 . PMID   28107460.
  3. 1 2 3 Palacios-Jaraquemada, JM (April 2013). "Caesarean section in cases of placenta praevia and accreta". Best Practice & Research. Clinical Obstetrics & Gynaecology. 27 (2): 221–32. doi:10.1016/j.bpobgyn.2012.10.003. PMID   23127895.
  4. 1 2 3 4 Allahdin, S; Voigt, S; Htwe, TT (2011). "Management of placenta praevia and accreta". Journal of Obstetrics and Gynaecology. 31 (1): 1–6. doi:10.3109/01443615.2010.532248. PMID   21280984. S2CID   24852549.
  5. 1 2 3 4 5 6 7 8 9 10 Cresswell, JA; Ronsmans, C; Calvert, C; Filippi, V (June 2013). "Prevalence of placenta praevia by world region: a systematic review and meta-analysis". Tropical Medicine & International Health. 18 (6): 712–24. doi: 10.1111/tmi.12100 . PMID   23551357. S2CID   22138793.
  6. ↑ Karami, Manoochehr; Jenabi, Ensiyeh (28 July 2017). "Placenta previa after prior abortion: a meta-analysis". Biomedical Research and Therapy. 4 (7): 1071–1078. doi: 10.15419/bmrat.v4i07.197 . PMID   9396896.
  7. ↑ Baskett, Thomas F.; Calder, Andrew A.; Arulkumaran, Sabaratnam (2014). Munro Kerr's Operative Obstetrics E-Book. Elsevier Health Sciences. p. 178. ISBN   978-0-7020-5248-4.
  8. ↑ Callander, Kevin P. Hanretty; illustrated by Ian Ramsden, Robin (2004). Obstetrics illustrated (6th ed., Reprinted. ed.). Edinburgh [etc.]: Churchill Livingstone. p. 187. ISBN   978-0-443-07267-3.{{cite book}}: CS1 maint: multiple names: authors list (link)
  9. ↑ Fan, Dazhi; Wu, Song; Liu, Li; Xia, Qing; Wang, Wen; Guo, Xiaoling; Liu, Zhengping (9 January 2017). "Prevalence of antepartum hemorrhage in women with placenta previa: a systematic review and meta-analysis". Scientific Reports. 7: 40320. Bibcode:2017NatSR...740320F. doi:10.1038/srep40320. PMC   5220286 . PMID   28067303.
  10. 1 2 3 Brinsden, Judith Collier, Murray Longmore, Mark (2006). Oxford handbook of clinical specialties (7th ed.). Oxford: Oxford University Press. p. 1970. ISBN   978-0-19-853085-5.{{cite book}}: CS1 maint: multiple names: authors list (link)
  11. ↑ Dashe, JS; McIntire, DD; Ramus, RM; Santos-Ramos, R; Twickler, DM (May 2002). "Persistence of placenta previa according to gestational age at ultrasound detection". Obstetrics and Gynecology. 99 (5 Pt 1): 692–7. doi:10.1016/s0029-7844(02)01935-x. PMID   11978274. S2CID   23593594.
  12. ↑ Reece, E. Albert; Hobbins, John C., eds. (2006). Clinical obstetrics : the fetus and mother (3 ed.). Malden, MA: Blackwell Pub. p. 1050. ISBN   978-1-4051-3216-9.
  13. 1 2 3 4 Kendrick, Chantal Simon, Hazel Everitt, Tony (2005). Oxford handbook of general practice (2nd ed.). Oxford: Oxford University Press. p. 793. ISBN   978-0-19-856581-9.{{cite book}}: CS1 maint: multiple names: authors list (link)
  14. ↑ Weerasekera, D. S. (2000). "Placenta previa and scarred uterus — an obstetrician's dilemma". Journal of Obstetrics & Gynaecology. 20 (5): 484–5. doi:10.1080/014436100434659. PMID   15512632. S2CID   26268961.
  15. 1 2 3 Warren, Richard; Arulkumaran, Sabaratnam, eds. (2009). Best practice in labour and delivery (1st ed., 3rd printing. ed.). Cambridge: Cambridge University Press. pp.  142–146. ISBN   978-0-521-72068-7.
  16. ↑ Handler, A; Kistin, N; Davis, F; Ferré, C (Apr 15, 1991). "Cocaine use during pregnancy: perinatal outcomes". American Journal of Epidemiology. 133 (8): 818–25. doi:10.1093/oxfordjournals.aje.a115961. PMID   2021149.
  17. ↑ Kistin, N; Handler, A; Davis, F; Ferre, C (July 1996). "Cocaine and cigarettes: a comparison of risks". Paediatric and Perinatal Epidemiology. 10 (3): 269–78. doi:10.1111/j.1365-3016.1996.tb00050.x. PMID   8822770.
  18. ↑ Aliyu, MH; Lynch, O; Nana, PN; Alio, AP; Wilson, RE; Marty, PJ; Zoorob, R; Salihu, HM (July 2011). "Alcohol consumption during pregnancy and risk of placental abruption and placenta previa". Maternal and Child Health Journal. 15 (5): 670–6. doi:10.1007/s10995-010-0615-6. PMID   20437196. S2CID   30696061.
  19. ↑ "Placenta Praevia, Placenta Praevia Accreta and Vasa Praevia: Diagnosis and Management (Green-top Guideline No. 27)".
  20. ↑ Cotton, DB; Read, JA; Paul, RH; Quilligan, EJ (Jul 15, 1980). "The conservative aggressive management of placenta previa". American Journal of Obstetrics and Gynecology. 137 (6): 687–95. doi:10.1016/s0002-9378(15)33242-7. PMID   7395932.
  21. ↑ Bhide, Amar; Thilaganathan, Basky (2004). "Recent advances in the management of placenta previa". Current Opinion in Obstetrics and Gynecology. 16 (6): 447–51. doi:10.1097/00001703-200412000-00002. PMID   15534438. S2CID   24710500.
  22. ↑ Oppenheimer, LW; Farine, D; Ritchie, JW; Lewinsky, RM; Telford, J; Fairbanks, LA (October 1991). "What is a low-lying placenta?". American Journal of Obstetrics and Gynecology. 165 (4 Pt 1): 1036–8. doi:10.1016/0002-9378(91)90465-4. PMID   1951509.
  23. ↑ Neale, E. J.; Rogers, M. S. (1 July 1989). "Vaginal ultrasound for ruling out placenta previa. Case report". BJOG: An International Journal of Obstetrics and Gynaecology. 96 (7): 881–2. doi:10.1111/j.1471-0528.1989.tb03334.x. PMID   2669937. S2CID   7724217.
  24. ↑ Smith, RS; Lauria, MR; Comstock, CH; Treadwell, MC; Kirk, JS; Lee, W; Bottoms, SF (January 1997). "Transvaginal ultrasonography for all placentas that appear to be low-lying or over the internal cervical os". Ultrasound in Obstetrics & Gynecology. 9 (1): 22–4. doi: 10.1046/j.1469-0705.1997.09010022.x . PMID   9060125. S2CID   44809710.
  25. ↑ Farine, D; Fox, HE; Jakobson, S; Timor-Tritsch, IE (September 1988). "Vaginal ultrasound for diagnosis of placenta previa". American Journal of Obstetrics and Gynecology. 159 (3): 566–9. doi:10.1016/s0002-9378(88)80009-7. PMID   3048096.
  26. ↑ Sutton, David (2003). Textbook of radiology and imaging (7th ed.). Edinburgh: Churchill Livingstone. pp.  1064. ISBN   978-0-443-07109-6.
  27. ↑ "Placenta Previa, Placenta Previa Accreta and Vasa Previa: Diagnosis and Management" (PDF). RCOG Guidelines — Green-top 27. Retrieved 20 August 2020.
  28. ↑ Kayem, G; Davy, C; Goffinet, F; Thomas, C; Clément, D; Cabrol, D (September 2004). "Conservative versus extirpative management in cases of placenta accreta". Obstetrics and Gynecology. 104 (3): 531–6. doi:10.1097/01.AOG.0000136086.78099.0f. PMID   15339764. S2CID   25440874.
  29. ↑ Miller, DA; Chollet, JA; Goodwin, TM (July 1997). "Clinical risk factors for placenta previa-placenta accreta". American Journal of Obstetrics and Gynecology. 177 (1): 210–4. doi:10.1016/s0002-9378(97)70463-0. PMID   9240608.
  30. ↑ Senkoro, Elizabeth Eliet; Mwanamsangu, Amasha H.; Chuwa, Fransisca Seraphin; Msuya, Sia Emmanuel; Mnali, Oresta Peter; Brown, Benjamin G.; Mahande, Michael Johnson (2017). "Frequency, Risk Factors, and Adverse Fetomaternal Outcomes of Placenta Previa in Northern Tanzania". Journal of Pregnancy. 2017: 5936309. doi: 10.1155/2017/5936309 . ISSN   2090-2727. PMC   5339534 . PMID   28321338.
  31. ↑ Olive, E. C.; Roberts, C. L.; Nassar, N.; Algert, C. S. (2006-11-23). "Test characteristics of placental location screening by transabdominal ultrasound at 18-20 weeks". Ultrasound in Obstetrics & Gynecology. 28 (7): 944–949. doi: 10.1002/uog.3873 . ISSN   0960-7692. PMID   17121427. S2CID   42163376.
  32. 1 2 Crane, J (2004). "Neonatal outcomes with placenta previa". Obstetrics & Gynecology. 93 (4): 541–544. doi:10.1016/s0029-7844(98)00480-3. ISSN   0029-7844. PMID   10214830.
  33. ↑ Goodwin, T. Murphy; Chollet, Janet A.; Miller, David A. (1997-07-01). "Clinical risk factors for placenta previa–placenta accreta". American Journal of Obstetrics & Gynecology. 177 (1): 210–214. doi:10.1016/S0002-9378(97)70463-0. ISSN   1097-6868. PMID   9240608.
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