Operative vaginal delivery

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Operative vaginal delivery
Diagram of Instrumental Assisted Birth.jpg
Nine diagrams illustrating breech and natural births and the obstetrical instruments used to assist them circa 1800s
Specialty Obstetrics

Operative vaginal delivery, also known as assisted or instrumental vaginal delivery, is a vaginal delivery that is assisted by the use of forceps or a vacuum extractor. [1]

Contents

Operative vaginal delivery is required in times of maternal or fetal distress to assist in childbirth as an alternative to caesarean section. [2] Its use has decreased over the years in comparison to caesarean section. [2] [3] The two main instruments used are rotational forceps and vacuum extractors, each with different complication risks. Possible complications introduced with the use of instruments for the mother include pelvic floor injury, anal sphincter injury, bleeding, or cuts. [4] [5] Possible complications to the infant include bruising to the scalp, retinal bleeding, and scrapes to the scalp and face. [5] [6]

Indications

When fetal distress occurs during the second stage of labor, operative vaginal delivery may be used in place of caesarean section which may pose additional risks after birth has progressed and the fetal head is deep in the birth canal. Maternal exhaustion and fetal distress would also be indications for appropriate use of operative vaginal delivery. [2]

An analysis of multiple studies found that detecting the angle of the fetal head using an ultrasound is a reliable way to predict where uncomplicated operative vaginal delivery can be used, especially in first-time mothers. [7]

Contraindications

Definite contraindication include non-engagement of the fetal head, unknown fetal position, cervix not fully dilated, membranes not ruptured, known loss of minerals from fetal bone, and fetal disorders. [8]

Relative contraindication include less than 34 weeks of pregnancy, and less than 2400 grams of the total fetal weight.[ medical citation needed ]

Benefits

Discharge from the hospital after operative vaginal delivery (2–3 days) is faster than after a caesarean section, which requires 4 days for discharge. It is suggested that this decrease in in-hospital recovery time reflects a decrease in pain and an increase in post-birth mobility for the mother. [9] Using operative vaginal delivery avoids the risks associated with repeat caesarian sections or vaginal births after caesarian sections for women who want to have additional pregnancies. [9] Compared to caesarean section, operative vaginal delivery have been more beneficial, and has been recognized to have a reduction in complications such as death, venous thromboembolism, costs of procedure, time of recovery and infection. [10]

Complications

Pelvic floor injury

The process of operative vaginal delivery can cause damage to the pelvic floor and anal sphincter. Obstetric anal sphincter injury (OASI) is a complication that can lead to short term morbidity and long term loss of bowel movement control. OASI is observed in about 5.7% of first time mothers and 1.5% in people who have given birth before with no prior OASI. [4] In an 8-year study done at sub-Saharan hospitals, out of 100,307 vaginal deliveries, 2.1% resulted in OASI with forceps delivery found to have a higher incidence rate of 8.6% compared to 1.3% in normal vaginal deliveries. [11]

While there does not appear to be a difference in long-term bowel or pelvic floor-related symptoms, studies of deliveries using forceps appear to show an association with being at an increased risk of long-term fecal incontinence. [12] Forceps also have been shown to cause facial injury to the fetus and further significant injury to the mother via third‐ or fourth‐degree tears, vaginal trauma, and fecal incontinence. Although vacuum extractions can cause less injuries to the mother, it can cause more injury to the fetus via scalp injury and cephalhaematoma. [6] Studies suggest that performing a episiotomy can reduce the risk of OASI in both forceps and vacuum-assisted deliveries. [13]

Additionally, operative vaginal delivery increases the risk for postpartum hemorrhage and venous thromboembolism. [5]

Post traumatic stress disorder

While statistics specific to PTSD following operative vaginal delivery are not available, studies show that 3-4% of all women and 20% of women in high risk groups will develop post traumatic stress disorder after birth. Operative deliveries are recognized as a risk factor for PTSD. [14]

Newborn complications

One of the risks of operative vaginal delivery for the newborn, more common with the use of a vacuum, is cephalohematoma, or bruising under the scalp. [5] Extensive bruising may increase the likelihood of clinically significant hyperbilirubinemia. [15] Most of the time increased levels of total serum bilirubin in newborns is a harmless occurrence, however with high enough levels there would be a concern for brain damage. [15]

Infants delivered by vacuum extraction have a higher rate of retinal hemorrhage compared to infants delivered without instrument assistance. [16] It is believed that suction on the head increases intracranial pressure which may cause an increase in arterial blood pressure in the eye leading to retinal bleeding. [16]

Newborns undergoing operative delivery have a higher likelihood of experiencing shoulder dystocia, a delivery emergency that may lead to further injury such as brachial plexus palsy. [17] [18] Scalp and facial injuries leading to fractures and bleeding may be possible. [5]

Epidemiology

Operative vaginal delivery has decreased as second stage caesarean section has become more common, [2] in the United Kingdom 12.7% of women and up to 25% of first time mothers undergo operative vaginal delivery as of 2019. [14] Globally, this percentage decreases to 2.6%. [19] Between 2005 and 2013, 1.1% of vaginal deliveries in the United States were forceps-assisted. [3]

Technique

The procedure relies primarily on either a pair of curved forceps blades or a vacuum extractor that applies negative pressure inside the womb. The forceps are designed to reach the top of the fetal head and create the necessary traction to pull and rotate the baby out. On the other hand, the vacuum extractor uses a small metal or silicon cap that exerts negative pressure on the fetal scalp to facilitate pulling of the infant. [20] Since vacuum extraction can cause less injuries to the mother than forceps-assisted delivery, it is the preferred technique in some countries. [21]

Rotational forceps

Rotational forceps are used to turn the head of the fetus so that it is in the correct position. [22] Rotational forceps, also referred to as Kielland's forceps, were first described by Norwegian obstetrician Christian Kielland in 1908. Their use declined during the twentieth century because they were associated with risks to the mother and baby; however, both the American Congress of Obstetricians and Gynecologists and Royal College of Obstetricians and Gynaecologists (RCOG) from the United Kingdom support the use of rotational forceps by practitioners who have the experience and skill to do so. Neither organization has specific training guidelines, although the RCOG suggests that training should include direct senior supervision and an assessment of skills in the workplace. [9]

An analysis of 4 studies showed that the use of rotational forceps had low rates of postpartum hemorrhage and obstetric anal sphincter injury to the mother. Additionally, neonatal complication rates were similar to those seen with other methods for assisted birth, such as the use of a vacuum cup, manual rotation, or second-stage cesarean section. [9]

An additional analysis of 31 studies found that forceps were more likely to lead to vaginal birth than vacuum cups, but were more likely to have perineal tears to the anus or rectum. There was no difference in postpartum hemorrhage rates for the mother and no difference in Apgar scores to the baby post birth. [5]

Vacuum suction

Vacuum suction can have either rigid or flexible cups, and can be operated with handheld devices or a foot-operated electric pump. Evidence suggests that rigid cups may have higher success rates than soft cups, but may be more likely to cause fetal trauma. [5]

Recovery

Post-delivery care

Injuries such as tears, cuts, or bruises to the birth canal, cervix, anus, or vaginal openings will be assessed and addressed. For example, tears to the vaginal openings will be stitched to prevent blood loss. [23]

Physical exam, hearing and vision tests, imaging will be assessed for the neonate for any signs of trauma. [24] When forceps are used for operative vaginal delivery, the recovery process takes a little longer. When there are injuries such as tears, it takes about six weeks to heal. Stitches used for vaginal openings takes a month to fully absorb before they start disappearing completely. Wearing a postpartum pad is recommended when there is bleeding and to prevent infections. Healthcare providers should be consulted if excess pain occurs so that pain medications can be prescribed or gotten over-the-counter.[ better source needed ] [25]

Antibiotics

Operative vaginal delivery presents an opportunity for infection due to trauma to the tissue, vaginal examination and instrumentation, and bladder catheterization with 0.7–16% of operative vaginal births leading to infections. Guidelines from the World Health Organization (WHO) support the use of intravenous antibiotics for the mother as soon as possible after birth but can be used up to within 6 hours after birth. The recommended antibiotic combination would be amoxicillin and clavulanic acid, but if they are not available antibiotics with similar activity can be used. [26] Due to the use of either forceps or vacuum in operative vaginal deliveries, there has been an increase in maternal infection and in some cases, readmission after delivery due to the infection. The effectiveness of antibiotic prophylaxis was studied in both the use of either forceps or vacuum in operative delivery to reduce the risk of infection. The result showed that antibiotic prophylaxis has been shown to effectively reduce infections in operative vaginal deliveries, and should be used. [27]

History

The concept of forceps for vaginal delivery was invented by Peter Chamberlin in the 1600 which helped became the instrument used in operative vaginal delivery. The use of this instrument for operative vaginal delivery dates back to the 1600's. Throughout history, over 700 types of forceps have been reinvented and gone through modifications to make sure forceps are safe in operative vaginal delivery. [28] Half of first-time mothers had forceps-assisted deliveries in the 1960s. [5]

The vacuum extractor was developed in the mid-1900s, and its use in delivery became more common than forceps in 1992. [5] James Young Simpson in 1849 invented the air tractor used in vacuum extraction to help with operative vaginal delivery. In the early 1950's, Tage Malmstrom developed a modern vacuum extraction that came with modifications for delivery. [29]

Related Research Articles

<span class="mw-page-title-main">Caesarean section</span> Surgical procedure to deliver a baby through an incision in the mothers abdomen

Caesarean section, also known as C-section, cesarean, or caesarean delivery, is the surgical procedure by which one or more babies are delivered through an incision in the mother's abdomen. It is often performed because vaginal delivery would put the mother or child at risk. Reasons for the operation include obstructed labor, twin pregnancy, high blood pressure in the mother, breech birth, shoulder presentation, and problems with the placenta or umbilical cord. A caesarean delivery may be performed based upon the shape of the mother's pelvis or history of a previous C-section. A trial of vaginal birth after C-section may be possible. The World Health Organization recommends that caesarean section be performed only when medically necessary.

<span class="mw-page-title-main">Childbirth</span> Conclusion of the human pregnancy with the expulsion of a fetus from mothers womb

Childbirth, also known as labour, parturition and delivery, is the completion of pregnancy where one or more babies exits the internal environment of the mother via vaginal delivery or caesarean section. In 2019, there were about 140.11 million human births globally. In the developed countries, most deliveries occur in hospitals, while in the developing countries most are home births.

<span class="mw-page-title-main">Episiotomy</span> Surgical incision of the perineum and the posterior vaginal wall

Episiotomy, also known as perineotomy, is a surgical incision of the perineum and the posterior vaginal wall generally done by an obstetrician. This is usually performed during the second stage of labor to quickly enlarge the aperture, allowing the baby to pass through. The incision, which can be done from the posterior midline of the vulva straight toward the anus or at an angle to the right or left, is performed under local anesthetic, and is sutured after delivery.

<span class="mw-page-title-main">Breech birth</span> Birth of a baby bottom first

A breech birth is when a baby is born bottom first instead of head first, as is normal. Around 3–5% of pregnant women at term have a breech baby. Due to their higher than average rate of possible complications for the baby, breech births are generally considered higher risk. Breech births also occur in many other mammals such as dogs and horses, see veterinary obstetrics.

<span class="mw-page-title-main">Vacuum extraction</span> Method to assist the delivery of a baby

Vacuum extraction (VE), also known as ventouse, is a method to assist delivery of a baby using a vacuum device. It is used in the second stage of labor if it has not progressed adequately. It may be an alternative to a forceps delivery and caesarean section. It cannot be used when the baby is in the breech position or for premature births. The use of VE is generally safe, but it can occasionally have negative effects on either the mother or the child. The term ventouse comes from the French word for "suction cup".

A hysterotomy is an incision made in the uterus. This surgical incision is used in several medical procedures, including during termination of pregnancy in the second trimester and delivering the fetus during caesarean section. It is also used to gain access and perform surgery on a fetus during pregnancy to correct birth defects, and it is an option to achieve resuscitation if cardiac arrest occurs during pregnancy and it is necessary to remove the fetus from the uterus.

<span class="mw-page-title-main">Obstructed labour</span> Medical condition

Obstructed labour, also known as labour dystocia, is the baby not exiting the pelvis because it is physically blocked during childbirth although the uterus contracts normally. Complications for the baby include not getting enough oxygen which may result in death. It increases the risk of the mother getting an infection, having uterine rupture, or having post-partum bleeding. Long-term complications for the mother include obstetrical fistula. Obstructed labour is said to result in prolonged labour, when the active phase of labour is longer than 12 hours.

<span class="mw-page-title-main">Shoulder dystocia</span> Birthing obstruction complication

Shoulder dystocia is when, after vaginal delivery of the head, the baby's anterior shoulder gets caught above the mother's pubic bone. Signs include retraction of the baby's head back into the vagina, known as "turtle sign". Complications for the baby may include brachial plexus injury, or clavicle fracture. Complications for the mother may include vaginal or perineal tears, postpartum bleeding, or uterine rupture.

<span class="mw-page-title-main">Prelabor rupture of membranes</span> Breakage of the amniotic sac before the onset of labour

Prelabor rupture of membranes (PROM), previously known as premature rupture of membranes, is breakage of the amniotic sac before the onset of labour. Women usually experience a painless gush or a steady leakage of fluid from the vagina. Complications in the baby may include premature birth, cord compression, and infection. Complications in the mother may include placental abruption and postpartum endometritis.

<span class="mw-page-title-main">Chignon (medical term)</span> Scalp swelling on a newborn due to birth by vacuum extraction

A chignon is a temporary swelling caused by a build-up of bloody fluid left on an infant's head after they have been delivered by vacuum extraction. A vacuum extraction is a type of assistance used during vaginal delivery by an obstetrician or midwife when the second stage of labor, where the cervix is fully dilated allowing for fetus delivery, is stalled. It anatomically resembles regular caput succedaneum, one of two most frequently occurring birth injuries to the head, the other being cephalohematoma, a usually harmless condition where blood accumulates under the newborn's scalp after vaginal delivery.

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.

Caesarean delivery on maternal request (CDMR) is a caesarean section birth requested by the pregnant woman without a medical reason.

In case of a previous caesarean section a subsequent pregnancy can be planned beforehand to be delivered by either of the following two main methods:

<span class="mw-page-title-main">Obstetrical forceps</span> Medical instrument used for the delivery of a baby

Obstetrical forceps are a medical instrument used in childbirth. Their use can serve as an alternative to the ventouse method.

<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, as it is correlated with lower morbidity and mortality than caesarean sections (C-sections), though it is not clear whether this is causal.

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">Perineal tear</span> Medical condition

A perineal tear is a laceration of the skin and other soft tissue structures which, in women, separate the vagina from the anus. Perineal tears mainly occur in women as a result of vaginal childbirth, which strains the perineum. It is the most common form of obstetric injury. Tears vary widely in severity. The majority are superficial and may require no treatment, but severe tears can cause significant bleeding, long-term pain or dysfunction. A perineal tear is distinct from an episiotomy, in which the perineum is intentionally incised to facilitate delivery. Episiotomy, a very rapid birth, or large fetal size can lead to more severe tears which may require surgical intervention.

<span class="mw-page-title-main">Birth trauma (physical)</span> Medical condition

Birth trauma refers to damage of the tissues and organs of a newly delivered child, often as a result of physical pressure or trauma during childbirth. It encompasses the long term consequences, often of cognitive nature, of damage to the brain or cranium. Medical study of birth trauma dates to the 16th century, and the morphological consequences of mishandled delivery are described in Renaissance-era medical literature. Birth injury occupies a unique area of concern and study in the medical canon. In ICD-10 "birth trauma" occupied 49 individual codes (P10–Р15).

Odón device is a medical device that is designed to assist during a difficult birth. The device consists of a plastic sleeve that is inflated around the baby's head and is used to gently pull and ease the head of the infant through the birth canal.

<span class="mw-page-title-main">Prolonged labor</span> Medical condition

Prolonged labor is the inability of a woman to proceed with childbirth upon going into labor. Prolonged labor typically lasts over 20 hours for first time mothers, and over 14 hours for women that have already had children. Failure to progress can take place during two different phases; the latent phase and active phase of labor. The latent phase of labor can be emotionally tiring and cause fatigue, but it typically does not result in further problems. The active phase of labor, on the other hand, if prolonged, can result in long term complications.

References

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  2. 1 2 3 4 "Research gaps and needs to optimize the use of assisted vaginal birth: technical brief". World Health Organization. 2023. Retrieved July 25, 2023.
  3. 1 2 Evanson SM, Riggs J (2023). Forceps Delivery. Treasure Island (FL): StatPearls Publishing. PMID   30855808 . Retrieved 2023-07-31.{{cite book}}: |work= ignored (help)
  4. 1 2 Spinelli A, Laurenti V, Carrano FM, Gonzalez-Díaz E, Borycka-Kiciak K (July 2021). "Diagnosis and Treatment of Obstetric Anal Sphincter Injuries: New Evidence and Perspectives". Journal of Clinical Medicine. 10 (15): 3261. doi: 10.3390/jcm10153261 . PMC   8347477 . PMID   34362045.
  5. 1 2 3 4 5 6 7 8 9 Norwitz ER, Zelop CM, Miller DA, Keefe D, eds. (2019). Evidence-based obstetrics and gynecology. Hoboken: Wiley Blackwell. ISBN   978-1-119-07298-0.
  6. 1 2 Verma, Ganga L.; Spalding, Jessica J.; Wilkinson, Marc D.; Hofmeyr, G. Justus; Vannevel, Valerie; O'Mahony, Fidelma (2021-09-24). "Instruments for assisted vaginal birth". The Cochrane Database of Systematic Reviews. 2021 (9): CD005455. doi:10.1002/14651858.CD005455.pub3. ISSN   1469-493X. PMC   8462579 . PMID   34559884.
  7. ↑ Nassr AA, Hessami K, Berghella V, Bibbo C, Shamshirsaz AA, Shirdel Abdolmaleki A, et al. (September 2022). "Angle of progression measured using transperineal ultrasound for prediction of uncomplicated operative vaginal delivery: systematic review and meta-analysis". Ultrasound in Obstetrics & Gynecology. 60 (3): 338–345. doi:10.1002/uog.24886. PMID   35238424. S2CID   247221617.
  8. ↑ "Operative Vaginal Delivery – Gynecology and Obstetrics". Merck Manuals Professional Edition. Retrieved 2023-07-31.
  9. 1 2 3 4 Nash Z, Nathan B, Mascarenhas L (January 2015). "Kielland's forceps. From controversy to consensus?". Acta Obstetricia et Gynecologica Scandinavica. 94 (1): 8–12. doi: 10.1111/aogs.12511 . PMID   25233861. S2CID   1202262.
  10. ↑ Jeon J, Na S (November 2017). "Vacuum extraction vaginal delivery: current trend and safety". Obstetrics & Gynecology Science. 60 (6): 499–505. doi:10.5468/ogs.2017.60.6.499. PMC   5694723 . PMID   29184857.
  11. ↑ Vannevel V, Swanepoel C, Pattinson RC (April 2019). "Global perspectives on operative vaginal deliveries". Best Practice & Research. Clinical Obstetrics & Gynaecology. Operative Vaginal Delivery. 56: 107–113. doi:10.1016/j.bpobgyn.2018.09.004. hdl: 2263/67362 . PMID   30392949. S2CID   53217596.
  12. ↑ Deane RP (April 2019). "Operative vaginal delivery and pelvic floor complications". Best Practice & Research. Clinical Obstetrics & Gynaecology. 56: 81–92. doi:10.1016/j.bpobgyn.2019.01.013. PMID   30850327. S2CID   73494593.
  13. ↑ Okeahialam NA, Wong KW, Jha S, Sultan AH, Thakar R (June 2022). "Mediolateral/lateral episiotomy with operative vaginal delivery and the risk reduction of obstetric anal sphincter injury (OASI): A systematic review and meta-analysis". International Urogynecology Journal. 33 (6): 1393–1405. doi:10.1007/s00192-022-05145-1. PMC   9206628 . PMID   35426490.
  14. 1 2 Kirk L, Bahl R (April 2019). "Nontechnical skills and decision making in operative vaginal delivery". Best Practice & Research. Clinical Obstetrics & Gynaecology. 56: 23–34. doi:10.1016/j.bpobgyn.2019.02.001. PMID   30826158. S2CID   73501474.
  15. 1 2 Watchko JF (June 2009). "Identification of neonates at risk for hazardous hyperbilirubinemia: emerging clinical insights". Pediatric Clinics of North America. Advances in Neonatology. 56 (3): 671–87, Table of Contents. doi:10.1016/j.pcl.2009.04.005. PMID   19501698.
  16. 1 2 Watts P, Maguire S, Kwok T, Talabani B, Mann M, Wiener J, et al. (February 2013). "Newborn retinal hemorrhages: a systematic review". Journal of AAPOS. 17 (1): 70–78. doi: 10.1016/j.jaapos.2012.07.012 . PMID   23363882.
  17. ↑ Mehta SH, Sokol RJ (June 2014). "Shoulder dystocia: risk factors, predictability, and preventability". Seminars in Perinatology. Shoulder dystocia and neonatal brachial plexus palsy. 38 (4): 189–193. doi:10.1053/j.semperi.2014.04.003. PMID   24863023.
  18. ↑ Zafeiriou DI, Psychogiou K (April 2008). "Obstetrical brachial plexus palsy". Pediatric Neurology. 38 (4): 235–242. doi:10.1016/j.pediatrneurol.2007.09.013. PMID   18358400.
  19. ↑ Thierens S, van Binsbergen A, Nolens B, van den Akker T, Bloemenkamp K, Rijken MJ (May 2023). "Vacuum extraction or caesarean section in the second stage of labour: A systematic review". BJOG. 130 (6): 586–598. doi: 10.1111/1471-0528.17394 . hdl: 1887/3728595 . PMID   36660890. S2CID   256031479.
  20. ↑ Chamberlain G, Steer P (May 1999). "ABC of labour care: operative delivery". BMJ. 318 (7193): 1260–1264. doi:10.1136/bmj.318.7193.1260. PMC   1115650 . PMID   10231260.
  21. ↑ Thierens S, van Binsbergen A, Nolens B, van den Akker T, Bloemenkamp K, Rijken MJ (May 2023). "Vacuum extraction or caesarean section in the second stage of labour: A systematic review". BJOG. 130 (6): 586–598. doi: 10.1111/1471-0528.17394 . hdl: 1887/3728595 . PMID   36660890. S2CID   256031479.
  22. ↑ Verma GL, Spalding JJ, Wilkinson MD, Hofmeyr GJ, Vannevel V, O'Mahony F (September 2021). "Instruments for assisted vaginal birth". The Cochrane Database of Systematic Reviews. 2021 (9): CD005455. doi:10.1002/14651858.CD005455.pub3. PMC   8462579 . PMID   34559884.
  23. ↑ Belfort MA (2023). Operative Techniques in Obstetric Surgery (1st ed.). Philadelphia, Pennsylvania: Wolters Kluwer Health. pp. 223–249. ISBN   9781975136734.
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  25. ↑ "Forceps Delivery". Cleveland Clinic.
  26. ↑ "WHO recommendation on Routine antibiotic prophylaxis for women undergoing operative vaginal birth". Geneva: World Health Organization. 2021. Retrieved July 25, 2023.
  27. ↑ Liabsuetrakul T, Choobun T, Peeyananjarassri K, Islam QM (March 2020). "Antibiotic prophylaxis for operative vaginal delivery". The Cochrane Database of Systematic Reviews. 2020 (3): CD004455. doi:10.1002/14651858.CD004455.pub5. PMC   7096725 . PMID   32215906.
  28. ↑ Goetzinger KR, Macones GA (May 2008). "Operative vaginal delivery: current trends in obstetrics". Women's Health. 4 (3): 281–290. doi: 10.2217/17455057.4.3.281 . PMID   19072477. S2CID   19643710.
  29. ↑ "Vacuum Extraction: Introduction and History, Prerequisites for Vacuum Extraction, Indications for Vacuum Extraction". 2019-11-09.
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