Table of Content
- What is a placenta?
- What does the placenta do?
- Placental health
- Twin-to-twin transfusion syndrome
- Placental complications
- Placenta praevia
- Placenta abruptio
- Placenta accreta
- Retained placenta
- Third stage of labour: delivery of the placenta
- Delayed cord clamping
- What happens to the placenta after delivery?
- Lotus birth
What is a placenta?
The placenta (from the Greek word ‘plakuos’ meaning flat cake) is an organ that supports foetal life during pregnancy. The placenta attaches to the lining of the womb during pregnancy and begins developing from Day 8  after the blastocyst locates a suitable implantation site in the uterine wall. Around Day 21 of pregnancy, the placenta begins to function and will continue to grow alongside the developing foetus until, at term, the placenta is about 20cm in diameter, 3cm thick and weighs between 500-600g.  There are two sides to a human placenta:
- The foetal side – this side faces the foetus in utero, is smooth and shiny and is the connection site of the umbilical cord.
- The mother’s side – this side implants in the uterine wall, and is rough and wrinkled. 
All placental mammals develop placentas during pregnancy to sustain the growing foetus but placentas vary from species to species – human placentas are discoid and hemochorial (disc-shaped) and one where the maternal blood comes into direct contact with the outer membrane covering the foetus. 
The umbilical cord (also known as ‘funiculus umbilicalis’) is a flexible cord that is 50-60cm in length and 1.5cm in diameter and connects the foetus to the placenta.  The umbilical cord contains two arteries and one vein which are protected by a sticky substance called Wharton’s jelly. The umbilical vein delivers oxygen and nutrient-rich blood to the foetus, while the umbilical arteries return depleted blood back to the maternal bloodstream. 
What does the placenta do?
The placenta supports the growth and development of the foetus in utero, and uses the umbilical cord to manage nutrition, waste removal and gas exchange, as well as providing support for the immune and endocrine systems. 
Nutrition, waste and gas exchange – Oxygen and nutrient-rich blood is carried to the foetus from the placenta through the umbilical cord. The foetal heart pumps the deoxygenated blood back through the umbilical cord to the placenta into the maternal bloodstream. Foetal waste products such as uric acid are released into the amniotic fluid and then diffuse across the placenta and are then excreted via the maternal kidneys. 
Endocrine system – During pregnancy, the placenta secretes hormones including:
- Human Chorionic Gonadotropin (hCG) – this is the first placental hormone and is the hormone that is tested for in urine and blood pregnancy tests. This hormone is only present during pregnancy because it is secreted by the placenta.
- Human Placental Lactogen (hPL) – this hormone promotes mammary gland growth and prepares the maternal body for lactation.
- Oestrogen – this is a steroid hormone and stimulates the growth of the uterus and allows it to contract, which prepares it for labour.
- Progesterone – this is a steroid hormone and maintains the endometrial lining of the uterus and prevents premature labour. 
Immune system – The placenta offers some protection to the foetus against bacterial infection. However, it cannot provide any protection against viruses, which can cross the placenta. The rubella virus (also known as German measles) can cause miscarriage, stillbirth or birth defects such as deafness and heart, lung and brain abnormalities.  In the last weeks of pregnancy, maternal antibodies are passed to the foetus and will give the newborn baby passive immunity for about three months after birth. 
Various factors can impact on the health of the placenta and its ability to perform correctly. These include:
- Maternal age – older mothers are at higher risk of placental abruption. 
- High blood pressure – Can cause a raft of pregnancy complications including a decreased blood flow through the placenta, which can slow the foetus’ growth and result in low birth weight. 
- Previous uterine surgery – Women who have had previous caesarean sections are at higher risk of placental complications such as placenta praevia and placenta accreta. 
- Diabetes – This can cause placental insufficiency, where the placenta does not work as well as it should and can cause the foetus’ growth to slow as a result. 
- Multiple pregnancy – Dichorionic twins (each twin having its own placenta) are at increased risk of placenta praevia, while monochorionic twins (twins sharing one placenta) are at increased risk of placenta abrupto. 
- Substance abuse – smoking cigarettes and drug use, particularly cocaine, marijuana and alcohol use, can result in placental insufficiency. 
- Previous placental problems – If you’ve had a placental problem in a previous pregnancy, you are at higher risk of experiencing one again. 
Signs of placental problems
Symptoms such as the following can signify that there are problems with the placenta:
- Abdominal pain
- Severe back pain
- Vaginal bleeding
- Rapid uterine contractions 
Any of these symptoms should be checked by a health care professional immediately.
A small amount of vaginal bleeding during labour is normal (an amount less than a normal period). This can be pink, bright red or dark brown in colour sometimes mixed with mucus as a show, sometimes mixed with amniotic fluid as the waters break. Slight bleeding can be something noticed on a sanitary pad, or staining underwear or when wiping with toilet paper. However, a few women don’t experience any vaginal bleeding at all during their labour, only at the birth. A small amount of blood can come away during prelabour, and/or the first and second stages of labour (continuously or intermittently), as the cervix dilates and the baby negotiates the birth canal. It can also start (or become slightly heavier) after an internal vaginal examination. Significant bleeding (soaking a pad or more) during labour is of concern, and is referred to as an Intrapartum Haemorrhage (IPH). Very heavy bleeding after the baby is born is referred to as a postpartum haemorrhage (PPH) .
The main causes of an intrapartum haemorrhage are placenta previa (low lying placenta), placental abruption (the placenta separating too early from the wall of the uterus) or unusual placenta formations such as vasa previa and velamentous insertion .
Twin-to-twin transfusion syndrome
Up to 60-70 percent of identical twins share the same placenta, but separate amniotic sacs.  Twin-to-twin tranfusion syndrome (TTTS) is a serious condition that only occurs in identical (monozygotic) twins who share a placenta, which can be life-threatening to both foetuses if left untreated.
Twin-to-twin transfusion syndrome occurs when the single placenta is shared unequally between the two foetuses, with the result that blood is transfused disproportionately from the ‘donor’ twin to the ‘recipient’ twin.
This disproportionate transfusion results in the donor twin having less blood volume than its twin, which in turn results in the donor twin growing more slowly than its twin. It also results in less urine output for the donor twin which means less amniotic fluid.
For the recipient twin, more blood volume can cause greater pressure on the heart and can result in heart failure; greater blood volume also means greater urine output and more amniotic fluid, which can cause complications such as placenta abrupto, cord prolapse and miscarriage. 
A normal healthy placenta develops in the first days of pregnancy and grows along the lining of the uterus, usually in the upper part, and is attached to the foetus by the umbilical cord. The placenta continues to grow as the foetus grows until it is delivered in the third stage of labour shortly after the birth of the baby.
Most women won’t experience any problems with their placenta during pregnancy, but there are a number placental complications that can occur, including:
Placenta praevia occurs in approximately 1 in 200 to 250 pregnancies  and is a complication that occurs when the placenta lies low in the uterus and either partially or totally covers the cervix, which can cause bleeding before or during birth. Placenta praevia is the leading cause of post-partum haemorrhage  and as a consequence, caesarean section is usually the recommended delivery method as it poses less risk to mother and baby.
Painless bleeding during the second trimester is a symptom of placenta praevia, and the condition can be confirmed through an ultrasound. Once placenta praevia has been identified, bed rest is usually recommended as a precaution. Approximately 50 percent of all cases result in premature labour. 
Ultrasounds are not 100 per cent accurate and it may question the presence of a low-lying placenta, even though it is situated normally. Also, it might not be able to pick up that the placenta is low lying. Ultrasounds done through your belly are generally regarded as less accurate at diagnosing placenta praevia, because the cervix is situated very low down in the woman’s pelvis. Ultrasounds done with a probe into the woman’s vagina are suggested as being more accurate, but are not generally recommended if placenta praevia is suspected, as any vaginal examination could stimulate bleeding .
A low-lying placenta may affect the level of oxygen and nutrients the baby receives. This is because the lower segment of the uterus (where the placenta is implanted) is thinner muscle, usually only designed to absorb the cervix during labour. The lower segment has less blood supply than the upper segment, and therefore may not nourish the baby as efficiently. It is more difficult for the placenta to implant properly into the lower segment, and also more likely parts of the placenta will separate from the wall of the uterus during bleeding (meaning less placental tissue being able to function efficiently) .
If placenta praevia is picked up during pregnancy, then you can expect the following care and treatment :
- Bed rest - Your caregiver may suggest stopping work and resting at home if the bleeding is light and the grade of placenta praevia is not severe. If the placenta previa is major and/or the bleeding has been heavy, admission to hospital may be required. Ideally the hospital would have obstetric doctors onsite and facilities to perform an emergency Caesarean operation if this was required relatively quickly. Some research studies question the need for admission to hospital in cases where the woman has not bled yet, or the bleeding has been minimal. The general recommendation is that these women be allowed to stay at home.
- An intravenous (IV) cannula - If admitted to hospital, you may have an intravenous (IV) cannula placed in your arm. This is in case fluids need to be given through the vein with a drip if the bleeding becomes heavy. A cannula is a small, plastic tube inserted with a needle into the vein, with the tube left in place and the needle being removed. The cannula is taped securely with about one to two centimetres of the capped end sitting out of the skin. Cannulas are normally covered with a plastic dressing, so you can use the bath or shower. Sterile salt water is injected by the caregiver through the cannula every four to six hours, to keep the cannula clear of blood clots, so it remains usable in an emergency. If the woman experiences a heavy bleed, she may be given fluids through her vein, in severe case, a blood transfusion may be required. The cannula can also be used if an emergency caesarean operation is needed. Some women have been known to donate their own blood early in the pregnancy in case they require a blood transfusion (called an autologous transfusion). However, this would not be recommended if you were anaemic (having a low haemoglobin).
- Regular monitoring of the baby’s health - After vaginal bleeding, your caregiver will usually want to regularly monitor your baby’s health using ultrasounds and CTG monitoring. These may be used on a regular (weekly or fortnightly) basis or just when bleeding occurs. Ultrasounds may be done more regularly if there are concerns about the ongoing growth of the baby.
- Ultrasound - Besides monitoring the baby’s health, an ultrasound may also be used before a scheduled Caesarean operation to help the doctor know exactly where the placenta is lying so they may avoid cutting into the placenta during the operation and risking excessive blood loss. However, sometimes the placenta is positioned in a way that makes this unavoidable.
- Elective caesarean - Some caregivers recommend an elective caesarean at about 38 to 40 weeks of pregnancy, or earlier if the bleeding has been heavy and/or a vaginal birth is thought to be impossible. There is debate about the most appropriate anaesthetic that can be used in these circumstances. An epidural anaesthetic may contribute to lowering the woman’s blood pressure, and since heavy bleeding also reduces blood pressure, the combined effects can increase this risk to the woman. On the other hand a general anaesthetic also holds increased risks for the mother and baby, so the pros and cons need to be weighed up with the anaesthetist.
- Induction of labour - If the placenta is low-lying, but not covering the woman’s cervix, the caregiver may suggest an induction of labour at 38 to 40 weeks. The baby would be monitored with a CTG machine during the labour in the delivery suite, and if there is very heavy bleeding before the birth, a Caesarean operation would be performed.
- Internal vaginal examination in the operating theatre - Some caregivers recommend they attempt to feel just how far away the edge of the placenta is from the cervix. To do this, the doctor places one finger inside the cervix, and gently feels up inside the uterus, until they can feel the edge of the placenta (or hopefully not be able to reach it). If the placenta is felt to be about five centimetres away or more, a vaginal birth may be regarded as possible. The cervix usually needs to open five centimetres each way, to get to 10 centimetres dilation. Internal examinations hold the risk of stimulating a heavy bleed and if the bleeding is severe enough, an emergency caesarean may be required. This is why the procedure is usually carried out in the operating theatre, so it can be performed straight away. There is a debate about the use of a general anaesthetic (GA) during this procedure. Doing the examination without one can be quite uncomfortable, but using a general anaesthetic holds health risks for the woman and her baby.
- Injection of anti-D immunoglobulin - Bleeding from the placenta can sometimes cause a small amount of the baby’s blood to pass into the woman’s blood stream. If the woman’s blood group is Rhesus (Rh) negative (eg. O Negative) and the baby’s blood is Rhesus (Rh) positive, this can cause an antibody reaction in the woman’s body. This is not a problem for the current pregnancy, but can cause problems for future pregnancies. An injection of Anti-D immunoglobulin is usually given to women with a negative Rhesus factor after a heavy bleed, aimed at preventing this reaction. Anti-D immunoglobulin can be effective for up to three months, but may need to be repeated after a heavy bleed if not given for a while, and given again after the birth of the baby.
Occasionally, you may not be aware that you have placenta praevia before the labour, especially if the baby is premature, have not experienced any bleeding late in the pregnancy. In this case, your caregiver will suspect it if you start to bleed more heavily than normal during labour .
There are four different medically categorised varieties of placenta praevia, unique in their severity :
- Grade 1 or minor is when part of the placenta is implanted in the lower segment of the uterus, but the edge is more than five centimetres (two inches) away from the woman’s cervix. Most of the placenta is situated normally, in the upper segment of the uterus. The cervix needs to dilate 10 centimetres in labour, usually five centimetres each way, for the woman to give birth vaginally.
- Grade 2 also minor is when most of the placenta is implanted in the lower segment, and the edge of the placenta touches the edge of the cervical opening, but does not cover it.
- Grade 3 or major is when the placenta is implanted in the lower segment and part of the placenta covers some of the cervical opening.
- Grade 4 also major is when the placenta totally covers the woman’s cervix.There is another type of placenta praevia, where most of the placental tissue is situated in the upper segment, but there is a small piece of placenta that implants away from the main body of the placenta, over or near the cervix. This is a satellite lobe or succenturiate lobe and is connected to the main placenta by a large blood vessel running through the sac or membrane . This is rare and may be difficult to detect on ultrasound .
More severe cases of placenta praevia are prone to bleed heavily during labour, and if the placenta fully covers the cervix, will prevent the baby from being able to be born. After birth, baby may need to go to the intensive care nursery. This will depend on how distressed the baby is, and if the baby lost any blood or needed extensive resuscitation at birth .
Placenta accreta is a very rare complication of placenta previa. It can happen when the placenta is adhered (and will not separate) from the wall of the woman’s uterus. This is because the placenta has implanted in the actual muscle of the uterus, rather than into the lining of the uterus, (which is typically sparse in the lower segment). If the placenta is unable to be removed manually by the caregiver’s hand (after a vaginal birth, or during a Caesarean operation), the doctor will try to cut the placenta away in the operating theatre. They may choose to leave the placenta in the uterus in the hope it will be naturally reabsorbed (which has varying degrees of success). In rare circumstances, a hysterectomy may be required .
Placenta abruptio (also known as a placenta abruption or accidental haemorrhage) is a rare complication (about 0.5 percent of pregnancies) that happens when the placenta lifts off the wall of the uterus, usually in the middle of the placenta. This allows blood to pool and clot behind the placenta between the placenta, and the wall of the uterus (called a ‘retroplacental clot’). This detachment can be either partial or total and can result in haemorrhage in the mother and loss of oxygen to the baby .
Placenta abruptio occurs in approximately one in 150 deliveries.  Once detached, the placenta cannot be reattached. Partial detachments are monitored closely and managed through bed rest. A caesarean delivery is often recommended to manage excessive blood loss.
The signs of a placental abruption in labour usually include :
- the contractions stopping abruptly
- the baby’s heart rate dropping abnormally low
- severe, constant abdominal pain or back pain that may be associated with some vaginal bleeding.
A placental abruption can be associated with health conditions such as ::
- Very high blood pressure. Pre-eclampsia and eclampsia are the most common causes of a placental abruption.
- An injury or severe blow to the woman’s stomach. This could occur in a motor vehicle accident, being kicked in the stomach or after a heavy fall.
- The woman smoking or her diet being unhealthy.
- A rare complication due to an external cephalic version (ECV). This is when the caregiver turns a baby from a breech position, to a head down position. Or as a rare complication from an amnioreduction. A procedure where the caregiver removes excess amniotic fluid from around the baby because of polyhydramnios.
- Sometimes for no known reason.
Because much of the blood accumulates behind the placenta, the amount of blood that can be noticed coming away from the vagina may not be that much. If you, or your caregivers, feel the uterus, it is often very tender, or painful to touch .
Sometimes small clots can be observed on ultrasound, but they do not significantly affect the health of the woman, or the baby. The pregnancy can still progress normally, and there are no complications. If the clot is very large and/or the bleeding continues, the woman and baby are at risk and an emergency caesarean is often the only alternative .
In most cases, the cause of placenta abruptio is unknown but abdominal trauma and uterine decompression are two known causes. 
This placental complication occurs when the placenta attaches itself too deeply into the uterine wall, and in some cases grows completely through the endometrium. Placenta accreta is also known as Placenta increta and Placenta percreta – with each name signifying a level of penetration into the uterine wall:
- Placenta accreta– Occurring in approximately 75 percent of all cases, the placenta attaches to the myometrium (uterine muscles) but does not penetrate them.
- Placenta increta – Occurring in approximately 15 percent of all cases, the placenta attaches and penetrates the myometrium.
- Placenta percreta – Occurring in approximately 5 percent of all cases, the placenta penetrates the myometrium and beyond, through the uterine wall. In some cases, placenta percreta can invade other organs such as the bladder. 
Cases of placenta accreta are increasing, with risk factors including previous uterine scar tissue including caesarean scars and previous placenta praevia. 
Placenta accreta is extremely difficult to diagnose before birth and is usually discovered when the third stage of labour – delivery of the placenta – fails to progress. The common treatment for this condition is surgical removal of the placenta to avoid excessive blood loss.
A retained placenta occurs when the third stage of labour – the delivery of the placenta – fails to progress. The placenta is regarded as retained if:
- The placenta partially separates – Heavy and uncontrolled bleeding can occur when the placenta only partially separates from the uterine wall because the uterus cannot contract due to the placenta still being partially attached.
- The placenta remains wholly attached – There is no bleeding attached to this condition but after a prolonged amount of time, if no interventions result in the delivery of the placenta, manual extraction will be undertaken to remove the placenta.
- The cervix closes before the placenta is delivered – The placenta detaches from the uterine wall but cannot be delivered due to the cervix closing prematurely. This can lead to post-partum haemorrhage. 
Third stage of labour: delivery of the placenta
After delivery of the baby, the final stage of labour – the third stage – is the delivery of the placenta. This phase of labour usually lasts no more than 30 minutes and is completed when the placenta is entirely expelled from the uterus.
The delivery of the placenta is managed either by two methods:
- Following the birth of the baby, the mother receives an injection of oxytocin in the thigh, which helps the uterus to contract.
- The umbilical cord is clamped.
- The midwife checks for signs of placental separation – often a small amount of blood becomes evident.
- The midwife applies pressure on the pelvic bone and gently pulls on the cord to deliver the placenta.
- The third stage takes 5-10 minutes to complete.
- The umbilical cord is left unclamped.
- Contractions will continue to be experienced.
- A small trickle of blood will be evidence of the placenta separating from the uterine wall.
- The contractions may intensify until there is an urge to push – at which point the placenta will be delivered.
- Once the placenta is delivered the cord is clamped and cut.
- This process can take 10-60 minutes. 
Delayed cord clamping
The practice of delayed cord clamping occurs when the umbilical cord is not immediately clamped after the birth of a baby. Delayed cord clamping is defined as the cord being clamped two to three minutes after birth. 
Medical experts continue to debate the pros and cons of immediate clamping versus delayed clamping, with ongoing discussion about the optimal time to clamp the cord. 
Benefits of immediate cord clamping
- May prevent severe post-partum haemorrhaging.
- Collection of cord blood for storing can take place.
- No delay in resuscitation of the baby if needed.
Benefits of delayed cord clamping
- One-third of a baby’s blood volume is in the placenta – a three minute delayed cord clamping allows 90 percent of this blood to transfuse back to the baby
- Premature babies benefit from the delivery of extra blood volume and are then at lower risk of intraventricular haemorrhage (bleeding in the brain) 
- A rich supply of stem cells is delivered to the newborn baby
What happens to the placenta after delivery?
In hospital deliveries, the placenta is considered to be biohazard waste after it has been delivered and is standardly disposed of with other hospital biohazard waste. The most common method of disposal is incineration.
In home births, new parents are free to dispose of their placenta as they wish. They are supplied with a medical waste disposal bag to correctly dispose of the placenta if they don’t wish to keep it. 
Many hospitals now allow new parents to take the placenta home with them according to specific health guidelines. 
Lotus birth describes the practice of non-severance of the umbilical cord after the delivery of baby and placenta, so that the newborn baby remains attached to the placenta until the cord naturally separates at the umbilicus.
The process of separation takes between three and 10 days – the same amount of time a clamped cord would take to separate.
The benefits of lotus birthing are the same as those of delayed cord clamping – the newborn receives the maximum blood volume transfused from the placenta as well as their own stem cells.
Proponents of lotus birthing also believe that this approach provides a gentle transition for the baby into the family unit. Lotus birthing ensures that mother and baby spend the first days post-partum resting and lying in. 
Arguments that lotus birthing also reduces the risk of infection at the umbilical site because of the lack of wound have been countered by experts who argue that infection risks actually increase with lotus births. The Royal College of Obstetricians and Gynaecologists have said, “If left for a period of time after the birth, there is a risk of infection in the placenta which can consequently spread to the baby. The placenta is particularly prone to infection as it contains blood. Within a short time after birth, once the umbilical cord has stopped pulsating, the placenta has no circulation and is essentially dead tissue.” 
Additionally, some experts question the value of non-severance of the cord, given that all the benefits of delayed cord clamping are delivered to the baby in the first three minutes after delivery. 
More useful references
- Placenta development; UNSW Embryology
- Placental formation; Penn Medicine, Medical Animation Library
- Placenta praevia; Vic Govt, The Better Health Channel
- Delivery of the placenta: Should I have active or natural management? WA Govt, Dept of Health
- Common objections to delayed cord clamping: what does the evidence say? Science & Sensibility
More information on placentas from Kidspot and Birth
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