A stillbirth occurs when a fetus has died in the uterus. A wide variety of definitions exist. The Australian definition specifies that fetal death is termed a stillbirth after 20 weeks gestation or the fetus weighs more than 400 grams (14 oz). Once the fetus has died, the mother may or may not have contractions and undergo childbirth. The term is often used in distinction to live birth or miscarriage. Most stillbirths occur in full-term pregnancies.
The causes of a large percentage of human stillbirths remain unknown, even in cases where extensive testing and autopsy have been performed. A rarely used term to describe these is sudden antenatal death syndrome or SADS, a phrase coined by Cacciatore & Collins in 2000.
In cases where the cause is known, some possibilities of the cause of death are:
* bacterial infection
* birth defects, especially pulmonary hypoplasia
* chromosomal aberrations
* growth retardation
* intrahepatic cholestasis of pregnancy
* maternal diabetes
* high blood pressure, including preeclampsia
* maternal consumption of recreational drugs (such as alcohol, nicotine, etc.) or pharmaceutical drugs contraindicated in pregnancy
* postdate pregnancy
* placental abruptions
* physical trauma
* radiation poisoning
* Rh disease
* umbilical cord accidents
o "Prolapsed umbilical cord" - Prolapse of the umbilical cord happens when the fetus is not in a correct position in the pelvis. Membranes rupture and the cord is pushed out through the cervix. When the fetus pushes on the cervix, the cord is compressed and blocks blood and oxygen flow to the fetus. The mother has approximately 10 minutes to get to a doctor before there is any harm done to the fetus.
o "Monoamniotic twins" - These twins share the same placenta and the same amniotic sac and therefore can interfere with each other's umbilical cords. When entanglement of the cords is detected, it is highly recommended to deliver the fetuses as early as 31 weeks.
Entanglement of cord in twin pregnancy at the time of Caesarean Section
o Umbilical cord length - A short umbilical cord (<30 cm) can affect the fetus in that fetal movements can cause cord compression, constriction and ruptures. A long umbilical cord (>72 cm) can affect the fetus depending on the way the fetus interacts with the cord. Some fetuses grasp the umbilical cord but it is yet unknown as to whether a fetus is strong enough to compress and stop blood flow through the cord. Also, an active fetus, one that frequently repositions itself in the uterus can cause entanglement with the cord.a hyperactive fetus should be evaluated with ultrasound to rule out cord entanglement.
o Cord entanglement - The umbilical cord can wrap around an extremity, the body or the neck of the fetus. When the cord is wrapped around the neck of the fetus it is called a nuchal cord. Again, these entanglements can cause constriction of blood flow. These entanglements can be visualized with ultrasound.
o Torsion - This term refers to the twisting of the umbilical around itself. Torsion of the umbilical cord is very common ( especially in equine stillbirths) but it is not a natural state of the umbilical cord.The umbilical cord can be untwisted at delivery. The average cord has 3 twists.
Sometimes a pregnancy is terminated deliberately during a late phase, for example for congenital anomaly. UK law requires these procedures to be registered as "stillbirths".
It is unknown how much time is needed for a fetus to die. Fetal behavior is consistent and a change in the fetus' movements or sleep-wake cycles can indicate fetal distress. A decrease or cessation in sensations of fetal activity may be an indication of fetal distress or death, though it is not entirely uncommon for a healthy fetus to exhibit such changes, particularly near the end of a pregnancy when there is considerably little space in the uterus for the fetus to move about. Still, medical examination, including a nonstress test, is recommended in the event of any type of any change in the strength or frequency of fetal movement, especially a complete cease; most midwives and obstetricians recommend the use of a kick chart to assist in detecting any changes. Fetal distress or death can be confirmed or ruled out via fetoscopy/doptone, ultrasound, and/or electronic fetal monitoring. If the fetus is alive but inactive, extra attention will be given to the placenta and umbilical cord during ultrasound examination to ensure that there is no compromise of oxygen and nutrient delivery.
Constricted umbilical cord
When the umbilical cord is constricted (q.v. "accidents" above), the fetus experiences periods of hypoxia, and may respond by unusually high periods of kicking or struggling, to free the umbilical cord. These are sporadic if constriction is due to a change in the fetus' or mother's position, and may become worse or more frequent as the fetus grows. Extra attention should be given if mothers experience large increases in kicking from previous childbirths, especially when increases correspond to position changes.
As many of the causes are unknown or untreatable, prevention is difficult. Symptoms of bacterial infection, such as from a dental abscess, in pregnant women may also include unusual periods of incoherence and symptoms of shock, and should be treated by a physician immediately. High blood pressure, diabetes and drug use should be regulated with physician's advice. Umbilical cord constriction may be identified and observed by ultrasound.
Research published in the Journal of the American Medical Association in 2011 found a number of maternal factors associated with stillbirth. Among them: being age 40 or older, having diabetes, having a history of addiction to illegal drugs, being overweight or obese, and smoking cigarettes in the three months before getting pregnant. 
Prenatal maternal treatment
An in utero stillbirth does not usually present an immediate health risk to the woman and labour will usually begin spontaneously after two weeks, so the woman may choose to wait and birth the fetal remains vaginally. After two weeks, the woman is at risk of developing blood clotting problems, and labor induction is recommended at this point. In many cases, the woman will find the idea of carrying the dead fetus emotionally traumatizing and will elect to be induced. Caesarean birth is not recommended unless complications develop during vaginal birth.
Stillbirth is a relatively common, but often random, occurrence. The mean stillbirth rate in the United States is approximately 1 in 115 births, which is roughly 26,000 stillbirths each year, or on an average one every 20 minutes. In Australia, England, Wales, and Northern Ireland, the rate is approximately 1 in every 200 births, in Scotland 1 in 167. (From The National Statistical Office and other sources.) Many stillbirths occur at fullterm to apparently healthy mothers, and a postmortem evaluation reveals a cause of death in only about 40% of autopsied cases.
In developing countries, where medical care can be of low quality or unavailable, the stillbirth rate is much higher.
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