TRAP sequence can be diagnosed using obstetric ultrasound. Doppler interrogation will confirm that blood flow in the acardiac twin is in the reverse direction, entering via the umbilical cord artery and exiting through the vein.

If left untreated, the pump twin will die in 50–75% of cases.

After diagnosis, ultrasound and amniocentesis are used to rule out genetic abnormalities in the pump twin. A procedure may then be performed which will stop the abnormal blood flow. The acardiac twin may be selectively removed. The umbilical cord of the acardiac twin may be surgically cut, separating it from the pump twin, a procedure called fetoscopic cord occlusion. Or a radio-frequency ablation needle may be used to coagulate the blood in the acardiac twin's umbilical cord. This last procedure is the least invasive. These procedures greatly increase the survival chances of the pump twin, to about 80%.

The pump twin will be monitored for signs of heart failure with echocardiograms. If the pump twin's condition deteriorates, the obstetrician may recommend early delivery. Otherwise, the pregnancy continues normally. Vaginal birth is possible unless the fetus is in distress, although it is recommended that the delivery take place at a hospital with NICU capabilities.

This is equivalent of zero intervention. It has been associated with almost 100% mortality rate of one or all fetuses. Exceptions to this include patients that are still in Stage 1 TTTS and are past 22 weeks gestation.

A staging system proposed by fetal surgeon Dr. Ruben Quintero is commonly used to classify the severity of TTTS.

Stage I: A small amount of amniotic fluid (oligohydramnios) is found around the donor twin and a large amount of amniotic fluid (polyhydramnios) is found around the recipient twin.

Stage II: In addition to the description above, the ultrasound is not able to identify the bladder in the donor twin.

Stage III: In addition to the characteristics of Stages I and II, there is abnormal blood flow in the umbilical cords of the twins.

Stage IV: In addition to all of the above findings, the recipient twin has swelling under the skin and appears to be experiencing heart failure (fetal hydrops).

Stage V: In addition to all of the above findings, one of the twins has died. This can happen to either twin. The risk to either the donor or the recipient is roughly equal & is quite high in Stage II or higher TTTS.

The Quintero staging does not provide information about prognosis, and other staging systems have been proposed.

Hydrops fetalis can be diagnosed and monitored by ultrasound scans. Prenatal ultrasound scanning enables early recognition of hydrops fetalis and has been enhanced with the introduction of MCA Doppler.

When a baby is born bottom first there is more risk that the birth will not be straight forward and that the baby could be harmed. For example, when the baby's head passes through the mother’s pelvis the umbilical cord can be compressed which prevents delivery of oxygenated blood to the baby. Due to this and other risks, babies in breech position are usually born by a planned caesarean section in developed countries.

Caesarean section reduces the risk of harm or death for the baby but does increase risk of harm to the mother compared with a vaginal delivery. It is best if the baby is in a head down position so that they can be born vaginally with less risk of harm to both mother and baby. The next section is looking at External cephalic version or ECV which is a method that can help the baby turn from a breech position to a head down position.

Vaginal birth of a breech baby has its risks but caesarean sections are not always available or possible, a mother might arrive in hospital at a late stage of her labour or may choose not to have a caesarean section. In these cases, it is important that the clinical skills needed to deliver breech babies are not lost so that mothers and babies are as safe as possible. Compared with developed countries, planned caesarean sections have not produced as good results in developing countries - it is suggested that this is due to more breech vaginal deliveries being performed by experienced, skilled practitioners in these settings.

In twin pregnancies, it is very common for one or both babies to be in the breech position. Most often twin babies do not have the chance to turn around because they are born prematurely. If both babies are in the breech position and the mother has gone into labour early, a cesarean section may be the best option. About 30-40% of twin pregnancies result in only one baby being in the breech position. If this is the case, the babies can be born vaginally. After the first baby who is not in the breech position is delivered, the baby who is presented in the breech position may turn itself around, if this does not happen another procedure may performed called the breech extraction. The breech extraction is the procedure that involves the obstetrician grabbing the second twin's feet and pulling him/her into the birth canal. This will help with delivering the second twin vaginally. However, if the second twin is larger than the first, complications with delivering the second twin vaginally may arise and a cesarean section should be performed. At times, the first twin (the twin closest to the birth canal) can be in the breech position with the second twin being in the cephalic position (vertical). When this occurs, risks of complications are higher than normal. In particular, a serious complication known as Locked twins. This is when both babies interlock their chins during labour. When this happens a cesarean section should be performed immediately.

With so few individuals actually surviving until birth, the only treatment option is surgery to try to remove the parasitic twin. Surgery, however, is very dangerous and has been successful only once. The problem with surgical intervention is that the arterial supplies of the head are so intertwined that it is very hard to control the bleeding, and it has been suggested that cutting off the parasitic twin's arterial supply might improve the odds of the developed twin's survival.

If locked twins are diagnosed in early delivery, before either twin is born, both fetuses can be delivered by Caesarean section. If one fetus has been partially born, attempts can be made to disimpact the twins manually, such as by the Zavanelli maneuver, with a view to performing an assisted delivery with ventouse or forceps. If the diagnosis is made only after the first locked twin has died in the birth canal, or if it is not expected to survive, the first twin may be decapitated and its head pushed up to allow safe delivery of the second twin.

At least one case has been reported where hexoprenaline was used to relax the uterine smooth muscle and thereby temporarily inhibit labour so that the fetal heads could be disimpacted.

Since locked twins are often diagnosed in the late stages of delivery, it is often too late to intervene to save the life of the first twin and thus there is a high rate of stillbirth, estimated to be over 50%.

Umbilical cord prolapse should always be considered a possibility when there is a sudden decrease in fetal heart rate or variable decelerations, particularly after the rupture of membranes. With overt prolapses, the diagnosis can be confirmed if the cord can be palpated on vaginal examination. Without overt prolapse, the diagnosis can only be confirmed after a cesarean section, though even then it will not always be evident at time of procedure.

The treatment depends on the cause.

Severely anemic fetuses, including those with Rh disease and alpha thalassemia major, can be treated with blood transfusions while still in the womb. This treatment increases the chance that the fetus will survive until birth.

A vanishing twin, also known as fetal resorption, is a fetus in a multi-gestation pregnancy which dies in utero and is then partially or completely reabsorbed. In some instances, the dead twin will be compressed into a flattened, parchment-like state known as "fetus papyraceus".

Vanishing twins occur in up to one out of every eight multifetus pregnancies and may not even be known in most cases. "High resorption rates, which cannot be explained on the basis of the expected abortion rate...suggest intense fetal competition for space, nutrition, or other factors during early gestation, with frequent loss or resorption of the other twin(s)."

In pregnancies achieved by IVF, "it frequently happens that more than one amniotic sac can be seen in early pregnancy, whereas a few weeks later there is only one to be seen and the other has 'vanished'."

Diagnosis may be delayed for several months because the infant's early behavior appears to be relatively normal. Transillumination, an examination in which light is passed through body tissues, can be used to diagnose hydranencephaly. An accurate, confirmed diagnosis is generally impossible until after birth, though prenatal diagnosis using fetal ultrasonography (ultrasound) can identify characteristic physical abnormalities that exist. Through thorough clinical evaluation, via physical findings, detailed patient history, and advanced imaging techniques, such as angiogram, computerized tomography (CT scan), magnetic resonance imaging (MRI), or more rarely transillumination after birth are the most accurate diagnostic techniques. However, diagnostic literature fails to provide a clear distinction between severe obstructive hydrocephalus and hydranencephaly, leaving some children with an unsettled diagnosis.

Preliminary diagnosis may be made in utero via standard ultrasound, and can be confirmed with a standard anatomy ultrasound. This sometimes proves to provide a misdiagnosis of differential diagnoses including bilaterally symmetric schizencephaly (a less destructive developmental process on the brain), severe hydrocephalus (cerebrospinal fluid excess within the skull), and alobar holoprosencephaly (a neurological developmental anomaly). Once destruction of the brain is complete, the cerebellum, midbrain, thalami, basal ganglia, choroid plexus, and portions of the occipital lobes typically remain preserved to varying degrees. Though the cerebral cortex is absent, in most cases the fetal head remains enlarged due to the continued production by the choroid plexus of cerebrospinal fluid that is inadequately reabsorbed causing increased intracranial pressure.

The use of the so-called Solomon technique or dichorionization in fetoscopic laser therapy for TTTS is proven to be beneficial in preventing post-laser TAPS. With this technique, not only all anastomoses are coagulated but also a line is drawn between those in order to coagulate anastomoses that might not (yet) be visible during fetoscopy. It should be stressed that the success of such a technique is highly dependent on the specific situation. For example, when one of the fetusses obstructs the view on the vascular equator (the part of the placenta where the anastomoses need to be coagulated), complete dichorionization by the Solomon technique might not be possible.

Different stages of TAPS are identified using the criteria as shown in the following tables.

Once a child is born prematurely, thought must be given to decreasing the risk for developing NEC. Toward that aim, the methods of providing hyperalimentation and oral feeds are both important. In a 2012 policy statement, the American Academy of Pediatrics recommended feeding preterm infants human milk, finding "significant short- and long-term beneficial effects," including reducing the rate of NEC by a factor of two or more.

A study by researchers in Peoria, IL, published in "Pediatrics" in 2008, demonstrated that using a higher rate of lipid (fats and/or oils) infusion for very low birth weight infants in the first week of life resulted in zero infants developing NEC in the experimental group, compared with 14% with NEC in the control group. (They started the experimental group at 2 g/kg/d of 20% IVFE and increased within two days to 3 g/kg/d; amino acids were started at 3 g/kg/d and increased to 3.5.)

Neonatologists at the University of Iowa reported on the importance of providing small amounts of trophic oral feeds of human milk starting as soon as possible, while the infant is being primarily fed intravenously, in order to prime the immature gut to mature and become ready to receive greater oral intake. Human milk from a milk bank or donor can be used if mother's milk is unavailable. The gut mucosal cells do not get enough nourishment from arterial blood supply to stay healthy, especially in very premature infants, where the blood supply is limited due to immature development of the capillaries, so nutrients from the lumen of the gut are needed.

A Cochrane review published in April 2014 has established that supplementation of probiotics enterally "prevents severe NEC as well as all-cause mortality in preterm infants."

Increasing amounts of milk by 30 to 40 ml/kg is safe in infant who are born weighing very little. Not beginning feeding an infant by mouth for more than 4 days does not appear to have protective benefits.

Data from the NICHD Neonatal Research Network's Glutamine Trial showed that the incidence of NEC among extremely low birthweight (ELBW, <1000 g) infants fed with more than 98% human milk from their mothers was 1.3%, compared with 11.1% among infants fed only preterm formula, and 8.2% among infants fed a mixed diet, suggesting that infant deaths could be reduced by efforts to support production of milk by mothers of ELBW newborns.

Research from the University of California, San Diego found that higher levels of one specific human milk oligosaccharide, disialyllacto-N-tetraose, may be protective against the development of NEC.

The primary concern with umbilical cord prolapse is inadequate blood supply, and thus oxygen, to the fetus if the cord becomes compressed. The cord can become compressed either due to mechanical pressure (usually from the presenting fetal part) or from sudden contraction of the vessels due to decreased temperatures in the vagina in comparison to the uterus. This can lead to death of the fetus or other complications.

Historically, the rate of fetal death in the setting of cord prolapse has been as high 40%. However, these estimates occurred in the context of home or births outside of the hospital. When considering cord prolapses that have occurred in inpatient labor and delivery settings, the rate drops to as low as 0-3%, though the mortality rate remains higher than for fetuses without cord prolapse. The reduction in mortality for hospital births is likely due to the ready availability of immediate cesarean section.

Many other fetal outcomes have been studied, including Apgar score (a quick assessment of a newborn's health status) at 5 minutes and length of hospitalization after delivery. While both measures are worse for newborns delivered after cord prolapse, it is unclear what effect this has in the long-term. Relatively large studies that have tried to quantify long-term effects of cord prolapse on children found that less than 1% (1 in 120 studied) suffered a major neurologic handicap, and less than 1% (110 in 16,675) had diagnosed cerebral palsy.

Craniopagus parasiticus is an extremely rare type of parasitic twinning occurring in about 4 to 6 of 10,000,000 births. In craniopagus parasiticus, a parasitic twin head with an undeveloped body is attached to the head of a developed twin. Fewer than a dozen cases of this type of conjoined twin have been documented in the literature. Most infants with this condition are stillborn, or die shortly after birth.

A parasitic twin (also known as an asymmetrical or unequal conjoined twin) is the result of the processes that also produce vanishing twins and conjoined twins, and may represent a continuum between the two. Parasitic twins occur when a twin embryo begins developing in utero, but the pair does not fully separate, and one embryo maintains dominant development at the expense of its twin. Unlike conjoined twins, one ceases development during gestation and is vestigial to a mostly fully formed, otherwise healthy individual twin. The undeveloped twin is defined as parasitic, rather than conjoined, because it is incompletely formed or wholly dependent on the body functions of the complete fetus.

The independent twin is called the autosite.

There are two main theories about the development of fetus in fetu.

The diagnosis is usually suspected clinically but often requires the aid of diagnostic imaging modalities, most commonly radiography. Specific radiographic signs of NEC are associated with specific Bell's stages of the disease:

Bell's stage 1/Suspected disease:

- Mild systemic disease (apnea, lethargy, bradycardia, temperature instability)

- Mild intestinal signs (abdominal distention, increased gastric residuals, bloody stools)

- Non-specific or normal radiological signs

Bell's stage 2/Definite disease:

- Mild to moderate systemic signs

- Additional intestinal signs (absent bowel sounds, abdominal tenderness)

- Specific radiologic signs (pneumatosis intestinalis or portal venous air)

- Laboratory changes (metabolic acidosis, thrombocytopaenia)

Bell's stage 3/Advanced disease:

- Severe systemic illness (hypotension)

- Additional intestinal signs (striking abdominal distention, peritonitis)

- Severe radiologic signs (pneumoperitoneum)

- Additional laboratory changes (metabolic and respiratory acidosis, disseminated intravascular coagulation)

More recently ultrasonography has proven to be useful as it may detect signs and complications of NEC before they are evident on radiographs, specifically in cases that involve a paucity of bowel gas, a gasless abdomen, or a sentinel loop. Diagnosis is ultimately made in 5–10% of very low-birth-weight infants (<1,500g).

There is no standard treatment for hydranencephaly. Treatment is symptomatic and supportive. Hydrocephalus may be treated with surgical treatment of a shunt, which often grants a much better prognosis and greater quality of life.

The prognosis for children with hydranencephaly is generally quite poor. Death often occurs in the first year of life, but other children may live several years.

Medical text identifies that hydranencephalic children simply have only their brain stem function remaining, thus leaving formal treatment options as symptomatic and supportive. Severe hydrocephalus causing macrocephaly, a larger than average head circumference, can easily be managed by placement of a shunt and often displays a misdiagnosis of another lesser variation of cephalic condition due to the blanketing nature of hydrocephalus. Plagiocephaly, the asymmetrical distortion of the skull, is another typical associated condition that is easily managed through positioning and strengthening exercises to prevent torticollis, a constant spasm or extreme tightening of the neck muscles.

Antenatal corticosteroids have a role in reducing incidence of germinal matrix hemorrhage in premature infants.

A "fetus in fetu" can be considered alive, but only in the sense that its component tissues have not yet died or been eliminated. Thus, the life of a "fetus in fetu" is akin to that of a tumor in that its cells remain viable by way of normal metabolic activity. However, without the gestational conditions "in utero" with the amnion and placenta, a "fetus in fetu" can develop into, at best, an especially well differentiated teratoma; or, at worst, a high-grade metastatic teratocarcinoma. In terms of physical maturation, its organs have a working blood supply from the host, but all cases of "fetus in fetu" present critical defects, such as no functional brain, heart, lungs, gastrointestinal tract, or urinary tract. Accordingly, while a "fetus in fetu" can share select morphological features with a normal fetus, it has no prospect of any life outside of the host twin. Moreover, it poses clear threats to the life of the host twin on whom its own life depends.