During the early days of pregnancy, amniocentesis is carried out on pregnant woman to find out if the developing fetus is free from certain abnormalities. This procedure involves certain invasive methods like inserting a hollow needle into the uterus of the woman through her abdominal wall to withdraw a sample of amniotic fluid that surrounds the fetus. Using ultrasound, the location of the fetus floating in the amniotic fluid is determined. The abdominal skin surrounding the area is cleaned. The procedure may be conducted either by injecting a local anesthetic in that area, or by just applying a tropical anesthetic around the area through which the needle is to be inserted. About 1 cc per week of gestation of the fetus is taken out from the amniotic fluid.
This procedure is used as a tool which can detect chromosomal disorders like Downs Syndrome and many rare metabolic disorders which are normally inherited. Some structural defects like spina bifida and anencephaly can be detected using this test. This procedure is normally carried out for women over the age of thirty five. It is recommended for women who had undergone a triple screen blood test during pregnancy and for those who have a family history of birth defects or some inherited metabolic disorders. This procedure may be conducted even in later stages of pregnancy to detect suspected problems like Rh incompatibility or infection. This test is also used to determine lung maturity of the infant in the last trimester.
A cell culture is done with the fetal cells taken out during the procedure and the analysis of the DNA is conducted to detect chromosomal abnormalities. It may take up to a month for the results to arrive. This is rated as a highly accurate procedure.
After the withdrawal of the amniotic fluid which takes only a few minutes, the pregnant woman is advised to be in bed for several hours, though the entire procedure will last for about 45 minutes. Doctors check the heart beat of fetus to ensure that it is normal. It is wise to call the health care provider, if the woman experiences fever, bleeding or leakage of amniotic fluid for a long time. Though the chances of infection or injury to the fetus are not ruled out, they are quite rare. There is also a slight chance of miscarriage, but the percentage is negligible. During later stages of pregnancy, a Doppler ultrasound is safer than amniocentesis because it is non-invasive. Anemia in the fetus can easily be detected using ultrasound by measuring the velocity of the blood flow in the middle cerebral artery.
Fetal surgery refers to the surgical treatment of the developing baby in the womb to rectify congenital defects. Surgery of the fetus is performed to fix the prenatally diagnosed anomalies. However fetal surgery is a complicated procedure and comes with lot of risks to both mother and the baby. Yet, doctors recommend fetal surgery, if the risks associated with continuing the pregnancy, without surgical intervention, outweighs the risks that come with fetal surgery. Certain abnormalities, if left to progress in the womb, may turn fatal and infant may die soon after the birth. However fetal intervention is initiated only after taking the safety of the mother into consideration. The common risks that are associated with fetal surgery are premature delivery, infection of the uterus, leaking of amniotic fluid through the membrane, potential infertility and the risk of anesthesia.
There are various techniques followed to diagnose fetal anomalies. The diagnostic method can be non invasive such as ultrasound, fetal echocardiography, MRI, Radiography, Measuring MSAFP (maternal serum alpha-fetoprotein) and Measuring maternal serum beta-human chorionic gonadotropin (HCG) or invasive procedure such as amniocentesis, Chorionic villus sampling and Percutaneous umbilical blood sampling (PUBS) are used to detect the birth defects.
Types of Fetal Surgery
Depending on the incision level, fetal surgery is classified into three types.
Open Fetal Surgery
Open fetal surgery is almost similar to cesarean section and involves a total opening of the uterus. In this type of surgery, a long incision is made in the mother's abdomen and then on the uterus to reach the fetes. Once the surgical correction is performed on the fetus to treat the birth defect, the uterus and abdominal is closed back leaving the fetus intact. Open fetal surgery is performed under general anesthesia. Surgery is performed using special instruments containing staples to prevent bleeding from uterus. During the operation, warm saline water is infused to maintain the position of placenta and umbilical cord and surgeon will keep a vigil on the pulse and heart rate of the baby with the help of the oximeter. After the surgery, the mother is hospitalized for close to a week to facilitate close monitoring. One should remember that, with open fetal surgery, mother will forgo the option of vaginal delivery for the present and future deliveries. She can deliver the baby only through C-section. She may be given some medication to avoid pre term labor. Open fetal surgery is followed for the conditions like chest mass, neck mass, spinbifida, myelomeningocele and Sacrococcygeal teratoma (SCT) (a tumor at the base of the child's tail bone).
There is one more variation to the open fetal surgery called the EXIT (Ex Utero Intrapartum Treatment) Procedure. EXIT surgery is performed at the end of the full term and just before the delivery. In this method the baby is partially delivered by bringing out only a part of the fetes from uterus and keeping rest of the fetes attached to placenta and umbilical cord to allow blood circulation. Once the defect is rectified, the baby is delivered fully. Exit procedure is essentially followed to correct the airway blockage in the baby.
Fetoscopic surgery is minimally invasive and unlike open fetal surgery, fetes remains inside the uterus while operating. Surgeon uses special instruments such as laser and makes a small incision with the help of the fetoscope to correct the birth defects. Fetoscopic surgery has shown high success rate in conditions such as Twin-Twin Transfusion Syndrome (TTTS), Twin Reversed Arterial Perfusion (TRAP), Amniotic band syndrome, and Tracheal occlusion for CDH. Fetoscopic surgery does not pose a risk of pre term labor and also eliminates most of the risks associated with open fetal surgery. This is essentially why fetoscopic surgery is the preferred choice, yet one should note that few complicated birth defects can be corrected only through open fetal surgery.
Fetal image guided surgery
Fetal image guided surgery is the least invasive of all wherein surgery is performed with the guidance of images of fetus produced on the external screen by ultrasound. Very thin instruments are inserted through a small opening in the abdomen and the correction is made without any endoscopic view and the whole procedure is guided by the sonogram images.
Various congenital conditions treated through fetal intervention
Congenital diaphragmatic hernia (CDH): Congenital diaphragmatic hernia (CDH) refers to the opening in the diaphragm through which the contents of the abdomen enter the chest cavity leaving no space for the lungs to develop properly. This is a serious condition and may lead to respiratory failure after birth. This condition, depending upon its severity, is treated through fetal intervention.
Spina bifida: Spina bifida refers to a condition wherein spinal column of the baby does not close properly around the spinal cord and the nerves start to protrude through the opening. Spina bifida can range from mild to severe form, and the severe cases lead to serious neurological problems after the birth. Only the severe form of spina bifida like Meningocele and Myelomeningocele call for fetal intervention through open fetal surgery.
Neck masses: Neck masses are the tumors of the neck that may obstruct the airway and esophagus of the child and also increase the level of amniotic fluid surrounding the baby. Typically, tumors of any kind are treated after birth. In rare cases they grow very large and may even cause heart failure. In such cases fetal intervention becomes necessary to remove the tumors.
Lung lesions: Lung lesions refer to the abnormal growth of lung tissue and these lesions can be cystic (fluid filled) or solid. There are various types of lung lesions and treatment depends upon their size and location. During pregnancy, continuous monitoring is necessary to keep vigil on the size of the lesion. Most often lung lesions shrink and make way for normal development. Lesions of smaller and moderate size are best treated after delivery. But if the size of the lung tumor is abnormally huge and poses a risk of hydrops (excess accumulation of fluid in the fetus) fetal intervention is initiated. Cystic lesions are normally removed through needle aspiration under the constant guidance of ultrasound images, but solid lesions require more elaborate procedure such as EXIT.
Congenital heart diseases: Not all congenital heart defects call for fetal intervention. Sometimes the septum (wall separating the right and left side of the heart) of the heart develops a hole while in the womb. However septum defects are typically treated after the birth of the child and rarely require fetal surgery. But if the heart develops severe obstructive cardiac disorders such as aortic stenosis, pulmonary stenosis and coarctation of the aorta,a fetal image-guided procedure may be necessary to open or enlarge the narrowed valve. This procedure involves placing a balloon catheter by inserting it through the uterus and into the fetal’s heart.
Amniotic Band Syndrome: This is a condition where fetus is entrapped in fibrous amniotic bands in the womb, restricting blood flow to the affected portion of the fetes. It normally affects legs, arms, toes and fingers. In utero surgery may be performed to rectify the condition if there is risk of amputation of the limb after the birth.
Twin-to-twin transfusion syndrome (TTTS): TTTS is a condition that occurs in identical twins wherein unbalanced exchange of blood takes place between the twins. One receives higher amount of blood whereas the other receives less amount. The fetus with less blood supply may become anemic and the one with excess blood supply may suffer heart failure due to excess fluid. Fetal surgery through laser fetal intervention is the preferred option to correct the condition. This procedure involves inserting a laser along with small telescope into the uterus and separating the blood vessels on the placenta that are connected to both twins.
Congenital high airway obstruction syndrome (CHAOS): Congenital high airway obstruction syndrome (CHAOS) refers to the blocking of fetal airway resulting in enlarged lungs, windpipe and bronchial tube. A complete or near to complete blockage may lead to a heart failure. Though congenital high airway obstruction syndrome (CHAOS) is treated after birth, in severe cases where fetes is at high risk such as hydrops, fetal surgery is performed.
Acrania is a rare congenital abnormality characterized by complete or partial absence of flat bones of cranial vault (skull bones) in the human fetus. However brain tissue of fetus develops completely but abnormally. The cranial vault, or calvarium, surrounds and encloses the brain, and is formed from several plates of bone like parietal, squamosal, occipital, temporal, and frontal bones above the supraciliary ridge. In the embryo, the vault bones develop through ossification of the ectomeninx, the outer membranous layer surrounding the brain. The normal migration of mesenchymal tissue under the calvarial ectoderm should occur by the 4th week of gestation. However the closing of anterior neuropore and lack of mesenchymal migration (responsible for cranium formation) in the fourth week of embryological age results in Acrania.
With the absence of the skull, brain floats in the amniotic fluid over the base of skull. Increased amount of amniotic fluid is usually observed. Without the bony structure, the overlying ectoderm, as a thin amnion-like membrane covers the brain tissue.The fetus will generally have normal facial structures.
Acrania is always associated with severe condition called Anencephaly where most of the brain portions are absent along with skull and scalp. In most cases, Acrania progresses to Anencephaly, because, without the cranium, the cerebral tissue is exposed and thus gets degenerated resulting in eventual loss.
Diagnosis of Acrania
Acrania can be diagnosed early in pregnancy through an ultrasound. This anomaly appears during the the fourth week of the fetus's development. However The fetal cranium is not fully calcified before 10–11 weeks; therefore, diagnosis must be confirmed only after 11th week.
There is no treatment for Acrania. The condition is termed as incompatible with life. If at all the fetus survives the term, babies are either still born or die within few hours of birth. Since Acrania is a fatal pathology, medical abortion, as soon as the confirmed diagnosis, is suggested. This will help minimize medical interventions and also reduce the emotional agony to the mother and the family.
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Bibliography / Reference
Collection of Pages - Last revised Date: April 20, 2021