Open fetal surgery is an invasive form of fetal intervention in the treatment of birth defects where the pregnant uterus is opened up for direct surgery on the fetus.
Open fetal surgery is similar in many respects to a normal cesarean section performed under general anesthesia, except that the fetus remains dependent on the placenta and is returned to the uterus. A hysterotomy is performed on the pregnant woman. Once the uterus is open and the fetus is exposed, the fetal surgery begins. Typically, this surgery consists of an interim procedure intended to allow the fetus to remain in utero until it has matured enough to survive delivery and neonatal surgical procedures. Upon completion of the fetal surgery, the fetus is put back inside the uterus and the uterus and abdominal wall are closed up.
The mother remains in the hospital for 3-7 days for monitoring and is required to subsequently deliver the baby via a second cesarean section. Often babies who have been operated on in this manner are born pre-term.
Open fetal surgery has proven to be reasonably safe for the mother. For the fetus, safety and effectiveness are variable, and depend on the specific procedure, the reasons for the procedure, and the gestational age and condition of the fetus.
Fetal surgical techniques using animal models were first developed at the University of California, San Francisco in 1980.
In 1981, the first human open fetal surgery in the world was performed at University of California, San Francisco under the direction of Dr. Michael Harrison. The fetus in question had a congenital hydronephrosis, a blockage in the urinary tract that caused the bladder to dangerously extend. To correct this a vesicostomy was performed placing a catheter in the fetus allowing the urine to be released normally. The blockage itself was removed surgically after birth. 
Further advances have been made in the years since this first operation. New techniques have allowed additional defects to be treated and for less invasive forms of fetal surgical intervention such as fetendo and fetal image-guided surgery.
Defects Sometimes Treated by Open Fetal Surgery
- Congenital diaphragmatic hernia (if indicated at all, it is now more likely to be treated by endoscopic fetal surgery)
- Congenital cystic adenomatoid malformation
- Congenital heart disease
- Myelomeningocele (a severe form of spina bifida)
- Pulmonary sequestration
- Sacrococcygeal teratoma