What is an HBAC?
A vaginal birth after a previous cesarean section is called a VBAC. A home VBAC is often called an HBAC - home birth after cesarean.
Are HBACs riskier than hospital VBACs?
HBACs have nearly four times the newborn death rate that hospital VBACs have. VBACs attempted in the hospital have a neonatal mortality rate of 1.3/1000; this means that one baby will die for about every 800 hospital VBACs attempted. VBACs attempted at home (HBACs) have a neonatal mortality rate of 4.75/1000; this means that one baby will die for about every 200 HBACs attempted.
Why are VBACs considered "high risk"?
In other countries where home births are well-integrated into the medical system and they have regulated risk assessment criteria, having a prior cesarean section means you will be "risked out" of having a home birth. Your pregnancy and labor are considered "high risk." Why is that?
Well, one of the biggest reasons having a prior cesarean section makes you high risk is the increased chance of uterine rupture. In the place where the uterus was cut during the prior cesarean delivery, a scar has formed. The stress of stretching out during pregnancy and then undergoing labor can cause the uterus to tear open at the scar. This is called uterine rupture, and it is a life-threatening event for both mother and baby.
For women who have never had a cesarean section, the uterine rupture rate is only 0.012%, or 1 in 8,434. For women who have had a previous "classic" cesarean section (vertical cut on the uterus), the uterine rupture rate is 2-11%, or at least 1 in 50 (and possibly as high as 1 in 9). For women who have had a previous low transverse cesarean section (the most common kind of cesarean), the uterine rupture rate is 0.5-2%, or about 1 in 200 (but possibly as high as 1 in 50).
What are the signs of a uterine rupture?
Signs of a uterine rupture include abnormal patterns in the baby's heart rate, tachysystolic contractions (that means where the contractions are one right after the other), vaginal bleeding, shock, prolonged labor, and abdominal pain, but by far the most consistent sign of a uterine rupture is abnormal patterns in the baby's heart rate. The absolute best way to watch for this sign is with continuous electronic fetal monitoring, which can only be done in the hospital.
Sometimes CPMs and other home birth midwives claim that they have "better training" than nurses or doctors to detect uterine ruptures. This is not true. It may be possible for a home birth midwife to detect a uterine rupture with a doppler if they are listening for longer intervals than normal and at the exact same time as the rupture, but it's highly unlikely they will catch the rupture right away. It's also a myth that being at home with a midwife will prevent a rupture. It will not. Uterine ruptures occur at the same rate in the hospital and out; it's just far more likely at home that the rupture will go undetected until it is too late for the baby.
If the uterus ruptures, how long do you have to save the baby?
When the uterus ruptures, the biggest risk to the baby is lack of oxygen. Essentially, the baby cannot breathe, and the placenta is no longer providing them with oxygen. They are suffocating. A cesarean section needs to be performed immediately to save the baby from brain damage or death. Several studies have shown that you have at most about 18 minutes to deliver the baby after uterine rupture before certain brain damage or death. You can see those studies here and here.
Many families planning home birth are comforted by the fact that "we live just five minutes from the hospital" in case anything goes wrong. But living five minutes from the hospital means you are at least thirty minutes from an emergency c-section, as this post explains: Five Minutes to the Hospital.
VBAC at the hospital vs. VBAC at home, a summary
At the hospital: A woman is attempting a VBAC with continuous electronic fetal monitoring, the best way to detect a uterine rupture. She does, indeed, rupture. The baby's distress is detected almost immediately and the doctors can act immediately to save the baby's life and brain function.
At home: A woman is attempting a VBAC and the baby's heart rate is being checked every fifteen minutes with a doppler. The midwife checks the baby's heart rate. It sounds good. A few minutes after she checks, a rupture occurs. Fifteen minutes later, she checks again. This time she can tell the baby's distressed. They call the ambulance, which takes a few minutes to arrive and another few minutes to get to the hospital. Some more time (we'll estimate 15 minutes) is spent getting the mom ready for an emergency c-section. By this time, the baby's been without oxygen for over 30 minutes and is most likely lost or at the very least severely brain damaged.
VBACs are classified as "high risk" for a reason.