Fetal Surgery for Spina Bifida: Benefits, Risks, and Timing

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• The Two-Hit Hypothesis of Spinal Damage
• Benefits of Fetal Surgery for Spina Bifida
• Risks of Prematurity and Membrane Rupture
• Optimal Timing for Fetal Surgery
• Postoperative Pregnancy Care and Delivery
• Global Implications for Spina Bifida Treatment
• Full Transcript

The Two-Hit Hypothesis of Spinal Damage

Dr. Yves Ville, MD, describes the two-hit hypothesis that underpins the rationale for fetal spina bifida surgery. The first hit is the congenital malformation itself, where the spinal cord is exposed. The second hit is the continuous exposure of the unprotected neural tissue to amniotic fluid. Amniotic fluid is chemically aggressive and causes further damage to the exposed spinal cord. This secondary injury worsens the overall lesion and neurological outcome for the baby.

Benefits of Fetal Surgery for Spina Bifida

The primary goal of fetal surgery is to protect the spinal lesion from the toxic effects of amniotic fluid. Dr. Yves Ville, MD, explains that covering the defect in utero can halt this secondary damage. A significant benefit is that a good proportion of babies do not require a major reoperation after birth. Some may only need a smaller procedure later for a tethered spinal cord. This intervention offers a tangible benefit for families who choose to continue the pregnancy.

Risks of Prematurity and Membrane Rupture

A major risk of any fetal endoscopic surgery is preterm premature rupture of membranes (PPROM). This complication can lead to significant prematurity. Dr. Yves Ville, MD, notes that the relationship is complex; moderate prematurity might actually reduce amniotic fluid exposure time. However, extreme prematurity is life-threatening. He states that about 15% of fetuses see a clear benefit from the surgery. Conversely, 5% to 10% may not benefit and could potentially have a worse outcome.

Optimal Timing for Fetal Surgery

The timing of fetal surgery is critical for its success and safety. Dr. Yves Ville, MD, emphasizes that the ideal window is mid-pregnancy, between 20 and 25 weeks of gestation. Operating too early increases the risk of complications like membrane rupture. Operating too late, after 30 weeks, offers little benefit as the damage may be irreversible. At that stage, it is often better to plan for delivery and perform postnatal surgery instead.

Postoperative Pregnancy Care and Delivery

Dr. Yves Ville, MD, highlights a key advantage of endoscopic over open fetal surgery: postoperative care. After an endoscopic procedure, the pregnancy care is not significantly different. The mother does not need to remain hospitalized continuously and can often return home. Furthermore, vaginal delivery is still an option. This is a stark contrast to open fetal surgery, which always necessitates a Cesarean section for delivery, even if labor begins extremely early.

Global Implications for Spina Bifida Treatment

Dr. Yves Ville, MD, discusses the global importance of this minimally invasive approach. In developing countries, access to immediate, complex postnatal surgery can be limited. Performing the surgery in utero means the baby could be born anywhere, even in a remote setting, without immediate risk. This is crucial in regions where perinatal infection before or after postnatal surgery is a major concern. Fetal surgery could therefore provide a vital treatment pathway worldwide.

Full Transcript

Dr. Anton Titov, MD: Spina bifida can be diagnosed in unborn children. You already mentioned some of it. You are an expert in fetal surgery and in utero endoscopic surgery. Fetal surgery can be done on an unborn child with spina bifida, which, you already mentioned, doesn't remove the spina bifida. Nevertheless, there are some indications for fetal surgery for spina bifida. Could you please summarize the benefits and risks of doing the endoscopic fetal surgery in situations where spina bifida is discovered before the birth of a child?

Dr. Yves Ville, MD: The advantage of intrauterine surgery for spina bifida is that you prevent, on top of the malformation, the deleterious effect of the aggressivity of amniotic fluid on the exposed spine. Because the fetal spine is not protected by the bones nor the skin. So the amniotic fluid is quite aggressive on this spine. It worsens the lesion and the effect.

It's called the two-hit hypothesis. One is malformation. The second is the aggressiveness or toxicity of the amniotic fluid on the spinal lesion. So you help by protecting the spinal lesion. A good proportion of these babies do not need to be reoperated after birth, or sometimes they have a tethered spinal cord. And then it's a smaller operation than the whole spina bifida repair.

So it's mainly to prevent that amniotic fluid-related morbidity. And that's probably why the effect of intrauterine surgery is not that major compared to postnatal surgery. But that helps. So for women who want to carry on with the pregnancy, which is not considering termination of pregnancy, that fetal surgery can help.

The downside is the risk of prematurity because of the rupture of membranes. As for all endoscopic surgery, mainly, and therefore risks of prematurity. But prematurity for spina bifida is kind of an open question. Apart from extremely premature delivery, where this is life-threatening, if that prematurity is moderate, it might be that this has a positive effect because there is less exposure of the baby to the amniotic fluid also.

The relationship between all these is not very clear. But basically, you want to go ahead with your pregnancy. And you want to gain that little benefit, which is for 15 percent of the fetuses seem to benefit from intrauterine surgery. In contrast, about five to 10% of fetuses with spina bifida do not benefit from fetal surgery and get worse. So the balance is quite thin to find.

Dr. Anton Titov, MD: What is the typical timing for the spina bifida surgery in relation to the pregnancy? How much time usually passes before the delivery of baby after fetal endoscopic surgery?

Dr. Yves Ville, MD: For all fetal surgery, there are two phases. Too early, and you get a very high rate of complications like rupture of membranes. So you have to do fetal endoscopic surgery about mid-pregnancy, between 20 and 25 weeks of pregnancy, of gestation is the right time. And that is true for all surgery.

That's when the uterus is more tolerant of the aggression of the instruments. And that's when also the lesions are not that irreversible, probably, or not yet at a stage where no improvement can be expected. It will not make sense to operate on a fetus at 30 weeks of pregnancy, for example, for any fetal surgery. It is better to deliver the baby or the babies and do surgery after birth or just save them from twin-to-twin transfusion, for example.

So then the attempt is to carry a pregnancy for another essentially ten weeks. So that's what you expect a good two months in utero to grow, mature, and not be exposed to the lesions.

Dr. Anton Titov, MD: Does the pregnancy care after uterine surgery and fetal surgery differ significantly in those ten weeks? So what is the average?

Dr. Yves Ville, MD: No, usually, that's an advantage of endoscopic surgery over open uterine surgery. If you do open surgery, there's no other way than Cesarean section, even if this woman gets into labor very early in gestation. Whereas if you operate endoscopically, she can deliver normally or vaginally at least anytime. And the care is not different.

So you don't have to stay continuously in the hospital. You could be at home, doing a usual obstetrical follow-up. Not when the fetal endoscopic surgery is a one-shot thing. If you were thinking of what we were discussing about diaphragmatic hernia with a balloon that obstructs the trachea, then this baby cannot be born anywhere.

The baby has to be born somewhere, either ideally after removing the balloon in utero. Or it is required to remove the balloon at birth by a very experienced team. So that's a different ballgame. But the spina bifida baby could be born in a back garden, that's not a problem, which might be an advantage for developing countries because this is a global problem.

And in some countries where postnatal surgery of this condition exposes to perinatal infection before and after surgery after birth. It might be a good thing that these babies are operated on before they are born. That's a very important point.

Dr. Anton Titov, MD: Thank you.