A pioneering Johns Hopkins Medicine study advances understanding of how amniotic membranes can be damaged during fetal surgeries — information that could advance care for high-risk pregnancies by reducing preterm births after such procedures.

Over the past 40 years, fetoscopic surgeries have become more common and more sophisticated, frequently yielding near-miraculous results in treating conditions including twin-to-twin transfusion syndrome, spina bifida and diaphragmatic hernia. 

Yet, up to 40% of these in-vivo procedures result in iatrogenic preterm prelabor rupture of membranes (iPPROM), which can lead to premature births and even pregnancy loss.

A new Johns Hopkins study, published in June in Prenatal Diagnosis, appears to be the first to show that membrane damage that leads to these ruptures can be dramatically reduced by using a strategy of gradual expansion of the entry instead of the fixed-diameter sheathed trocars to perform the surgeries.

Co-author Ahmet Baschat, director of the Johns Hopkins Center for Fetal Therapy, says the finding provides potentially lifesaving information for surgeons and patients, on a topic that has previously received too little attention.

“Research into amniotic membranes has been under-emphasized,” he says. “Not a lot was understood about the membrane and what governs its integrity, how it gets damaged, and if there is a way to minimize the damage.”

Baschat, one of the nation’s top maternal-fetal medicine specialists, explains that fetal surgeries require entry through the uterine muscle and amniotic membrane. This intrusion is the primary cause of rupture because the membrane does not have the ability to heal.

Most fetoscopic surgeons use trocars to create access points through the membrane large enough for the procedures. An alternative is to puncture the membrane with a needle and then slowly widen it with a balloon.

With no existing evidence-based comparisons, Baschat tapped Johns Hopkins biomedical engineers Selena Shirkin, Alice Yu and Eric McAlexander, as well as Jason Murray in the Department of Pathology, to study membrane disruptions.

For the experiment, they used amniotic membranes from placentas of healthy patients who had already delivered, and punctured them with 2 mm and 4 mm sheathed trocars, and with an angioplasty balloon that expanded from 2 mm to 4 mm. The results clearly showed that the smaller diameter balloon procedure with subsequent dilation, known as the Seldinger technique, reduced membrane damage, says Baschat.

The Seldinger technique takes a minute or two longer, and requires specialized skills and equipment. The study’s findings, says Baschat, could prompt the development of equipment that takes this new information into account. “If you want to develop a new port system for fetal surgery, it should really be a radially expanding device that goes in with a smaller diameter,” he says. 

Meanwhile, Baschat says the study has already prompted him to use the Seldinger technique when operating. “We can’t eliminate every risk associated with fetal surgery, but when evidence points to a way to reduce one of the biggest ones, you pay attention,” he says.