Seal pregnancies reveal clues for treating birth complications

Wild animals, shaped by evolution, are adapted to survive in harsh ecosystems. These adaptations may now hint at solutions to human reproductive health and pregnancy challenges.

Dr. Michelle Shero, assistant scientist at Woods Hole Oceanographic Institution (WHOI), has explored this link through the study of seals.

“When people think about biomedical research, they probably don’t immediately think about wildlife such as birds, cheetahs, bears, or seals – but they should,” said Shero.

Fasting seals and pregnancy diabetes

Human pregnancy involves complex metabolic changes. One problematic condition that arises fairly commonly is gestational diabetes mellitus (GDM), which affects up to 25% of pregnancies.

It usually resolves after childbirth but can have lasting effects on both mother and baby. Conventional medicine treats GDM with diet, exercise, or medication, all aimed at lowering maternal blood glucose levels.

Marine mammals take a different path. Phocid seals, such as the Weddell or hooded seal, enter a fasting state during reproduction. They stop eating altogether while nursing, and lose up to 40% of their body mass.

Despite this, both mothers and pups thrive. This remarkable strategy hinges on reversible insulin resistance – a condition that looks like GDM but causes no harm.

Unlike humans, fasting seals maintain high blood sugar levels without accumulating ketones or damaging tissues. Their insulin levels stay low. Glucose continues circulating, and supports energy needs without tipping into metabolic dysfunction.

This balance results from finely tuned hormonal shifts and tissue-specific insulin responses.

Sugar transfer in seal pregnancies

In humans, high maternal glucose levels lead to excessive fetal growth and complications. Seals flip this script.

In Weddell seals, the fetus has higher glucose levels than the mother. This shift happens due to unique blood cell glucose ratios and slow glucose turnover.

These features suggest a controlled nutrient transfer that supports the fetus without risking overgrowth. Learning from this could improve treatments for gestational diabetes in humans.

How seals survive with low oxygen

Seals dive deep, holding their breath for hours. Their bodies can stockpile oxygen and use it with surgical precision. Blood flow prioritizes the brain, heart, and uterus while cutting supply to muscles.

“What marine mammals do to make it possible for them to dive for so long is really amazing,” said Shero.

“This is even more incredible when we consider the fact that every time the adult seal dives, her fetus is brought along and responds in much the same way on all those dives too.”

Marine mammals maintain this dive reflex even under extreme oxygen deprivation. Their bodies withstand arterial oxygen pressures that would knock humans unconscious. They also avoid tissue damage during reoxygenation through powerful anti-inflammatory responses.

Protecting human fetuses from hypoxia

During birth, some babies can experience oxygen deprivation, which may lead to lifelong damage. Currently, humans rely on cesareans and heart rate monitoring to avoid this dangerous situation.

Seals offer a better model as their pregnancy includes repeated, deep fetal hypoxia. Learning their strategies could reshape approaches to neonatal care.

Adaptations like splenic contractions, vascular shunting, and blunted nitric oxide responses may hold keys. Seals also collapse their lungs underwater to prevent nitrogen toxicity, then re-expand them with surfactant-rich linings.

Pressing pause on pregnancy

Another adaptation that seals show is embryonic diapause. After mating, many pinnipeds delay embryo implantation. This ensures pups are born during optimal conditions. In some species, diapause can last months.

Shero noted that this ability may exist in other mammal species, including humans. “Learning how to ‘hit pause’ on pregnancy until conditions are optimal, like seals do, would be a breakthrough,” she explained.

Natural embryo pause vs. freezing

Current IVF protocols freeze embryos. This can damage DNA and lower success rates. If doctors could trigger a safe metabolic pause like diapause, embryos could wait for the best moment to implant.

Reciprocal studies show that sheep embryos paused in a mouse uterus resume normal development. This points to a shared mechanism among mammals. One rare IVF case even documented a human embryo in diapause for five weeks.

What seals teach us about pregnancies

Seals survive under pressure – literally and figuratively. Their biology can reshape our understanding of what’s “normal” in health.

“In seeking ways to improve human health, we should be looking to the extraordinary feats of wild animals – they have often found the most innovative solutions,” Shero concluded.

This research was supported by the Every Page Foundation and other science bodies, including NSF and WHOI.

The study was published in the journal F&S Reports.

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