The risks of twin foals

The arrival of twin foals tends to hit headlines. When breeding mare Didi Van Weltevreden delivered not just one foal this spring but two, her connections were certainly surprised.

“We hadn’t realised that she was carrying a twin foal, until the birth,” says Marjolijn Takke of Beukestein Stables in Maartensdijk, the Netherlands. “She had developed a really big belly towards the end of her pregnancy, but the vet told us that was normal as the mare is big.

“When the filly foal arrived and was not that large, we joked that there might be another one in there,” Marjolijn continues. “Then Didi started to labour again and delivered the second foal, a colt.”

Didi’s double delivery is indeed remarkable, according to Dr Charles Cooke MRCVS of Equine Reproductive Services.

“As a prey animal, a newborn foal must be ready to leap to his feet and run,” he explains, pointing out that other baby mammals that have the “pack” to protect them remain helpless, with their eyes shut, for some time. “To ensure this happens, the mare’s placenta provides all the foetus needs but will only really sustain one foal satisfactorily. Twin pregnancies can occur, however, when a mare ovulates an egg from each of two follicles and both eggs are fertilised.

“Carrying twins is risky,” adds Charles. “It is essential that the mare has an ultrasound scan 15-16 days after covering to see if she is in foal, address any twin/triplets or prepare her for re-covering if she isn’t pregnant — and another at around 18-20 days if there is any evidence or suspicion of a second pregnancy. Some mares are also scanned at 28 days to confirm a single, healthy foetus.”

Twin foals: the chances of survival

While some twin pregnancies may reduce to a single spontaneously in the first few weeks, Charles explains that prompt action is preferable. It is usual for the vet to “squeeze” (crush) one by hand at the 15-16 day exam, when the procedure is relatively simple and has minimal effect on the remaining embryo.

Didi was scanned several times by the vet during her early pregnancy, yet a second embryo was never spotted. How does a twin foal remain undetected?

“Identifying a twin pregnancy can be difficult” explains Charles. “A pregnancy can be surprisingly similar to a uterine cyst, which is a dilation of soft tissue in the uterus, so an embryo nestled up against cysts can ‘blend in’. Repeat scans can help.”

“If the embryos settle next to each other at the base of the same uterine horn [arm], they are in competition for space and nutritional contact with the uterus. They might both be lost or reduce spontaneously, although this cannot be relied upon and happens later than the 15-16 day vet squeeze. Manual reduction is always the best option for a single, healthy pregnancy. Those in separate horns can develop independently, which usually leads to problems in mid-late pregnancy.

“Complications include musculoskeletal issues for the mare, uterine trauma and infection, or abortion with possible ‘dystocia’ [delivery problems].”

If twins are born live, their combined weight is often the same as the single foal the mare’s uterus is designed to carry, explains Charles. They tend to be very weak with an increased risk of neonatal illness.

“Twin foals are always a worry and are to be avoided where possible, so ultrasound examination in early pregnancy is something we always recommend,” he says. “When they do occur and survive, they are headline news for a reason.”

Ref Horse & Hound; 22 August 2019