<http://schema.org/description>
"Yes, generally, twins and other multiples are born earlier than singletons. One report said 60% of twins were born preterm (under 37 weeks of gestation)"^^<http://www.w3.org/2001/XMLSchema#string>
<https://www.verywell.com/are-twins-born-earlier-than-single-infants-2447481>