Ask anyone who has decorated an entire nursery based on the expected biological sex of their baby only to discover after birth that they need to find all the receipts and tags.
How Long Can Twins Go Undetected? Here's What You Should Know About Mystery Multiples
So the next time someone stops you on the street or at a family brunch to ask if you sure you're not having twins, you can say with certainty: one heartbeat, one baby.
5 Weeks Pregnant With Twins: Symptoms, Belly & Ultrasound
However, to avoid missing a situation of early intrauterine growth restriction in one twin, most experts agree that the clinician may consider dating pregnancy using the larger baby.