Official websites use .gov
A
.gov website belongs to an official
government organization in the United States.
Secure .gov websites use HTTPS
A lock (
) or https:// means you've safely
connected to the .gov website. Share sensitive
information only on official, secure websites.
Cumulative probability of at least one twin birth, as a function of twinning probability (xl = 0.013 blue, and xh = 0.045 red) and number of pregnancies. The horizontal dashed lines show the y-axis intercepts of the numerical examples given in the box.
