By Lester Holt, NBC News anchor

It's been an unsettling couple of days--from Iran's admission it has a secret nuclear facility under construction and suspicions in the West that it may be for weapons production--to a series of unrelated terror plots here at home.

Tonight we'll be reporting on developments from both fronts, including President Obama's new message to Iran, and new pieces of a plot a terror suspect may have been planning to unleash in New York city.

Plenty of American couples have to turned to in-vitro fertilization in order to have children, but two stories in the news are raising serious questions about how frozen embryos are handled. Tonight we'll tell you about a Louisiana clinic that has apparently mixed up several embryos.  It follows on the heels of an Ohio woman who was accidentally implanted with another couples' embryo.

Thanks for checking in. I hope you will join us for NBC Nightly News.