The "This Is Us" actress and her musician husband Taylor Goldsmith have welcomed their son August, revealing the newborn arrived "right on his due date."
"Gus is here," Mandy wrote on Instagram. "Our sweet boy, August Harrison Goldsmith. He was punctual and arrived right on his due date, much to the delight of his parents."
"We were prepared to fall in love in all sorts of brand new ways, but it goes beyond anything we could have ever imagined."
Mandy recently had to rethink her birth plan after she discovered she has a low platelet count. "Weekly platelet check at the hematologist," she wrote on her Instagram Story. "My platelets have dropped exponentially during pregnancy."
The arrival marks the end of a long journey for Mandy and her husband, who have been trying to conceive for years.
After failing to fall pregnant, the singer and actress visited a fertility doctor and was told that she was suffering from suspected endometriosis - a medical condition that affects the tissue of the uterus and can cause infertility.
"I was fully prepared to go (and) have surgery and fix my uterus and hopefully get rid of the endometriosis, if it was there," she said at the time. "It was nice to have a plan and to know, 'OK, well this is why I haven't been pregnant yet.' "
But Mandy discovered she was pregnant during one appointment with the fertility experts.