On the fiftieth day of her pregnancy, Tristan took Kate to the hospital for a checkup.

Kate lay on the bed, and her belly was exposed. She felt the probe of the ultrasound machine moving along her skin, and she held her breath.

The doctor looked at the monitor and said, "…the embryo has the shape of a human now…body segments are forming, and you can see the limbs."

The fetal heart was beating fast, and with the amplifier, it echoed in the confined space of the ...