mẹ tròn con vuông

Etymology
Perhaps from the ideal shapes of the sky and the earth, rooted in some ancient mythologies that purport that the earth is square and the sky is a dome covering it. See also the Legend of bánh chưng and bánh giày.

Phrase

 * 1)  round mother, squared baby
 * 2)  you/she (have/has) had a successful delivery, and both you/she and your/her baby are now in good condition