Lu Yuqing actually knew the pregnant woman. She was Lu Yuqing's assistant.
Zhao Zhuangzong was the father of the child! They had probably been in an affair for about two or three years by now.
After Zhao Zhuangzong had a child out of wedlock, he didn't divorce Lu Yuqing to marry the child's mother. Instead, he lied to Lu Yuqing and convinced her to adopt a child to stop his mother's nagging and whining.
Lu Yuqing was moved by Zhao Zhuangzong's consideration. They adopted a baby boy. Sure enough, Zhao Zhuangzong's mother stopped nagging at them anymore. Lu Yuqing felt weird about her in-law's peculiar behavior, but at the same time, she could be rest assured that her mother-in-law would stop her nagging.
Speaking of which, it wasn't that Lu Yuqing didn't want children, but they couldn't seem to have a child after they got married.