The Lancet is a technical magazine. This needs readers to know. For example, how to make tonsils is better. This topic is suitable for The Lancet, and there is basically no need to know why. Lo's work is excellent, not because he first found the genetic information of a fetus (not a child) from the body of a pregnant woman (not a mother), but because he got these genetic information through blood and multiplied it by PCR, so that he could copy it and then study it. The article has repeatedly stressed that there is no need for puncture after blood collection. Of course, at that time, the method was not so clever. Only 70% to 80% of 43 pregnant women are pregnant with boys, depending on whether plasma or serum is used. The above is why the traditional method of Tang sieve in the middle stage is puncture, but now it only needs the blood of pregnant women. In the above picture, the highlighted part is the sample collection method in the Lo article, which specifically shows the data of ten pregnant women as the control group. Please note that there is no indication whether these ten women have a history of pregnancy. Look, what's their conclusion? It is a technical question which scale they compare is better. Then I pointed out that the method I reported was reliable, and I deliberately used irony to guide pregnant women's plasma as a neglected source of DNA collection. From beginning to end, the article did not talk about the so-called distant ancestors. Because the research object is only pregnant women, no one knows what the state is after pregnancy. It should be emphasized that the ten non-pregnant women here as a control did not know whether they had a history of pregnancy, but none of them detected the target genetic material. This is the significance of the control group.