Topics here dealt with are clinically important. The strength is a large study number. I have some concerns.

General 1. Please strengthen your results more straightforwardly. I understand you have described it here and there. However, to readers, your strength is unclear. You described previous data from page 11 to 12; however, it is not coordinated. You should clearly describe, "what differs and what agrees with the present data; if disagrees, why the previous data disagreed?; it should be clearly and definitely described. If you believe that yours reflects the "fact", criticize the previous data that is controversial to the present data. It may be good to more emphasize the large number and good registration system in the present study. Emphasize the merit of your study and then criticize the study which yielded contradictory data. This is the very point that makes this manuscript stand. 2. Please consider the paragraph. The present paragraph making is not good. Please describe the "topic sentence" in the very beginning of each paragraph, followed by "content sentence". I mean that you had better put the "main message" of the corresponding paragraphs just in the beginning, followed by its explanation. Readers cannot follow the one without this structure. Readers are all crazy busy and thus give them the message in the first sentence in every paragraph. 3. In the conclusion of Abstract, you confined the topic to DD twin. This is peculiar. The difference between DD and all twins is only one: the rate of NICU admission at 37 weeks. You did not otherwise analyze the difference between DD and all twins all throughout the manuscript. Conclusion should be "In uncomplicated twin pregnancy elective cesarean section can be best performed between 37+0 and 39+6 weeks of gestation". This is sufficient. Putting DD in this section leads to misunderstanding of the readers. Rather, put "uncomplicated" in Objective of Abstract. 4. You used cesarean section more than 10 times. Use Abb., "CS". It saves space. 5. Discussion: Limitation paragraph should be put in the 2nd last paragraph or at least in the latter half. You need not "confess your weakness" in this "sales" paragraph, i.e., in the 2nd paragraph. Furthermore, please look at the volume of Discussion. Approximately a half consists of "limitation= weakness". To be honest and cautious is good as a scientist; however, readers will feel that "this manuscript is full of limitation". Strengthen your point instead of detailed explanation of "weakness". The second paragraph should consist of "to strengthen your data".
6. Paragraph consisting of "one sentence" cannot stand as far as the medical writing is concerned although it can stand in the "Novel" or Poem". Please look at page 4, last line. 7. Epoch making paper regarding this topic may be better cited. Minakami H, Sato I. Reestimating date of delivery in multifetal pregnancies. JAMA. 1996 May 8;275(18):1432-4. Erratum in: JAMA 1996 Aug 14;276(6):452.

Specific Comments 1. page 4, line 3 from the bottom; delete "relatively". (relatively? Compared with what?) 2. page 6, Outcome measure, divide them into several paragraphs. 3. page 7, line 13, what is (1987). Delete? 4. page 8, line 17, insert comma after "1b". 5. page 10, line 11, delete "relatively". We usually do not use "relatively". To compare with what?? 6. "small for date (gestational age)" and "large for date" should be "light for date" and "heavy for date", respectively all throughout the text. "Small for date" indicates small both in weight AND height. WHO criteria. 7. page 12, line 15, "intrauterine"; one word and not two words. 8. Table 1a; line 3; "section caesarea" is wrong expression. "Number of mothers (%)" may be better. 9. Table 1b; line 3; "number of neonates (%)" should be used. 10. Table 4; line 2; "number of neonates" should be used.

If you have a chance to revise the manuscript, I strongly advise you that you had better make the manuscript structure better. I partly advised you in this Comment how should you do it. However, as you may know, "point-by-point suggestion" and then "incorporating them into revision" is by no means sufficient to make the structure correct. Your data is good; however, the structure of the manuscript is not good. Please revise the one extensively not only according to my suggestion but also making them completely anew by your own judgment.