The concentration of oxygen falls during a flight and women in the late stages of pregnancy can be affected by oxygen deficiency.
For that reason, Peach does not recommend that passengers fly within 14 days of their expected delivery date, counted including the expected delivery date.

However, if the flight is essential, it is possible for pregnant passengers to fly under the following conditions. Passengers within 14 days of their expected delivery date (including delivery date).
 ・A doctor's certificate (written in English or Japanese) must be submitted.
 ・The passenger must be accompanied by a doctor.
 Between 15 and 28 days before the expected delivery date (including delivery date).
 ・A doctor's certificate (written in English or Japanese) must be submitted.

For more information about pregnant passengers, please see here.