It is the providers responsibility to state that the

state, incidental, should be used in place of any chapter 15 codes. It is the
provider’s responsibility to state that the condition being treated is not
affecting the pregnancy.
2) Chapter 15 codes used only on the maternal record
Chapter 15 codes are to be used only on the maternal record, never on
the record of the newborn.
3) Final character for trimester
The majority of codes in Chapter 15 have a final character indicating the
trimester of pregnancy. The timeframes for the trimesters are indicated at
the beginning of the chapter. If trimester is not a component of a code, it
is because the condition always occurs in a specific trimester, or the
concept of trimester of pregnancy is not applicable. Certain codes have
characters for only certain trimesters because the condition does not
occur in all trimesters, but it may occur in more than just one. Assignment
of the final character for trimester should be based on the provider’s
documentation of the trimester (or number of weeks) for the current
admission/encounter. This applies to the assignment of trimester for
pre-existing conditions as well as those that develop during or are due to
the pregnancy. The provider’s documentation of the number of weeks
may be used to assign the appropriate code identifying the trimester.
Whenever delivery occurs during the current admission, and there is an
“in childbirth” option for the obstetric complication being coded, the “in
childbirth” code should be assigned.
4) Selection of trimester for inpatient admissions that encompass
more than one trimester
In instances when a patient is admitted to a hospital for complications of
pregnancy during one trimester and remains in the hospital into a
subsequent trimester, the trimester character for the antepartum
complication code should be assigned on the basis of the trimester when
the complication developed, not the trimester of the discharge. If the
condition developed prior to the current admission/encounter or
represents a pre-existing condition, the trimester character for the
trimester at the time of the admission/encounter should be assigned.
5) Unspecified trimester
Each category that includes codes for trimester has a code for
“unspecified trimester.” The “unspecified trimester” code should rarely be
used, such as when the documentation in the record is insufficient to
determine the trimester and it is not possible to obtain clarification.
6) 7th character for fetus identification
Where applicable, a 7th character is to be assigned for certain categories
(O31, O32, O33.3 - O33.6, O35, O36, O40, O41, O60.1, O60.2, O64, and
O69) to identify the fetus for which the complication code applies.
Assign 7th character “0”:
• For single gestations
• When the documentation in the record is insufficient to determine the
fetus affected and it is not possible to obtain clarification.