Ob-Gyn Coding Alert

Beware of reporting AMA without trimester specificity.

A subscriber recently asked, “If a patient presents for a viability ultrasound and is also advanced maternal age (AMA) or otherwise high risk, should you code Z36.87 (Encounter for antenatal screening for uncertain dates) first, or should the high-risk pregnancy code, such as O09.521 (Supervision of elderly multigravida, first trimester), be primary?”

This is a common obstetric coding question because early pregnancy ultrasounds often involve overlapping clinical reasons for the encounter. Your sequencing decision should reflect the physician’s documented reason for the visit and the circumstances chiefly responsible for the service performed.

Start With the Purpose of the Encounter

Before assigning diagnosis priority, you should determine why the patient was seen and the clinical intent of the ultrasound.

Ask yourself why the provider performed the ultrasound:

• Was the ultrasound primarily performed to establish gestational dating or evaluate uncertain pregnancy dating? or
• Was the ultrasound primarily focused on management of a high-risk pregnancy?

Important: Your sequencing should follow the provider’s documented reason for the encounter.

Understand When You May Sequence Z36.87 First

You may sequence Z36.87 (Encounter for antenatal screening for uncertain dates) as the primary diagnosis when the documentation supports that the primary purpose of the encounter is evaluation of gestational dating or confirmation of gestational age due to uncertain pregnancy dating.

For example, if the documentation states, “Patient presents for viability and dating ultrasound. LMP [last menstrual period] uncertain,” you may sequence Z36.87 as the primary diagnosis because the chief reason for the ultrasound is to establish gestational dating and viability. If the provider also documents AMA, you may report O09.521 as an additional diagnosis when it is documented and clinically relevant to the patient’s pregnancy management.

Know When the High-Risk Pregnancy Code Should Be Primary

You can sequence one of the O09.- (Supervision of high risk pregnancy) codes as the primary diagnosis when the documentation supports that the encounter is primarily focused on supervision or management of a high-risk pregnancy.

For example, you may report O09.521 or O09.511 (Supervision of elderly primigravida, first trimester) when the physician documents the AMA and the visit is directed toward high-risk pregnancy management. To illustrate this, the documentation could state, “AMA pregnancy referred for first trimester viability evaluation due to elevated maternal risk.” You would sequence O09.521 or O09.511 as the primary diagnosis, depending on whether the patient has had more than one pregnancy or if this is their first pregnancy, respectively, because the encounter is focused on management of a high-risk pregnancy. You may also report an additional appropriate diagnosis code to reflect other clinical indications for the ultrasound when documented.

Remember: O Codes Generally Take Priority in Pregnancy

The ICD-10-CM Official Guidelines state that Chapter 15 pregnancy codes O00.- (Ectopic pregnancy) through O9A.- (Maternal malignant neoplasms, traumatic injuries and abuse classifiable elsewhere but complicating pregnancy, childbirth and the puerperium) have sequencing priority over codes from other chapters in most maternal records when a pregnancy complication or condition is present and managed during the encounter.

That means if the documentation clearly supports supervision or management of a high-risk pregnancy, the O09.- code will often be the more defensible primary diagnosis.

Don’t Automatically Assume AMA Is the Primary Reason

One common coding mistake is automatically sequencing AMA first simply because the patient is over age 35. AMA status alone does not necessarily determine the chief reason for the ultrasound.

You should instead base sequencing on:

• The documented indication for the study,
• Physician assessment, and
• The condition chiefly responsible for the encounter.

Use These Documentation Clues in Your Code Decision

You can sequence Z36.87 as the primary diagnosis when the documentation indicates that the purpose of the visit is related to uncertain dating or confirmation of gestational age. This includes situations where the provider documents terms such as “uncertain LMP,” “dating ultrasound,” “confirm gestational age,” “viability scan,” or “size/date discrepancy.”

The O09.- codes may support primary sequencing when the documentation indicates that the visit is primarily focused on management of a high-risk pregnancy. This includes situations where the provider documents phrases such as “high-risk pregnancy management,” “AMA supervision,” “maternal age-related risk,” or “referred for high-risk OB evaluation.”

Here’s a chart that may be helpful for choosing your diagnosis code:

Recognize Common Pitfalls That Can Lead to Denials

One common pitfall is sequencing a screening code when the pregnancy is actively managed as high risk. If the documentation clearly supports supervision of a high-risk pregnancy, reporting only Z36.87 may not accurately reflect the primary reason for the encounter or support medical necessity.

Another frequent issue is reporting AMA without trimester specificity. The O09.- codes require trimester-specific assignment, so you must ensure you select the correct code based on gestational age, such as O09.521 for the first trimester, O09.522 (Supervision of elderly multigravida, second trimester) for the second trimester, or O09.523 (Supervision of elderly multigravida, third trimester) for the third trimester.

Important: Coders should also avoid assigning “elderly multigravida” or AMA supervision codes without provider documentation. You should not code AMA-related supervision based solely on maternal age; the provider must clearly document the condition or indicate that the pregnancy is being managed as high risk due to maternal age.

Learn a Practical Coding Approach You Can Use

When you code viability ultrasounds in high-risk pregnancies, you should first identify the documented reason for the ultrasound. You should then determine whether the encounter is primarily for dating and viability or for high-risk pregnancy management.

Next, you should sequence the diagnosis that best reflects the chief reason for the encounter. You should also add secondary diagnoses that affect the patient’s care and clinical management.

Finally, you should verify trimester specificity for all O09.- codes to ensure accurate reporting.

In many cases, you can report more than one diagnosis; however, the sequencing should always follow the provider’s documented focus of care and applicable ICD-10-CM pregnancy coding guidelines.

Suzanne Burmeister, BA, MPhil, Medical Writer and Editor