You do not need to use the weeks of gestation codes.
per the ICD-10 guidelines:
Codes from chapter 15 and sequencing priority Obstetric cases require codes from chapter 15, codes in the range O00- O9A, Pregnancy, Childbirth, and the Puerperium. Chapter 15 codes have sequencing priority over codes from other chapters. Additional codes from other chapters may be used in conjunction with chapter 15 codes to further specify conditions. Should the provider document that the pregnancy is incidental to the encounter, then code Z33.1, Pregnant 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.
AND, the notation below the Z3A codes, states:
Code first obstetric condition or encounter for delivery (O09-O60, O80-O82)
it is not required with the Z33.1.