Can anyone please help me with the principal diagnosis for my inpatient OB case? I am not familiar with coding OB charts.

A 34 wk preggie came in due to N&V and contractions, intact membranes, and admitted d/t N&V and to r/o decreased fetal movement and preterm labor. She was given betamethasone and on fetal monitoring. She was discharged and was advised on what to watch out for for preterm labor. Discharge summary noted that work up for preterm labor was negative.

What diagnosis should I use? Can I use a Z code for it? Or is there an O code I could use?

Thank you for your input. Have a good one!