Personally, I feel that if you have a legitimate concern regarding your health that is affecting your everyday life, such as sincere pregancy worries, that is a time when going to the doctor can be racked up to I AM SICK. That's why work gives us sick days, because if something is hurting you, you are "sick". You don't even have to tell them why; it is none of their business. People call in sick all the time for much less sincere reasons.
I am a hard worker who prefers to use comp or vacation time over sick leave, but if my work situation was such that I did not feel comfortable making an appointment at the doctor ahead of time and pressures were exerted from above that we were understaffed, I would not hesitate to take the morning off under the guise of "sick", whether you have to say stomach flu or medical concerns. Because it is a medical concern, and something is wrong with your stomach! People take sick time when their children are sick, and you are concerned that there is something wrong with your child.
In the great scheme of things, 4 hours of work is nothing compared to your continued health and the health of your baby. Seriously, if you did have a concern and did not get to the doctor and (heaven forbid) had pregnancy complications, how much work time would you lose healing and grieving?Take care of yourself, take care of your baby, and let someone else heft the kids for a while, eh?
(Getting off the soapbox....)
Take care of yourself, mama. Now is a time to be selfish and to follow your intuition, no matter what anyone else says.