Is it okay to decline a job after accepting a contingent offer?

Okay, so this is killing me! I recently moved to a new area, and I am 21 weeks pregnant with my second child. I have 9 months of experience, and have been kind of choosy in my job search so as to accommodate my family. I had an interview on Monday for a PRN- float pool position for a long term acute care facility, sometimes being pulled to urgent care centers scattered around the area. My schedule is determined by me, with the exception of one major holiday and one minor holiday and one weekend a month. With that being said, the days that I choose are not guaranteed and I won't know if I have to go in until the morning of. Also, I will pretty much be working 12 hour shifts starting anywhere from 7a-2p and going until 7p-2a. Good pay, minimum requirement of 48 hr/month, no benefits but I don't need them anyway, good experience. They called on Tuesday and made a contingent offer based upon my background check and references, and I accepted.

Tuesday night, I get a call from job A's sister hospital with an interview for a job in employee health. I have an interview tomorrow (Thursday) with the nurse manager. Now, this would be the perfect job for a number of reasons. Pay would be less, but I would be getting 40 hrs/week. M-F, 9-5, no weekends or holidays, consistent scheduling. The environment is less stressful than an acute care setting, no 12-13 hr shifts on my feet (only an issue as my pregnancy progresses,) and most importantly in my opinion, I get to be home for karate/violin lessons and I get to have dinner with my family nightly. With my husband in the military, there's a great chance that I will be acting in the capacity of a single parent when it's time for my husband to travel for work at the last minute. It will be much easier for me to send my son to after school care until 5:30 pm than it would be for me to find a reliable babysitter until 2-3am while working job A.

I would hate to burn a bridge, and I don't want to be unprofessional. I don't want to make the wrong decision here, but job B seems so much better for me and my family right now. Are these acceptable reasons to decline a job after accepting verbally? What do you guys think?
I forgot to mention that I would not be officially declining job A until job B has made an offer.
I think you have to do what's best for yourself.
Does it matter whether we think it's "ok"?You need to do what is right for you and your family. It matters not what we think.
I would do what's right for myself and my family. But since it's a contingent offer, it's not even in writing yet...so even more in your favor. Congrats on the new baby!
Sure, you can decline a job after accepting a contingent offer. However, I would not decline anything with job A until you hold an official job offer from B (in writing from HR) firmly in hand. Many a verbal or contingent offer has suddenly evaporated before an applicant's eyes for various reasons, and you don't want to find yourself without any job offers.Best of luck whatever you decide and with your pregnancy.
Whichever decision is best for you then go for it! I have had 2 new hires that accepted the position I offered but then the day of orientstion they called and said they found a better offer. It is perfectly okay to do that as long as it is right for you and your family!!!
Quote from KellyRN2013Whichever decision is best for you then go for it! I have had 2 new hires that accepted the position I offered but then the day of orientstion they called and said they found a better offer. It is perfectly okay to do that as long as it is right for you and your family!!!
Quote from MissMoo25Were they looked poorly upon for doing so? For reference purposes