I was undiagnosed with BiPolar II symptoms when I had my daughter in 2009. At the time of my pregnancy, I had just started taking Lexapro for anxiety and immediately ditched it when I learned that I was pregnant. My pregnancy was amazing- I managed to stay in a calm state that bordered on hypomania (but I was able to sleep with no problem) throughout the pregnancy. I was very strict with my diet and exercise during the pregnancy. Looking back, pregnancy was without a doubt one of the best things to ever happen to me. (Yes I threw up constantly until I was 12 weeks pregnant so it wasn't the easiest experience).
After having my daughter, a lot of things lucked out for me. I had a lot of help from friends, my husband at the time was very supportive in helping me get up at night for feedings and changing the baby's diaper prior to feedings, and my mother-in-law was very supportive.
As my daughter got older (around six months), my husband became very indifferent to our daughter. He started commenting that she was "boring" and complained that she couldn't do anything. More of the parenting responsibilities fell on me.
When my daughter was 3 and a half and was starting potty training- the stress of it (did not cause) but contributed to my inpatient hospitalization for six weeks. I was very fortunate to have a strong level of family support during that time. I was also protected under FMLA for my job and qualified for short-term disability insurance payments through my employer.
Fast forward five years- my daughter is the light of my life. I couldn't possibly imagine my life without her. She keeps me motivated, and has taught me so much about myself. I am very lucky that she has an easy-going nature and doesn't have any special needs.
Things with her Dad did not work out, and he now lives in another state and I have full custody. I didn't imagine that outcome for my daughter when she was born.
If I had a bipolar diagnosis at the time of my pregnancy, I am not sure if I would have chosen to have a child. One of my fears was that I would inherit my mother's schizophrenia, and I originally planned to have kids when I was older and past the point of getting a diagnosis.

A few things to consider:
1). What type of parenting approach do you and your parent have? How involved does your partner want to be? How is he around kids? What values does he want to pass down? How well does that pass down?
2). What is your support system? What role will they play with post-partum depression? How much can they realistically help you with your child?
3). What is your plan if you get hospitalized? How are savings? Do you have a job with short-term disability coverage, or can you purchase a policy? Are you covered under FMLA?
4). Do you plan on working? Can you get by on one income? If you work- what are your daycare or family options? Having a great daycare is an excellent peace of mind, but it's also very expensive for an infant.
5). Do you have a good ob-gyn for high-risk pregnancy? If not, you may want to shop around.

In short, no one is ever truly ready to be a parent.

But you can be bipolar, survive set-backs and still love being a parent. My friends tell me that I'm great mom. I do my best at it.