Hello.
What we know today is that Bipolar Disorder definitely runs in families. But there are different estimates for the exact percentage when it comes to a specific scenario such as your family. And none are exact. What we also know is that the risk to children is around 20% when one parent is affected. But neither you nor your husband have the Bipolar Disorder. So, the risk to your kids is definitely much less than 20 percent. There is no conclusive answer to how much the risk reduces if none of the parents have BD.
Your husband's chances of getting BD were 1:5 (one in 5), assuming only his mother had BD. What it means is he could have been the one with BD out of "five children" to his mother. And the risk stays the same for all his brothers and sisters. And even if the risk is 20%, it was still a risk. But he does not have BD. And since he does not have BD, the risk to your child would be much less than what your husband had. It is difficult to mention what percent exactly.
There is another concern however. You may need to find out the pattern of expression of BD in his family for the lat few generations. BD may skip generations. And if so, the maximum risk to your child would be somewhere in between 1% (same as for general population) and about 10%, a rough estimate often considered valid for children whose grandparents have the disorder. A 10% risk would mean one in ten children might have Bipolar Disorder.
There is slightly increased risk of Bipolar Disorder in children when the ages of both the parents are above 30yrs at conception. Statistically speaking, you and you husband are 1.45 times more likely (than "parents with no family history" ) to give birth to a child who might develop Bipolar Disorder. You need to see this in context of the other things we discussed above. This figure of 1.45 does not tell about an increased risk of BD in your child, but it tells about your chances of giving birth to a child with possible BD. And if that is to be translated into what is real, the additional increased risk due to age factor appears insignificant. It might have been significant if one of you had BD.
Lastly, environmental factors also play a major role in shaping up the personality and experience of a child. It's the age old 'Nature Vs Nurture' question. Nurture might be able to prevent BD from manifesting in a person and the person may go on with his life without any difficulties. You may keep this aspect in sight when thinking about your child.
I hope this helps a bit. Take care and I wish you good luck in your efforts.
Abhijeet Deshmukh, MD
References sources: PubMed (Menezes et al, 2010), NIMH, Statistics (for Hazard Ratios)
(This post is for the purpose of providing medical information and is not a substitute for a face-to-face consultation with a doctor. This post is not intended to give or rule out a diagnosis, create a doctor-patient relationship or replace an existing one. I am not able to diagnose medical conditions online. Please consult with your doctor or a qualified healthcare provider for diagnosis and treatment options)