If you are just now signing up for a new health insurance plan you should sign up to get healthy insurance maternity coverage before you get pregnant. If wait until you are pregnant to get maternity coverage, it may be considered a pre-existing condition. This means that this pregnancy will not be covered.
You may be able to get maternity coverage if you are already pregnant on a group plan that does not have any maternity restrictions on it. However, you will not be covered under an individual health insurance plan or even under an individual family plan if you are pregnant at the time you apply.
If you are of the age that you may need maternity coverage at some point in the future, you are much better off adding the coverage to your plan from the beginning. When you do become pregnant there will be no question about your coverage. Some individual and family plans have a waiting period which you should find out about also. Some plans will require that you have the maternity benefit on the plan for 12 months before it is active.
Be sure to read the guidelines of the plan you are applying for before making a purchase. If this is something that you will likely need in the next few years, be sure you understand completely what will be available to you. You don't want to leave this issue to chance.
You will pay a higher premium for health insurance maternity benefits but it will be worth it. If you have a normal pregnancy, your medical care costs may be between $2000 and $3000. However, if you have complications with your pregnancy your medical costs can reach as high as $100,000 or even more depending on the circumstances. Better to be safe and add health insurance maternity benefits than to go without it.