If I was prescribed a medication for extreme morning sickness during my pregnancy and then my son was born with developmental delays, can I sue for malpractice?

It *may* be grounds for a suit. The two key issues are:

1) Is there a causal link--that is, did the medicine cause the developmental delays. The fact that two things occured together do not prove that one caused the other: to use an admittedly obvious example, it's very likely that you watched TV and listened to music during your pregnancy, and also probably ate or drank something with caffeine at some point (soda, tea, iced tea, coffee, chocolate, etc.), but that doesn't mean that the TV, music, or caffeine caused your son's problems.

For a lawsuit, you'll ultimately need an expert medical opinion, such as from some doctor, that links the medicine to the developmental delays. If you don't have that at present (i.e. don't have some determination or opinion from one or more of your or your son's doctors that the medicine caused the problem), then to at least seriously consider a lawsuit, you should, at a minimum, look for well-regarded medical literature or studies (such as in medical journals or at least respected national media) which show that this type of medicine can cause this type of issue. If you can't find any support to show that the medicine caused the developmental delays, then you likely do not have a viable lawsuit. If you can't show a causal link, there is no legal claim.

2) Even if the medicine could in some cases cause these problems, then the next issue is whether it was careless or unreasonable to prescribe it for you. If the likelihood or probability of the harm was very remote, and meanwhile you were suffering greatly from the extreme morning sickness, then it may have been reasonable to prescribe. For example, say the chance of the medicine causing the delays is 1 in a million; with such strong odds against a problem, with you suffering greatly, giving you the medicine may have been a reasonable medical decision. (Doctors do not need to be perfect; they just need to make well-informed, reasonable decisions.) So not only do you need to know if the medicine could have caused the problems, but you need to have some sense or idea for how likely that are--at least at the dosage you were taking--since that will help determine whether the doctors made the right call or not.

You should speak with an experienced medical malpractice attorney--many provide a free initial consultation, and you can ask about this before making the appointment. The lawyer can help you understand what you'd need for a case, evaluate the strength of you case and what it might be worth economically, and also advise as to what it might cost you to bring a case, since all those factors must be considered.