It's still important to eat nutritious foods, but prenatal vitamins can help ensure you're getting enough of these essential nutrients during pregnancy:

During pregnancy, the active form of vitamin D increases significantly, particularly in the second and third trimesters. During this time, the baby's bones are developing, as are the brain, the nervous system, and the other organs.

Recently, there has been a great deal of research about vitamin D and maternal, fetal, and infant health. Although much more research is required, it appears that vitamin D contributes to improving pregnancy outcomes, such as decreasing the risk of pre-eclampsia, and improving length of gestation, birth weight, and infant bone mineralization. It also appears that sufficient vitamin D in early life may decrease the risk of health problems later in life such as schizophrenia, brain tumours, asthma, multiple sclerosis, and autoimmune diseases such as type 1 diabetes.

These findings don't mean you should run to the local pharmacy for a mega dose of vitamin D. In fact, there are potential adverse effects of too much vitamin D on the cardiovascular system and allergies. Much is still to be learned and hopefully gained from further research. So, if you are pregnant take a pregnancy vitamin and look for one with at least 200 international units (IU) of vitamin D.

Keep in mind that standard prenatal vitamins don't include omega-3 fatty acids, which help promote a baby's brain development. If you're unable to eat fish or other foods high in omega-3 fatty acids or choose not to, your health care provider may recommend omega-3 fatty acid supplements in addition to prenatal vitamins.

It's best to start taking prenatal vitamins three months before conception. This is because the baby's neural tube — which becomes the brain and spinal cord — develops during the first month of pregnancy, perhaps before you even know that you're pregnant. Taking prenatal vitamins before conception is the best way to help prevent neural tube defects.