Trying to determine the absorption of a vitamin, any vitamin, by putting it in a glass of water and waiting for dissolution won't tell you anything other than how long it takes to dissolve in water. The acids in your stomach are designed to do some of the digestive work, but there's also a swishing action of the stomach and enzymatic activity. Even the so-called vinegar test doesn't tell much. Our stomach acid is much stronger than vinegar. Depending on the nutrient, some things are suppose to be able to survive through the stomach acid so it can be absorbed in the small intestine. Centrum and the like that dissolve in water will likely not be bioavailable for nutrient absorption.

When you ask about a "good" vitamin for pregnancy that depends on your definition of "good". A high quality multivitamin for pregnancy is one that you would take in low doses divided over three times a day, just like you would eat 3 good meals a day. Most people (and I'm not incinuating you are one of them) are really referring to a minimally adequate multi when they say "good". What is your definition of "good"? (p.s. I'm not a rep for any supplement company, not selling anything, etc., so I have no underlying reason for saying this) Marie