This is a very popular maternity portrait, one you will see in the portfolio of nearly every maternity photographer (including myself).
One of the reasons this pose is so popular is that it is sweet, easy to accomplish, and very low pressure for the mom-to-be.
However, there are some downsides to the pose. Because it is used so often, it lacks originality. Because it is nearly always done as a belly-only photo, it risks being anonymous. Finally, if it is not done artfully, the result is a poor, graceless photo at the lowest common denominator. You need to be careful of some potentially awful choices that can make this a terrible photo.
The first thing you want to do is to get the hands into the right position. If the negative space between the two hands does not look like a heart, then don't take the photo. Unfortunately, if the thumbs are not clearly down, the hands cease to look like a heart and instead make the American Sign Language sign for "vagina." Hopefully not what you are going for.
You want to make sure you get a good, soft light on the belly. Window light, especially on a cloudy day, will work very well.
Avoid on camera flash at all costs. Keep your light slightly off to one side, but not so far that you have deep shadows on the hands. It helps to have the mom-to-be manicured, as cracked fingers or ragged nails are distractions.
The hands should rest comfortably against the belly, creating the heart shape in what appears to be a casual manner.
Some things you should consider:
First, a lot of photographers will have the dad make the heart with his hands on the mom's belly. While the idea is cute in theory, it is awful in practice. Why?
Because she looks like she has man hands!
Second, you may find the mom's hands are much darker than the skin on her belly. This type of a mismatch can look awkward. Soft lighting will help, as will processing color into black and white, favoring the blend which evens out the tones.
Finally, I implore you to not to use "selective color." Selective color tends to be poorly used in maternity photos, but in this case it is just awful because the "selective" area of red or pink heart-shaped skin ends up looking like a wound or a rash on a pale cadaver. Though it pains me to have created it, I show it to you below:
