When a female HUD user mates with a male HUD user the result can be conception and pregnancy. However, sometimes the female HUD user wishes to be pregnant without the mating beforehand. So, if you want to use the female Mama Allpa HUD for a pregnancy without having any male HUD involved, you can set yourself to pregnant manually. 

These are the steps how to get there:

1. The menu for a manual pregnancy can only be reached within day 1 and day 2 of your monthly cycle. This means, if you are past day 2, you either need to wait until you are again there or you have to reset your cycle. For resetting your HUD and with that your cycle go to
   HUD - Assistant - My HUD - Reset.
   A warning appears in local chat. If you want to proceed, touch "Reset Yes".

2. Now, your HUD being at Cycle day 1, go to Assistant - My body - Condition - Yes Manual

3. Select how many weeks you wish to be at. A human pregnancy lasts 40 weeks, measured from the first day of the last menstruation. 20 weeks would be half way through. Chose the value to your likes

4. Select how many babies you would like to have. 

The looks of your baby will be how you set your traits, as there is no other partner involved. You need to have set your traits before you set up your pregnancy.
The belly-grow mechanism is always assuming a human pregnancy with one baby. If you do not play a human character or you want to have really big bellies with multiple babies you need to look for third party options. Also, the result of the belly-grow, the look, will vary greatly from mesh-body to mesh-body.