Many of my patients know that I am a huge proponent of perineal massage.
I was first introduced to it via my midwife in Japan with my first son. I won't go through the fine details of what the perineum is or any of the science behind it. I have linked a few good articles that already do that.
I'll just get down to the nitty-gritty here:
First off, don't do this until you are 37 weeks pregnant. This is the advice I received from my midwife and it is the advice I give to my clients. I would hate for you to disrupt a perfectly healthy pregnancy on accident before it was baby time.
To begin, wash your hands or have your partner wash theirs. This massage is perfectly fine to do as foreplay if you feel comfortable but make sure that your hands and fingernails are clean.
I like doing this in the bath so that my internal tissues are soft and supple. Feel free to do this outside of the bath but only use oils or lube that are healthy to use down there. After everything is lubed and/or softened uptake the index and middle finger of each hand and gently insert them into the vagina. Insert up to the last knuckle or as far as your hands/body will allow.
Now gently start to stretch out the inner tissues of the vagina and the outer tissues of the perineum. Stretch in all four cardinal directions: north, west, south, and east. Next, stretch north-east, north-west, etc.
That's it! Do this once a day until your delivery.
For more articles about this please check out the following link:
Note: This article says to use the thumbs but I feel the index and middle finger are more adept.