You may find it very worthwhile to do a rebirth, which is like a new game+ where you get to keep your level and all items that you have in the bank. To do a rebirth Lona must give birth to a human, moot or deepone baby. If you did it right you get the option to be reborn as whatever baby you had when Lona dies. Once reborn everything except the above mentioned will be reset as if you started a new game, including your loan status with the backstreet merchant if you happen to have one which, if you're gonna rebirth anyway, why wouldn't you?
To save yourself some time and eliminate all the guesswork I recommend getting a combined total of 10 stacks of either "Horny (drugged)" or "Womb Seedbed" as each of these will increase preg_rate by .1 for a guaranteed pregnancy at 10 stacks. You can get 10 stacks of "Horny (drugged)" from drinking 5 "Joy Water" which you can buy using a loan or selling your ID (you're going to get a new one anyway), but they can be stolen from from FishtopiaR as well. If you're somehow in possession of "Witch Juice" drinking 1 of those will work as well, just make sure to strip all equipment before drinking it or Lona will do it after and you won't be able to pick them up again.
There is no feedback until later stages of pregnancy, so you must either sleep until that happens or simply assume pregnancy after sleeping once with any amount of semen in the womb if you have 10 stacks.
If you want to be certain of things go to Elise, he can tell whether Lona is pregnant and you can find out what kind of baby it is by aborting it. This will kill the baby but you can reload your save just before you do it.