Best time for Fertility Massage?

[HelenP]

Does anyone know when it's most effective to give a fertility massage? Before 'try for baby', between 'try for baby' and taking pregnancy test or during one of the trimesters? 

Thanks

[oshizu]

@HelenP

Formerly in my immortal dynasty household of 6 sims, I moved in an elder to prevent multiple births, then had the female sim get pregnant.
That elder died before the pregnant sim's due date, however, and she gave birth to twins.

For this reason, I think that giving a fertility massage very late in the pregnancy makes more sense.
But even with fertility massages and both parents having the fertility trait, I don't consistently get multiple births. 
 

[Playalot]

I may be wrong in this but my understanding is that the best way to get twins is simply to have the sims try again for a baby after you see the target sim look nauseous and have the diaper or building blocks thought bubbles. I use this 'trick' and it never fails. It seems as if the game allows for multiple babies when Try for Baby is used after the sim is actually pregnant but before there is a moodlet. Obviously for this to work you can not take a pregnancy test as once the sim knows they are pregnant then the number of babies is locked in. Much like if you have a doctor sim predict the gender, from that point on the gender is locked in.

I have never used any fertility massages or the reward trait or even the Ley Line lot trait but by using this 'trick' I can basically choose when my sim has twins.