This presupposes that frequent ultrasounds offer benefits and have no risks. One interesting study was done on women with suspected IUGR (intra-uterine growth retardation/restriction -- small babies), and they randomly assigned women to regular ultrasounds (like you're wanting) or not, and the women who got regular u/s ended up with smaller babies than the women who got no extra/special u/s. Thus it appears that u/s can affect babies, and sometimes cause the problems they're supposed to prevent.
Doppler is a form of u/s, and when I was pregnant with my first, my midwife used Doppler to hear his heartbeat, and he always moved away from it, until he got too big to "run and hide", and then he would just try to kick it away. You can't convince me that it was a fluke every single time (even in labor!). So, despite the fact that we can't hear u/s, that doesn't mean it doesn't affect us. In fact, one doctor discovered that u/s makes fluid move, and a recording of it sounded like a subway train.
No, I'll pass on the u/s unless it is necessary; I don't want my babies exposed to that.