Is a pelvic ultrasound as good as a transvaginal u/s at measuring size of ovaries? Are they both accurate?

Possibly equal. It really all depends on how well the ovaries are seen. If the bladder is full and the ovaries are well demonstrated transabdominally then measurements will be as accurate. Transvaginal ultrasound usually provides a more detailed look at the ovaries because the transducer is right next to them. However, sometimes the ovaries are hard to find transvaginally. Each patient is different.